ML20033B852
| ML20033B852 | |
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|---|---|
| Site: | 07001359 |
| Issue date: | 04/30/1981 |
| From: | Crosbie K, Maschka P IRT CORP. |
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| Shared Package | |
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| 19857, IRT-4141-012, IRT-4141-12, NUDOCS 8112020350 | |
| Download: ML20033B852 (95) | |
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IRT 4141-012 IRT CORPORATION RADIOLOGICAL SAFETY GUIDE Prepared by P. R. Maschka, Health Physicist K. L. Crosbie, Radiation Safety Officer iRT Corporation 1:~J'l Cl h y a
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I' QI' W'm,m,m.-.g j[d instrumentation Research echnolog February 1981 (Revised April 1981) 7650 Convoy Court. P O Box 80817 San Diego. Cakfomia 92138 714 / 565-7171 Telex: 69-5412
1 TABLE OF CONTENTS 1.
IN TRO D U C TIO N...........................
1 2.
PURPOSE..............................
3 3.
BASIC NUCLEAR PHENOMENA 5
3.1 A tom i c S tru ct ur e.........................
5 3.2 Radiation 7
3.3 Particulate Radiation.......................
7 3.4 Electromagnetic Radiation.....................
8 4.
INTERACTION OF RADIATION WITH M ATTER..............
9 4.1 fonization..................
9 4.2 Absorption or Capture....................... 10 4.3 Anni hil ation........................... 11 4.4 Scattering...........................
11 4.5 Fission 11 5.
THE NATURE OF R ADIATION..................... - 13 5.1 Alpha Partides.......................... 13 5.2 Beta Partides 13 5.3 Positrons...........................
14 5.4 N eu t rons............................. 14 5.4.1 Elastic Scattering.....................
15 5.4.2 Inelastic Scattering..................... 15 5.4.3 A bsorption......................... 15 5.5 Gamma Rays and X-Rays 16 5.5.1 Photoelectric Effect 17 5.5.2 The Compton Scattering................... 18 5.5.3 Pair Production....................... 18 5.5.4 Gamma-N Reaction..
18 5.6 Protons............................. 19 i-5.7 Summary of Radiation Interaction..
19 5.7.1 Alpha Partides............
19 5.7.2 Beta Partides 19 5.7.3 Positrons 19 iii
TABLE OF CONTENTS (Continued) 5.7.4 N eu t r on s.......................... 19 5.7.5 G am ma and X-R ay s..................... - 19 5.7.6 Protons.......................... 19 6.
UNITS OF RADIATION MEASUREMENT................
21 6.1 Introdu'ction to Radiation Measurement I,aits............
21 6.2 Definitions of Radiation Units...........,......
22 6.2.1 Roentgen (R)...
22 6.2.2 Roentgen Equivalent Physical (REP).............
22 6.2.3 Radiation Absorbed Dose (RAD)...............
22 6.2.4 Relative Biological Effectiveness (RBE). Quality Factor (QF)... 22 6.2.5 Roentgen Equivalent Man (REM)..............
22 6.3 Curie (Ci)...........................
22 6.4 Radioactive Decay.......................
23 6.5 Half Life...........................
23 7.
BIOLOGICAL EFFECTS OF RADIATION................
25 7.1 Interaction of Radiation with Biological Systems..........
25 7.1.1 Direct Method......................
25 7.1.2 Indirect Alethod......................
26 7.2 Major Types of Biological Effects.................. 27 7.2.1 G ene ti c Ef f ects......................
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7.2.2 Somatic Effects 28 7.2.3 Specific Organ Response to Radiation............
29 7.3 Biological Experience of Radiation Damage.............
30 7.4 Radiation Exposure Limits....................
31 7.5 Background P.adiation Exposure..................
32 7.6 Effects of Whole-Body Doses Received in a Short Time........
32 8.
PRINCIPLES OF RADIATION DETECTION AND MONITORING TECHNIQUES...........................
35 8.1 Ionization Detectors.......................
36 8.1.1 Ion Cham bers.......................
37 8.1.2 Proportional Counters...................
37 8.1.3 Geiger Counters 38 8.1.4 Summary........................
39 8.2 Scintillation Detectors......................
39 8.3 Secondary Particle Detectors...................
40 iv 9
4
TABLE OF CONTENTS (Continued) 8.4 Photographic Detection Method..................
41 8.5 Thermoluminescent Dosimeters..................
41 8.6 Personnel Monitoring Equipment
. 41 8.6.1 Film Badges
.....................41 8.6.2 Pocket Dosimeters
. 42 8.6.3 Chirpers..
42 8.7 Survey Instruments.......................
43 8.7.1 Geiger Counters.....................
43 8.7.2 Juno Survey Meter 44 8.7.3 Victoreen 440 RF Survey Meter.
45 8.7.4 Victoreen 592B.....
46 8.7.5 The Snoopy........................
47 8.7.6 Alpha Survey Meters
. 48 8.8 Monitoring Techniques......................
49 8.8.1 Detection Operations..
49 8.8.2 Monitoring Operations...................
50 9.
RADIATION PROTECTION......................
51 9.1 External Radiation Protection 51 9.1.1 Time 51 9.1.2 Distance..
51 9.1.3 S h ie l din g.........................
5 3 9.2 Internal Radiation Protection..
56 9.3 Safety and Handling Considerations..
58 10.
RU LES AND REGULATIONS.....................
61 10.1 Title 10 CFR 19 62 10.2 Title 10 CFR 20 62 10.2.1 Exposure Limits 62 10.2.2 Personnel Monitoring 63 10.2.3 Signs..........................
64 10.2.4 Receipt of Radioactive Material 65 10.2.5 Incidents........
65 10.3 License Requirements......................
66 10.3.1 The Radiation Safety Committee (RSC) 67 10.3.2 The Criticality Safety Committee (CSC)..
67 10.3.3 The Radiation Safety Officer (RSO).
67 10.3.4 The Health Physicist (HP) 67 v
TABLE OF CONTENTS (Continued) 11.
THE LINEAR ELECTRON ACCELERATOR...............
69 11.1 Fundamental Linac Radiological Safety Rules............
71 12.
C ALIFO RNIU M-252..........................
73 13.
RU LES FOR SAFETY........................
75 14.
RADIATION WORK AUTHORIZATION.................
77 14.1 Procedures for Initiating an RWA.................
77 15.
SHIPMENT OF RADIOACTIVE MATERIALS 81 15.1 Shipments between IRT's San Diego Facilities............
81 4
j 15.2 Shipments to Other Companies..................
81 15.3 Shipment by Air 84 15.4 Shipment of Special Nuclear Materials...............
84 16.
DEFINITIONS...........................
85 1
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LIST OF FIGURES Figure 3-1 The Atom 6
3-2 The electromagnetic spectrum...................
8 4-1 lonization areas.......................... 10 5-1 Interactions of electromagnetic radiation 17 6-1 Defining the Rcentgen in terms of charge, energy, and biological effect. 23 6-2 Radioactive decay scheme for uranium 238.............
24 7-1 Molecular breakdown caused by radiation and water ions.......
26 7-2 Production of abnormal cells by radiation
. 27
~
8-1 lonization~ variation with applied voltage..............
36 8-2 Typical quartz fiber dosimeter..................
42 8-3 The G eiger Counter.......................,. 4 3 8-4 Juno Survey Meter
.......................44 8-5 Victoreen 440 RF Survey Meter..................
45 8-6 Victoreen 592 B.........................
46 8-7 The Snoopy...........................
4 7 8-8 Alpha Survey Meters 48 9-1 Inverse Square Law.........
. 52 9-2 Half-value layers for different electromagnetic energies as related to thickness of iron and lead, aluminum, concrete and water........ 55 10-1 The radiation symbol 64 11-1 Linear accelerator (Linac) f acility.................
70 12-1 Production of Cf-252 from Pu-242.................
73 14-1 Radiation Work Authorization
. 78 15-1 Radioactive Material Removal Record...............
82 15-2 Radioactive Material Shipping Record...............
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- 1. INTRODUCTION
'Vhen a person mentions radioactivity or nuclear energy, most people think of mushroom clouds or science fiction monsters. True, nuclear energy can be used for destruction,'but it ab has many peaceful uses such as generating electric power and treating cancer. Even "The Bomb" could be used for peaceful purposes such as digging canals or releasing natural gas or oil from rock deep within the earth.
Today there are millions of people working with radioactive materials in gov-
-ernment and private industry. The safety record of the nuclear industry has been extremely good with very few injuries from radioactivity. This excellent safety record has not been achieved by chance, it is the result of carefully planned and strictly administered radiation safety programs.
We live in a radioactive world. Radiation is all about us and is a part of our natural environment. All around us, there is cosmic radiation coming from the sun and outer space; there are naturally occurring radioactive elements in the food we eat and the water we drink; our homes, offices, and f actories are constructed of materials that contain radioactive elements; travel by jet aircraft exposes us to higher levels of cosmic radiation; and, modern medical practices can expose us to high levels of radiation from diagnostic x-rays and radioisotopes.
The levels of natural radioactivity vary from one area of the world to another.
People living in Denver receive 2 to 4 times as much radiation from cosmic rays as do the people living in San Diego or Los Angeles, and people living in some parts of South Africa, India, and China receive 10 to 20 times as much radiation from thorium and urnium as do the people in Southern California. Yet, there coes not appear to oe any ill effects to those people who receive these higher r diation doses.
Life on our planet developed despite this constant exposure to radiation. In f act, in past ages,' the natural background radioactivity was much higher than it is today because the earth's radioactive materials have been steadily decaying. Today with the development and use of nuclear energy, extremely high levels of radiation are being produced. People working in the nuclear industry can be exposed to these high levels of radiation; therefore, special precautions must be taken to protect these people.
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If a person receives too much raciation he will be injured. The degree of injury depends upon the amount of radiation received. The injured person will react in ore of three ways:
1.
There will be complete recovery with no side effects.
2.
There will be apparent complete recovery, but complications will set in years later.
3.
The most serious, death, can occur in a few days or weeks.
i Many of the delayed injuries result from the ingestion of radioactive materials into the body.
People can safe!y work with radiation because the allowable dose limits have been set at a level well below those known to cause injury. The greater majority of people working in the nuclear industry are exposed to radiation levels that are less than twice the natural background, and less than five percent of all the workers receive the maximum allowable radiation dose.
Before we get to the nitty gritty of this Guide on P.adiation Safety, let's take a a
look at the reason why we must go through this exercise. This reason is given in one brief statement.
Radioactive Materials Emit Energy Which Has the Power to Damage Living Tissue This one thought should be uppermost in your mind when dealing with radioactive materials and radiation.
Programs at IRT involving radioactive materials and radiation sources are reviewed by the Radiation Safety Officer and Radiation Safety Committee with respect to safeguards for minimizing the radiation exposure to the operating personnel. By following the instructions of the experienced IRT personnel and the Radiation Safety Protection methods described in this guide, you should be able to keep your radiation exposure to a minimum.
1 i
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- 2. PURPOSE t
l This manual is intended to make you aware of the hazaros of radiation and how to cope with it both physically and psychologically.
The subjects that are covered are: basic nuclear phenomens, interaction of radiation with matter, units of measurement, biological effects of radiation, the-operating characteristics of radiation detection equipment, the different types of radiation detectors, surveying techniques, radiation protection, rules and regulations, the Linac and Californium 252.
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3.' BASIC NUCLEAR PHENOMENA 3.1 ATOMIC STRUCTURE Modern atomic theory tells us that the atom has a diameter of 10-8 cm and consists of two parts--a small, dense, positively-charged central core called the nucleus and extranuclear orbital or planetary electrons which revolve about the nucleus in defiriite shells or orbits.. The negatively charged electrons are bound to the nucleus by coulombic (electrical) forces, and in the neutral atom there are :he same number of electrons as there are postively charged pe,rticles in the nucleus. The nucleus is of the order of 10~I3 to 10-12 cm in diameter, and is made up of two types of particles of about equal mass--the neutron and the proton. The neutron has no electric charge; the proton has a positive charge equalin magnitude but opposite in sign to that of a single electron. All nuclei have a mixture of protons and neutrons, the ratio of neutrons to protons being about 1:1 for lighter isotopes and increasing gradually as the n.as of the nucleus increate.
The structure of the atom determines the nature of the element or molecule. The number of protons in the nucleus (atomic number)' indicates the chemical property of the element. In order to make the atom electrically neutral there must be an equal number of electrons moving in orbit around the nucleus. It is the outermost ring of l
electrons that enter into chemical reactions. The total number of protons plus neutrons in the nucleus (atomic weight) determines the physical properties of the atom. All atoms containing 1 proton are hycrogen atoms even though they may contain 1, 2, or 3 neutrons; 8 protons constitute oxygen; 92 protons, uranium; mc. (See Figure 3-1.)
In order to get some idea of the relative size of the atoms total volume and the size of the nucleus and electron,let us expand the simplest atom, the hydrogen atom so that its electron moves in an orbit around San Diego, from Tijuana to Oceanside; then, the nucleus (the single proton) would be the size of a baseball and the electron would be only as big as a BB. With the atom containing so much empty spaa and with the subatomic particles being so small, it is easy to comprehend the ease with which these particles can travel through matter.
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Atoms with the same number of protons but O
containing a different number of neutrons are called O
I8 isotopest such as 0 0
0, these isotopes are 3
,3
,3 chemically identical. Isotopes can be either radio-NNNN 12 active or nonradioactive: of the isotopes:
C NNNN 6
13 14 14 12 13
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1 C
C
,C is radioactive, while C and C
- +++
g 6
? 6 are nonradioactive. There are relatively few natur-O ally occuring radioactive isotopes, most of them are man made.
When an element is heated in a flame or by means of an electric discharge, the electrons are
,,, M ln" g* 'n*c"i,d **f"
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g, excited to higher energy states and jump to a hider MI'Cd "5;ci,',, 73, nofjbit c: bit. When the element is removed from the flame, pr t ns determines the at mic number of the atom and its chemical proper-the electrons f all back to their original orbits and
$'g 5 The nu ber prot plus neu n,
release their acquired energy in the form of electro _
properties. The atom depicted above is oxygen 16 which as written,0 where 8 raagne:ic radiation of varying wavelengths.
The is the atomic number,16 is the atomic muss, and O is the element sy nbol.
orbits that the electrons can occupy are very dis-crete, however, and are fixed for each element.
Figure 3-1. The Atom Sodium for example has about 120 distinct energy levels that the electrons may occupy.
As mentioned before, the chemical properties of an element depend upon the number of protons in the nucleus with the chemical reactions actually taking place in the outer electron orbit. The various elements are arranged in a periodic system which is simply an arrangement of all the elements in order of their atomic number. Elements witn similar electron structures have similar chemical properties and form groups of related elements.
Just as chemical reactions involve a rearrangement of the outer electron shells of atoms, nuclear reactions involve a rearrangement of the protons and neutrons within the nuclei of atoms. Energy changes in nuclear reactions are of the order of millions of electron volts, compared with energies of only a few electron volts for chemical reactions. When a nucleus is excited, it, like the electron, also attains ~ very discrete energy levels. When the excited nucleus decays it emits radiations of certain definite energies.
6
3.2 RADIATION Radia' s is divided into two general types: particulate and electromagnetic.
Particul
- s the motion of small particles which have mass and, in most cases, an
~
elec' charge and which transfer energy from one point to another. These tiny portions of matter behave, in certain instances, like billiard balls; they are at times -
deflected from obstacle to obstacle losing energy with each encounter, until they are either captured or have exhausted all of their energy. The more common particles are alpha, beta, neutron, proton, electron, and positron. We will examine each of these in detail a little later.
Moving particles that experience a change in their velocity also experience a change in energy and mass. They receive energy when any force accelerates them and release energy when any force or atomic matter impedes their motion. Electrically charged particles can also be affected by magnetic forces. Particles, by transferring -
their energy to atoms, can cause ionization, light, and heat; therefore, they can be detected by using instruments such as cloud chambers, ionization chambers, photomul-tiplier tubes, or geiger counters.
3.3 PARTICUI. ATE RADIATION The ALPHA PARTICLE consists of two protons and two neutrons with a double positive charge. The alpha particle is actually the nucleus of a helium atom.
The BETA PARTICLE is identical in size and charge to the electron. The only diff erence between the beta particle and an electron is that the beta particle originates in the nucleus of an atom, not in the electron field surrounding the atom.
The NEUTRON is a particle with an atomic mass of one but with no net electrical charge. It is neutral.
The PROTON is a particle with an atomic mass of one and a positive electric charge of one. The proton has approximately the same mass as the neutron.
The POSITRON is a positively charged electron. It has the same mass but the opposite charge of the electron.
There are many more subatomic particles such as neutrinos, mesons, and muons but these are seldom encountered outside the field of high energy physics.
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3.4 ELECTROMAGNETIC RADIATION Electromagnetic radiation consists of varying electric and magnetic fields operat-ing at right angles to each other and. possessing both particulate and wave like characteristics. As a particulate, electromagnetic radiation is said to consist of small bundles of energy, called photons or quanta. A photon is a discrete quantity of energy having the properties ordinarily ascribed to particles. However, being a unit of radiant energy, the photon has momentum and always travels at the speed of light, whereas particulate radiation moves with a speed less than light. The energy of this photon depends upon its frequency or the wavelength of the electromagnetic radiation associated with it.
As a wave, electromagnetic radiation is propagated and measured in a manner characteristic of other waves (radio, light, sound, etc.). Wavelength is determined by the distance between troughs or crests of a wave; frequency is the number of waves per second.
Electromagnetic radiation includes gamma rays, x-rays, and cosmic radiation. All three of these rays are photons with short wavelengths, shorter than ultraviolet, that travel with the speed of light, conveying energy proportional to their frequencies (see Figure 3-2). Gamma rays originate in the nucleus of the atom, x-rays originate in the electron shell, and cosmic rays have extraterrestrial origins.
WAVELENGTH (CM)
FREouENCY (VIS/sEC) ENERGY /
?ssu$n$s Nn?n?
ERGS y
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/o, Figure 3-2. The electromagnetic spectrum 8-
- 4. INTERACTION OF RADIATION WITH MATTER 4.1 IONIZATION A fast moving particle or bundle of energy (photon) penetrating matter can be likened to a bowling ball crashing through a neat arrangement of bowling pins. As the -
fast energetic particle travels through matter, it abruptly disturbs the organization and balance of the atomic structure in the space through which it moves. lonization occurs when the electrical balance of an atom is disrupted. In its path through matter a charged particle can dislodge an orbital electron and drive it out of its orbit leaving behind a positively charged atom. The combination of the negatively charged electron and the positively charged atom is called an ion pair.
The dislodged electron is eventually captured in an orbit around another atom and the original atom will capture another electron. This can result in chemical changes, especially in biological systems.
Ionization is an energy transferring process. Besides direct ionization, ionization can occur by secondary means. Uncharged particles like neutrons can strike and excite the nucleus causing it to emit a charged particle such as a proton. This charged particle, by impacting the oribtal electrons in its path, will cause ionization.
Another form of secondary ionization occurs when electromagnetic radiation interacts with the nucleus of an atom. The atom absorbs the energy and becomes excited. It rids itself of this excess energy by throwing off one of its orbital electrons.
Secondary ionization also occurs after the initial liberation of the original electron. The liberated electron, as a charged particle, dislodges other electrons (secondary electrons) until its energy falls below the binding. energy of the impacted electrons. This can be a continuing process with the secondary electrons causing ionization throughout the space in which they travel.
The velocity, mass, and charge of the particle plus the conditions of impact will determine the amount of energy transferred to the electron. The initial imparted energy determines the amount of secondary ionization. The energy the secondary esectrons carry depends on the angle of collision and energy of the impacting electron.
i 9
---a a.
Low energy secondaries dissipate most of their energy in a short distance of travel from the point of energy transfer.
High energy secondaries will travel oeyond the ion cluster area and continue to produce ions in the delta area (Figure 4-1).
These high energy secondaries extend considerably the total ionization area affected by the original particle. Some of the energy transferred from the ionizing particle will be insufficient to produce ionization.
This energy is absorbed by the orbital electron and causes it to exist in an excited state.
Then, as more and more energy is absorbed, this excitation changes to ionization.
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DELTA AREA
/ /,
/
kkkkQkkkQk$$$
ION CLUSTER AREA IONIZATION PATH e :
PARTICLE V/MfM/MMM/MfMMfffM RT-20167 Figure 4-1. Ionization areas Some Definitions:
eV =
electron volt = the energy an electron would gain as it f alls through a potential diff erence of one volt.
kev =
Kiloelectron volts = 1000 eV MeV =
Million electron volts = 1,000,000 eV Specific ionization is the term used for the total number of ion pairs created per unit length of track by the particle. Specific ionization varies directly with the charge or mass of the particle and inversely with the speed or energy of the particle.
Total ionization is determined by the energy of the particle. In order to form a single ion pair, the ejected electron must pick up 32.5 eV.
In the foregoing we have discussed the ionization effect, which is the most common form of interaction. However, there are other methods by whicn radiation interacts with matter. These are described in the following paragraphs.
4.2 ABSORPTION OR CAPTURE An atom can absorb or capture particles or photons. By absorbing a radiation particle the atom can change to anotner element or to a ciff erent isotope of the same 10
element, or the atom's potential energy is increased. This change or energy increase must be dissipated by the emission of another radiation particle or photon. When a electromagnetic photon is absorbed, the atom's energy is increased which must be dissipated by the emission of a radiation particle or a lower energy photon. Some exa'mples of absorption:
(Y + 4Be')-.n + 2He" + 2He*
(n + ggNa23)~ Na - B + gamma ~12M8 24 gg 4.3 ANNIHILATION Annihilation is caused by a positron striking an electron. Both of these particles disappear and two gamma rays are created of 0.510 MeV each. High energy gamma rays can also cause annihilation, resulting in pair production.
4.4 SCATTERING Scattering generally occurs with neutron radiation.
The neutron strikes the nucleus of an atom and loses some energy which appears as recoil energy of the target.
The atom releases this energy by emitting some form of radiation. There are two types of scattering caused by neutrons: elastic and inelastic.
4.5 FISSION Fission is the splitting apart of the nucleus of an atom into two or more fragments, accompanied by a release of energy in the form of heat, light, and radition plus the release of a number of neutrons. Fission generally occurs only in heavy elements and is caused by the absorption of neutrons or very high energy gamma rays, i
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12-
- 5. THE NATURE OF RADIATION 5.1 ALPHA PARTICLES An alpha particle is a relatively slow moving heavy particle carrying a double positive electrical charge. An alpha particle is, in f act, the nucleus of a helium atom consisting of two protons and two neutrons. The alpha particles generally interact with matter by direct ionization, but they do not have great penetrating power; they are completely absorbed by a sheet of paper or by the outer layers of the skin. Because of this, alpha particles do not present serious problems if they are kept outside the body.
However, if they are ingested or inhaled, some alpha emitters such as radium, uranium, and plutonium tend to accumulate and remain in certain locations in the body where they decay and damage the surrounding tissue. Alpha particles also interact with matter by being absorbed into the nucleus of an atom.
Alpha particles generally come from elements with high atomic number (Bi element No. 83 or higher). The radioactive atom that emits an alpha particle loses two protons and two neutrons in the process. Its atomic number is thus decreased by two, and its mass number by four. For example, when an atom of uranium 235 (atomic number 92) emits an alpha particle, it changes to an atom of thorium 231 (atomic number 90).
235 231 92
~2He" (alpha) = 90 U
Th Alpha particle emission is usually accompanied by other types of radiation.
5.2 BETA PARTICLES A beta particle is identical in size and charge with the electron. Beta particles are both smaller and lighter than alpha particles and carry only a single negative electrical charge. Beta particles are much more penetrating but less ionizing tnan alpha particles. They are capable of penetrating up to one centimeter into the oody and 13
they can cause deep skin burns when exposure is excessive. Beta particles lose their energy or interact with matter primarily by direct ionization, and, as with alpha radiation, ingestion of beta emitters into the body may be quite harmf ul. Beta particles may also interact with matter by being captured into an orbit around a nucleus.
~
Beta particles originate in the nucleus of an atom not in the electron field surrounding the atom. When an atom emits a beta particle a neutron in that nucleus is changed into a proton. The atomic number of the atom is thus increased by one, while the mass number remains the same. The emission of an electron by strontium-90 (element No. 38) is an example of beta decay, and in this case the strontium-90 atom changes to yttrium-90 (element No. 39).
9 90 38
- Beta (S) = 39Y Sr Beta emission may occur alone, or it may be accompanied by other types of radiation.
5.3 POSITRONS Some atoms emit positively charged particles having the same mass as beta particles but with the opposite charge.
These particles are called positive beta particles, or positrons. Positrons interact with matter by ionization and annihilation.
When an atom emits a positron, a proton in the nucleus is converted into a neutron. The atomic number of the atom is thus reduced by one, but the mass number rgain remains the same. An example of positive beta decay is the isotope copper-64 (element No. 29) which decays to nickel-64 (element No. 28) by emitting a positron.
64./ (Positron) = 28 64 Cu Ni 29 Positrons are also created in the pair production method of gamma ray interaction.
5.4 NEUTRONS A neut on is a particle with an atomic mass unit of one, thus it is 1/4 the size of the alpha particle. The neutron has no electrical charge, and because of this, it is more highly penetrating than beta particles and is capacle of traveling completely through 14
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the body. Because the neutron has no electrical charge it does not cause ionization-directly; however, it does cause ionization indirectly. This indirect ionization is the result of the neutron striking the nucleus of an atom and dislodging a proton which causes ionization due to the positive charge that it possesses. The neutron loses some energy in this scattering process. The neutron travels through matter losing energy with each collision until it either escapes or reaches thermal energies at which point it is generally absorbed by an atom, sometimes making this atom radioactive.
The radioactive atom then decays and emits one or more other types of radiation.
Neutrons generally interact with matter by one.of three processes: elastic scattering, inelastic scattering, and absorption.
3.4.1 Elastic Scattering In the process of elastic scattering the neutron strikes the atom and merely bounces off in some direction with only a small loss of energy. The atom just recoils and emits the energy it has picked up as electromagnetic radiation. This process of recoil is called excitation. This elastic scattering by the neutron is generally associated with atoms having a large atomic mass.
5.4.2 Inelastic Scattering in the process of inelastic scattering the neutron losses a large amount of energy in each encounter.
There are two methods by which neutrons undergo inelastic scattering. In the first method, the neutron strikes the nucleus of a hydrogen atom (a proton) and with both particles being the same size, a " billiard ball" type collision occurs. The charged proton is knocked out of the atom and speeds off in some direction causing ionization, and the neutron, now greatly reduced in energy, moves off in another direction. In the second method of inelastic scattering the neutron actually enters the nucleus of the atom and another lower energy neutron is emitted along with some gamma radiation. This inelastic scattering by the neutron is generally associated with atoms having a small atomic mass.
5.4.3 Absorption The third method by which neutrons interact with matter is by absorption. In this process the neutron enters into the nucleus of an atom and generally makes the atom radioactive.
This radioactive atom decays by emitting one or more other types of 15
radiation. In most cases this absorption process is caused by neutrons of low energy called " thermal neutrons." This absorption process is associated with atoms of all atomic masses.
Neutrons can be obtained from four primary sources: the fissioning of Uranium 235 and Plutonium 239, from Beryllium, from neutron generators, and f' rom materials that fission spontaneously.
235 239 U and Pu will fission when they absorb a neutron and they will release 2 to 4 neutrons in the process. In order for this fission process to be useful it must be controlled. Nuclear reactors produce controlled fission and some experimental reactors can make the extra neutrons available for use. A problem with using reactor neutrons is that the work must be carried out at the reactor f acility.
Beryllium, which is element number four, can be induced to emit a neutron by striking the nucleus with a gamma' ray or an alpha particle. Beryllium neutron sources are made by mixing this material with certain radioactive materials, usually americium, plutonium, or radium. However, the number of neutrons produced by these sources is limited by the physical size of the source and the heat produced by the decaying radioactive materials.
Neutron generators produce neutrons by accelerating ions and causing them to strike a target that will emit a neutron. One type of neutron generator is the Crockoff-2 Walton neutron generator, which accelerators deuterium ions H striking a tritium g
3 target H which emits the neutron.
These neutron generators generally produce g
mono-energetic neutrons of very high energies that do not have wide spread application.
Spontaneously fissioning materials are radioactive materials that split apart (fission) without outside influence, releasing some neutrons and gamma rays in the process. These materials are the most versatile of all the sources of neutrons. The most useful of the spontaneously fissioning materials is californium 252 (Cf-252).
Cf-252 emits 3 or 4 neutrons with each fission; the source can be quite small in size but still produce a large neutron flux.
5.5 GAMMA RAYS AND X-RAYS Gamma radiation is electromagnetic radiation similar to x-rays, radio waves, and visible light. This type of radiation is emitted in small units called photons. Gamma ray emission from the nucleus of an atom does not change the nucleus as do alpha and beta emissions. However, gamma radiation is generally accompanied by the emission of some form of particulate radiation. X-rays are also electromagnetic radiation and are 16
w similar to gamma rays. Gamma rays normally originate in the nucleus, while x-rays originate outside the nucleus and generally have less energy than the gamma rays.
Gamma rays and x-rays differ from ordinary visible light in that they are much more energetic and therefore more penetrating. Gamma rays and x-rays lo::e energy by causing ionization by three very distinct methods: photoelectric effect, Compton scattering, and pair production (see Figure 5-1). The photoelectric effect and Compton scattering cause direct ionization out pair production causes indirect ionization. These are described in the following paragraphs.
E LOW - EN E RGY ELECTROMAGNETIC RAOIATION ABSORBERS OF HIGH ATOMIC WEIGHT PHOTOELECTRIC EFFECT ELECTROMAGNETIC RAOIATION MEDIUM-ENERGY OF LONGER ELECTROMAGNETIC WAVE-LENGTH Al8Eng RADIATION A8SORSERS g
OF ANY ATOMIC WEIGHT COMPTON EFFECT TR H HIGH - ENERGY ELECTROMAGNETIC RADIATION CJCOX5 e,C A8SORSERS
- I404 OF HIGH ATOMIC WEIGHT PAIR PROOUCT'ON Figure 5-1. Interactions of electromagnetic radiation 5.5.1 Photoelectric Effect The photoelectric effect is an absorption process which takes place with photons of low energies. A gamma photon interacts with an orbital electron of an atom ana 17
transfers all of its energy to this impacted particle, either ejecting it from the atom or raising it to an unoccupied position in another shell. The absorption of photons by the photoelectric effect varies with the gamma energy. The probability for the photo-electric eff ect is larger for heavy elements.
5.5.2 The Compton Scattering For gamma rays greater than 1 MeV, where the photon energy is much greater than the binding energy of the electron, another process--Compton Scattering--
becomes important. This process is a combination of scattering and absorption in which the gamma photons behave like small particles and undergo billiard-ball type collisions with electrons. The electron absorbs some energy and recoils upon collision with the gamma ray, or is ejected from orbit; the photon loses only a part of its energy in the collision. Since this process does not completely absorb the interacting gamma ray, it travels on causing further ionization.
5.5.3 Pair Production At higher gamma ray energies, a new and rather startling phenomenon known as pair production takes place. When a high energy gamma ray enters the charged field in the vicinity of the nucleus, the gamma ray dissappears and a pair of electrons is created. One of these electrons is the ordinary type but the other is a positive electron, or positron. In pair production, all the gamma energy is used up and goes into creating the electron-positron pair and imesting kinetic energy to the particles which now travel through matter causing ionization. A gamma ray with at least 1.02 MeV of energy is required for this reaction to take place. Pair production causes indirect ionizai'on and in this reaction energy is converted into matter.
5.5.4 Gamma-N Reaction A fourth method by which gamma rays interact with matter is a scattering method that is not generally considered because an extremely energetic photon is needed. But we mention this method because it occurs regularly at the Linac. When a gamma ray with energy greater than 10 MeV strikes the nucleus of an atom it can dislodge a neutron from that nucleus. This is called the gamma-n reaction.
18
5.6 PROTONS A proton is a particle with an atomic mass of one and a single positive charge.
This charge is equal to and opposite the charge of the electron. Protons are slightly more penetrating than alpha particles but they do not penetrate more than 2 mm into the body.
Protons lose their energy primarily by direct ionization.
The protons originate in the nucleus of the atom. When an atom loses a protor., both its atomic number and atomic weight are decreased by one. There are very f ew proton emitting elements.
5.7 SUMM ARY OF RADIATION INTERACTION 5.7.1 Alpha Particles Alpha particles generally interact by ionization but in some cases they interact by absorption into the nucleus.
5.7.2 Beta Particles Beta particles interact by ionization and by capture into an orbit around a nucleus.
3.7.3 Positrons Positrons interact by ionization and by annihilation when striking an electron.
3.7.4 Neutrons Neutrons interact by scattering and by absorption into the nucleus.
5.7.5 Gamma and X-Rays Gamma rays and x-rays interact by causing direct and indirect ionization.
5.7.6 Protons Protons interact by ionization.
19
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- 6. UNITS OF RADIATION MEASUREMENT
6.1 INTRODUCTION
TO RADIATION MEASUREMENT UNITS The Roentgen was the first radiation dose unit used in radiology and it was defined for a specified electrical charge produced in a volume of dry air by X or gamma radiation. Since this unit applied only to air, it is not generally applicable to other materials, nor is it applicable to other types of radiation. In order to produce a more useful unit of radiation, the Roentgen Equivalent Physical (Rep) was defined on the basis of energy absorption in a gram of sof t tissue. The Radiation Absorbed Dose (RAD) is a modernized REP unit and it defines the RAD as the deposition of 100 ergs of energy per gram of tissue.
Because we are primarily concerned with the effect of radiation on man, and man is not all sof t tissue, and there are other types of radiation besides X and gamma rays, another unit of measurement had to be defined.
Other types of radiation, each releasing 100 ergs in sof t tissue, will produce a biological effect that is quite different from the effect produced by X or gamma radiation releasing the same amount of energy.
Each type of radiation was tested to determine its effect upon biological material and a Relative Biological Effectiveness (RBE) or Quality Factor (QF) number was derived.
In order to determine the true biological dose, the radiation dose measured in Rads, is multiplied by the RBE or QF to yield the REM-Roentgen Equivalent Man.
The RBE or QF is dependent on the Linear Energy Transfer (LET) of the ionizing radiation. Particulate radiation such as neutrons, alpha particles, protons, etc., will deposit more energy or cause more ionization per length of unit travel than X or gamma rays, and naturally this higher concentration of ions in a small space will cause greater biological change or damage, resulting in the higher RBE or QF number.
21
6.2 DEFINITIONS OF RADIATION UNITS 6.2.1 Roentgen (R)
The Roentgen was defined as that amount of X or gamma radiation that will produce one electrostatic unit of charge, of either sign, in one cubic centimeter of dry air at STP. This is equivalent to the deposition of 83 ergs of energy per gram of dry air.
6.2.2 Roentgen Equivalent Physical (REP)
The REP was determined to be that amount of X or gamma radiation that will deposit 93 ergs of energy in one gram of sof t tissue.
6.2.3 Radiation Absorbed Dose (RAD)
The RAD was defined as that amount of any type of radiation that will deposit 100 ergs of energy per gram in any material.
6.2.4 Relative Biological Effectiveness (RBE), Quality Factor (QF)
This is a multiplier number used to determine REM. Some RBE, QF numbers are:
X-R ay............
1 G am m a...........
1 Beta 1
Neutron (thermal).......
5 Neutron (fast) 10 Alpha............
20 6.2.5 Roentgen Equivalent Man (REM)
The REM is determined by the following formula: REM = RAD X.RBE (see Figure 6-1).
. 6.3 CURIE (Ci)
The Curie defines the quantity of radioactive material present. The curie is not a measure of weight, it is a rate-of-decay term. A curie is the quantity of radioactive 10 material that decays at a rate of 3.7 x 10 disintegrations per second.
By this definition:
22
235 46,000 grams U
1 curie
=
226 1 curie c=ce I gram Ra
=
60 0.003 grams Co 1 curie
=
BOOT ftSSWC 6.4 RADIOACTIVE DECAY ROENTGEN ENtmov Radioactive decay is the process by which excited atoms lose their excess
==**'
'c.
energy. In this process the atom losses its saoc. cat EFFECT excess energy by emitting some radio-active particle along with some form of electromagnetic radiation.
Some radio-Figure 6-1. Defining the Roentgen in terms Ehec"t8' active atoms are pure beta emitters and i
some are pure gamma emitters. Most radioactive atoms continue to decay until they reach a stable state (see Figure 6-2). Pure gamma emitters, however, will not reach a stable state but the emitted gamma ray gets so weak that it cannot be measured.
6.5 HALF LIFE Another radiation term is half life (t ) which is defined as the amount of time g
required for one-half of the radioactive material to decay. Each radioactive isotope
.has its own half life. Some examples:
226Ra 1620 years
=
252Cf 964.26 days
=
64Cu 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br />
=
16N 7 seconds
=
23
A70 wi0 % UMBER 8e l82l83 Sa SS 86 $ 87 48 89 l 90 lS6 92 l
l.
.0 I 238
/
'h h h 234 s,s 230 Q
ni,,f o
,226
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o E
- Orm
/
s%
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2g.<
p-s, 284 h
210 206 Ph lBa Po f Ag Rt Ac Th Pg
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URANIUM g
PROTCACTINiyu wt THORIUM ACTihiWM 4 ADIUM 8'00"
8ISMuTM gg
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LEAD g%
c tho 0F SERIES Figure 6-2. Radioactive decay scheme for uranium 238 24
- 7. BIOLOGICAL EFFECTS OF RADIATION 7.1 INTERACTION OF RADIATION WTTH BIOLOGICAL SYSTEMS Radioactive material emits energy which has the power to damage living tissue, either directly or indirectly. Directly the radiation can alter the structure or electrical charge of the molecule, indirectly the radiation can produce peroxides or other oxidizing agents that damage the living cell.
The effects of radiation upon biological systems may be summarized as follows:
1.
Manner.
The manner in which radiation affects cells may be direct or indirect and localized or remote from the original point of injury.
2.
Time. The effects may be immediate or delayed.
3.
Type. The same type of radiation may produce different types of structural damage and/or functional changes in the cell or tissue.
4.
Effectiveness. The radiation effects may be reversible or irreversible.
7.1.1 Direct Method Biological cells are made up of a large number cf molecules which in turn are made up of a large number of atoms. These atoms are joined together at the outer electron rings and the molecule is generally formed into long chains. If a radiation particle or photon strikes an electron joining two atoms and knocks it out of orbit, the two atoms will separate and break the molecular chain. The radiation may also strike an inner electron or the nucleus itself and excite the atom, changing its electrical charge and again causing a break in the molecular chain. When the molecule breaks in two or more parts, some of these fragments are charged and some are not. Those that are charged will quickly react with adjacent atoms and molecules. Those that are not charged may, after a time, react with the new molecules formed by the charged f ragments. The breakup of the molecule is harmful to the cell and can inhibit its normal operation. Therefore, the molecular fragments must be disposed of and a new molecule constructed in order for the cell to function properly.
25 i
7.1.2 Indirect Method Since the living cell is mostly water, radiation absorbed in this water alters the bonds between the hydrogen and oxygen atoms and produces a variety of free radicals such as f ree hydrogen, f ree oxygen, hydroxyl radicals (OH), hydrogen dioxide (HO )' ""d 2
hydrogen peroxide (H 0 ).
These powerf ul chemicals can break down the complex 22 protein molecules in the cell (see Figure 7-1). Some of these protein molecules make up the cell wall and if this wall is breached some of the cell products can flow out, depriving the cell of needed nutrients thus damaging it.
Another type of protein molecule is the enzyme. Some of which control the rate of cell division.
These enzymes are easily damaged by oxidizing agents and, as a result, the rate of cell division is altered. This alteration of cell division may take different forms: the parent cell may divide too soon, producing daughter cells that are immature and unable to function properly; the cell may divide and produce daughter cells that are genetically different from the parent; or the parent cell may not divide at all, and when it dies there is no replacement to take over its function (see Figure 7-2).
H 0-2 A
ES H,0+
O:f H+
0-SOURCE OF WATER RADIATION OH-OH~
"2 2
H0 H0, H,0, H+
2 H0 3
-/
BREAKDOWN PRODUCTS FROM
\\
H,0+
l r
IRRADIATION OF WATER N
N
/
N N
H0,
\\
I g
DIAGRAM OF MOLECULAR BREAKDOWN
\\
CAUSED BY IRRADIATION
\\
RT-20166 BREAKDOWN OF MOLEC1ES BY IONS Figure 7-1. Molecular breakdown caused by radiation and water ions 26
W b
FARENT CELL NORMAL CELL p-4, IRRADIATED IRRA0!ATED CELL h
CELL DIV ION FAaENT CELL CELLS INC/PABLE O LIFE g@
0 CEATw rotLewtNs Divts:0N Or TwE CELL DIVISION IRRADIATED PARENT CELL DAUGwTER CELLS PRODUCTION OF AN ABNORMAL CELL BY RADIATION NORMAL CELL DIVISION RT-20165 Figure 7-2. Production of abnormal cells ley radiation 7.2 MAJOR TYPES OF BIOLOGICAL EFFECTS The two major types of biological effects of radiation are genetic effects and somatic eff ects. Genetic eff ects are those that are passed on to future generations and somatic are those experienced by the individual.
7.2.1 Genetic Effects The genetic effects are caused by radiation which can alter genes and produce mutations whicn may show up in future generations. You will notice the use of the words "can" and "may." These words are chosen deliberately to indicate the uncertainty involved in discussing and understanding genetic effects. The proolem arises from the f act that we cannot determine the exact cause of any specific mutation. A mutation may or may not have been caused by radiation and if it was caused by radiation, it is difficult or impossible to pin point the source of the ray On the other hand, it cannot be positively stated that even very small doses of radiation do not cause genetic effects.
27
Each cell in the human body contains 23 pairs of genes or chromosomes that determine each individuals inherited characteristics such as hair colcr, eye color, size, and so on. One chromosome chain is contained in the egg and the other is contained.in the sperm cell. When the egg and the sperm are joined the 23 pairs of genes are formed. If a chromosome chain in an egg or sperm cell is broken, a mutated gene will result. Most mutated genes are recessive an'd the other gene of that pair will be dominant and will determine that specific characteristic. If two recessive or mutated genes are joined the result. will be a mutated characteristic.
Most mutations are undesirable and generally are lost because the individual cannot reproduce and transmit the mutation, or, in most cases, the mutation is so slight that its effect is lost in future generations by being literally bred out of existence. The spontaneous mutation rate for man is about one in 50 births. The amount of radiation needed to double this mutation rate to two in 50 births is of the order of 6 to 30 Rem per year. Genetic effects are the result of irradiation of the reproductive organs only.
7.2.2 Somatic Effects The somatic effects of radiation are those experienced by the individual. They are the most obvious and are of primary concern in radiation protection. Somatic effects can be either acute or delayed. Acute effects are seen immediately and cause prompt sickness or death. The delayed effects of radiation are an increase in the probability that an individual will develop leukemia or cancer and a shortening of the expected life span.
The severity of the somatic effects are controlled by a number of f actors.
I 1.
Living cells begin to repair themselves as soon as damage occurs, so the body can keep pace with a certain amount of radiation that is administered continucusly.
i 2.
A person in good physical condition can recover from a certain radiation dose more quickly than a person in poor health.
3.
The type and energy of the radiation also controls the amount of damage that occurs. Beta particles and low energy X-rays do not penetrate more than a half inch into the body and will only damage the skin. High energy gamma rays, X rays, and neutrons can penetrate all the way through the body and cause damage all along the way.
28 i
I
i r
4.
Another factor that controls somatic effects is the area of the body or organ that is exposed. A small area of the body or certain organs could be exposed to very high doses of radiation and not cause permanent damage to the individual. However, if this same dose were delivered to a major portion of the body, the individual could die.
5.
Two other controlling factors are the total dose and exposure time. If a person were to receive a dose of 500 roentgens in one day he would have less than a 50 percent chance of living. If this same dose were administered over
~
a period of two months the person would have a 90 percent chance of almost complete recovery.
7.2.3 Specific Organ Response to Radiation The various organs and tissues in the body differ in their response to ionizing radiation. This response difference is called radiosensitivity. Tissues containing cells that are rapidly reproducing and are relatively nonspecialized are the most radiosensi-tive, whereas cells that are highly specialized and reproduce slowly have the least amount of radiosensitivity. This information is useful as a method of determining the quantity of radiation received on the basis of the biological effects. A list of important cells and organs in order of their radiosensitivity is as follows:
l.
The tissues of t,he spleen, lymph nodes, etc., which produce the white blood cells, are the most sensitive to radiation, with the white blood cells of ten being used as the first indicators of radiation injury.
2.
The w. se blood cells formed in the bone marrow and believed to combat infection, are also highly sensitive to radiation.
3.
The gonads, the bone marrow, the skin, the alimentary canal, and hair follicles are the next most sensitive organs.
4.
The adrenal gland and thyroid gland are next on the list for sensitivity to radiation.
5.
The alveolar cells of the lungs, which absorb oxygen from the air and release carbon dioxide from the blood, are fairly high on the radiosensitivity scale.
6.
The urinary tract, the liver, and the gall bladder are intermediate in the order of radiosensitivity.
29
7.
The eyes are also intermediate in their sensitivity to gamma radiation; however, they are highly sensitive to neutron radiation.
3.
Brain cells and muscle cells are both fairly insensitive to radiation.
9.
The bone cells and the nerve cells are the least radiosensitive.
7.3 BIOLOGICAL EXPERIENCE OF RADIATION DAMAGE The biological experience on which our evaluation of radiation damage is based comes from various sources.
A chronic or continuous radiation exposure causes changes such as dryness of nails-and skin, epilation (loss of hair), obliteration of tinger prints, persistent ulcers, especially skin ulcers (sores that will not heal), and skin cancers. These conditions were seen in a number of the early experimenters and radiologists. Though it has been difficult to determine the exact doses received by these people, it has been calculated that the doses involved were of the order of several hundred millirem per day received over a period of years.
The damage caused by these chronic doses tends to be permanent. Surprisingly the damage caused by an acute dose of up to several hundred Rem is often reversible. In other words, after a certain recovery period there is no permanent signs of radiation damage.
During World War I when luminous dials were first introduced, many of the individuals who painted the dials ingested radium when they tipped their brushes with their lips. This radium lodged in their bones and in some cases bone cancers developed a number of years later. Af ter autopsies were performed on the victims, it was possible to determine the amount of radium present and to relate this to the amount of damage observed. This information applies specifically to alpha emitting materials whose chemistry causes them to be deposited in the bones. It is interesting to note that there I
were no reported cases of leukemia in these dial painters, even though leukemia is usually thoughi of as a radiation induced disease uf the blood forming tissue in the bone marrow.
Quite a bit of information is being ythered from the survivors of the Hiroshima and Nagasaki bombings. One of the effects being observed is increase in the number of cases of leukemia and tumors. No mutations have been seen as yet. Since mutations are recessive it will take some time before they show up. Maybe in the fif th or sixth generation two persons with recessive genes will mate and produce a true mutant.
r-.-
__.--___.,-.--.--x.-
In addition to the above sources of human information there is a large amount of information being gained from animal experiments. The most useful animals are dogs, monkeys, and swine. These animals have been used to determine the LD50 and LD10'O-deses. Because these animals have a much shorter life span than man, it is difficult to -
conduct experiments with low doses of radiation and obtain useful data applicable to man.
The data obtained from various sources indicates that man can expect a 5 to 10 day loss of life expectancy for every roentgen of full body exposure.
7.4 RADIATION EXPOSURE LIMITS Quite soon after the discovery of radium and x-rays, the people working with these materials found that they were suffering ill effects af ter being exposed to these mysterious rays. One of the major effects they observed was that their hands and nails were turning red and dry. Radiologists, scientists, and doctors realized that radiation was harmful, so in 1902 the first recommendations for restricting radiation exposure were made. The recommendation was to limit expost:re to less than that amount of radiation that would fog film. This dose was about 1 R per day or 360 R per year.
In 1925 the second recommendation was made to limit exposure to less than one-one hundredth of the erythema dose (that amount of radiation that will redden the skin).
This dose was determined to be about 4 R per month or 48 R per year.
The third recommendation was made in 1936, and this recommendation was to limit exposure to less than 100 mR per day,2 R per month, or 24 R per year.
In 1950 the fourth recommendation was made to limit exposure to 300 mR per week or 15 R per year.
The most recent recommendation, which was made in 1957, is the limit that is presently observed. The limit for whole body occupational exposure is 1.25 Rem per calendar quarter, or 5 Rem per year. Exposure to the general population is limited to 0.5 Rem per year from industrial sources.
This value of 5 Rem per year is based on the criterion that a person receiving this dose beginning at age 18 and extending through his working lifetime, will suffer no observable ill effects. This value does not represent a threshold dose above which injury will definitely occur but neither should it be assumed to offer no risk at all.
Recently the Regulatory Agencies have adapted a new and rather ambiguous level of exposure, which is that' personnel radiation exposure must be kept "as low as 4
3'
reasonable achievable." The regulatory agencies have not defined " ALAR A" other than stating that efforts to reduce personnel exposures must be pursued constantly.
7.5 BACKGROUND
RADIATION EXPOSURE The annual background radiation dose a person receives depends on where he lives and works, what he eats and drinks, how he travels, and how of ten he sees his doctor or dentist.
The following list gives some annual radiation dosages of radiation from various sources:
Cosmic radiation at sea level 40 mrem / year
=
Each additional 100 feet of elevation 1 mrem / year
=
Living in a wood house 35 mrem / year
=
Living in a concrete house 50 mrem / year
=
75 mrem / year Livir.g in a brick house
=
Working outdoors 8 hr/ day 15 mrem / year
=
25 mrem / year Food and water
=
Each 1500 mile jet flight 1 mrem
=
Each chest X-ray 100-200 mrem
=
Each dental X-ray 20 mrem
=
7.6 EFFECTS OF. WHOLE-BODY DOSES RECEIVED IN A SHORT TIME People occupationally exposed to radiation may receive up to 5000 mrem per year. A dose of 10,000 mrem received over a period of a few hours can produce a lowered sperm count in males but no observable effect in females. A dose of 50,000 mrem received in a 24-hour period ca cause observable changes in the blood for both males and females.
Dose in Rems 50 No obvious effect except minor blood changes.
100 Vomiting and nausea for about one day in a small percentage of exposed individuals. Fatigue, but no serious disability.
200 Vomiting and nausea for about one day, followed by loss of hair, loss of appetite, hemorrhage, and other symptoms of radiation sickness in about 50 percent of individuals. No deaths anticipated.
32
300 Vomiting and nausea' in nearly all individuals on first day, followed by loss of hair, loss of appetite, fever, hemorrhage, nosebleeds pallor, diarrhea and other symptoms of radiation sickness. About 20 percent deaths within two to six weeks af ter exposure;. survivors convalescent for about three months.
450 Vomiting and nausea in all individuals on first day followed by other symptoms of radiation sickness. About 50 percent deaths within one month due to secondary infection and damage to the bone marrow, blood system, and lymph system.
700 Vomiting and nausea in all individuals within four hours of exposure fol' awed by other symptoms of radiation sickness.
Up to 100 percent deaths, again due to secondary infection and damage to the bone marrow, blood system, and lymph system.
1,000 Vomiting and nausea in all personnel within, one to two hours.
Probably no survivors from radiation sickness.
10,000 No survivors, 50 percent deaths in four days due to intestinal damage.
1,000,000 All die within one day due to nerve damage.
In general, treatment of injury from radiation is largely symptomatic in nature; in other words, treat the symptoms rather than the disease by administering antibiotics, bowellubricants, intravenous feedings, blood transfusions, and bone marrow transplants as needed. The symptoms are summarized in Table 7.1.
Table 7.1. Summary of Clinical Symptoms of Severe Radiation Sickness Tarne af ter Survaval improoante Survival Posuble Survival Probanle raposure (700 R or more) 030 R to 300 R)
(230 R to 100 R) ist day Naosea, vomiting, and diarrhea Nausea, vomstang, and daarrhea Posuble nausea, vomiting, and an farst f ew hours an first f ew hours daarrhea on first day ist ween No defanate symptoms an some cases (latent period) l Diarrhea, hemmorrhage, pur-M M tm Wm pura, anflammataan of moutn and peraod)
No definite symptoms (latent throat, f ever period) 2nd ween Rapid emaciation, death (mor.
Epilation, loss of appetite, and tality - probably 100%)
general malasse,iever i
Hemorrhage, purpura, petechsae, Epalation, loss of appetite and nosebleeds, pallor, anflammation malaise, sore throat, bem-3rd week of mouth and throat, daarrhea,
- orhage, purpura, petechase, emaciataan
- pallor, daarrhea, moderate emaciatson Death in most sersous cases, 4th week (mortality - 30% for 430 R)
Recovery likely in aoout 3 months unless complicated by prevsous poor health or super-imposed anjuries or anf ections.
Noter it as daliscuit to receive a dose of 'O R or more. norkang around a Nuclear Reactor or an Accelerator at could happen, but generally only if a pes sor, egnored the saf ety rules. Workang with a radioactive source a person would have to remove the source frorn its thKid and hold an close prontmaty to the body, and that would be suacade.
33
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i
\\
- 8. PRINCIPLES OF RADIATION DETECTION AND MONITORING TECHNIQUES Radiation detection may consist of different types of operation:
Detection Verif y the presence or absence of radiation.
Monitoring Related to a time-dependent observation, which is the deter
- minations of the radiation dose rate in mR/hr, or to establish safety standards of exposure.
Analysis Related to identification of the radiation source and its energy distribution or spectra, and, in some cases, determination of time sequence of events.
Dosimetry The determination of the type and energy of the radiation as related to the absorption of this energy in matter and especially in body tissues.
All of these operations are carried out at IRT but only detection, monitoring and dosimetry will be discussed in this section.
Five geaeral methods for detecting radiation will be discussed here:
1.
lonization detectors which use an electric tield to collect ions formed by radiation in a gas.
2.
Scintillation detectors that produce light pulses which can be amplified and counted.
3.
Secondary particle detectors that are used to detect neutrons.
4.
Emulsions or photographic film that respond to radiation much as they do to light.
5.
Thermoluminescent dosimeter crystals that are altered under radiation exposure and then release light when heated.
35
8.1 IONIZATION DETECTORS The most common Health Physics survey instruments use the ionization principle
~
to detect and measure raciation.
These instruments include ionization chambers, proportional counters, and Geiger counters. The graph in Figure 8-1 will help to explain i
how and why the va-ious ionization instruments operate. By applying a variable voltage to the central wire :n the detector and measuring the current. coming out of the detector, a graph with the following si.: definite regions will result.
l l
I I
i l
l I
I I
i l
l l
l 1
I I
I I
l l
l 1
l l
l 1
9 I
II l
III I
i 3
I IV y
i VI l
IONIZATION l PROPORTIONAL M
IONS LIMITED
_RECOMINE !
l G!EGER-MEULLER lCONTINUGU REGION REGION lPROPORTIONA REGION DISCHARGE -
7 I
l REGION REGION l
l I
l l
8 1
I s
1 I
i i
l 3
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l l
i l
1 l
l 1
l l
l I
l l
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i 200 800 1000 RT-20219 VOLTAGE Figure 8-1. Ionization variation with applied voltage Region 1 - The Recombination Region. In this region the current rises rapidly as the voltage is increased; however, because the ions are moving so slowly many of them are recombined before they can be collected and measured.
Region II - The Ionization Region. In this region th'e ions being produced are moving so rapidly that very f ew can recombine and essentially all ions are collected and measured. The output current within this region is relatively unaffected by increases or decreases in the voltage.
36
Region Ill - The Proportional Regic7. In this region the velocity of the ions is so great that they cause secondary ionization by collision with other orbital electrons.
Thus the current rises due to the additional ion pairs. This secondary ionization is called gas multiplication. For a given voltage in this region the gas multiplication is constant and thus the output current is proportional to the number of ion pairs initially formed by the radiation.
Region IV - The Limited Proportional Region. No detectors operate in this region.
Region V - The Geiger-Muller Region. In this region the secondary ionization or gas multiplication is so high that a virtual cloud of electrons surrounds the central electrode.
The current output i's no longer proportional to the voltage and all information concerning the number of the initial ion pairs is lost, also, the output current is relatively unaff ected by voltage changes within the region.
Region VI - Continuous Discharge Region. In this region the voltage gradient is so high that any stray electron causes a complete avalanche of electrons.
8.1.1 Ion Chambers Although all of the methods of detecting radiation so f ar described involve ionization measurements, the detector operating in Region 11 is generally ref erred to as an ion chamber. The chamber consists of an enclosed cavity filled with a counting gas which is generally dry air. The ion chamber is normally used as a dose-rate meter that integrates the total charge collected on the central electrode in a given time, reading in mR/hr. By constructing the chamber walls of low atomic weight materials and using dry air as the counting gas, this type of instrument can be calibrated in Roentgens for x-rays, gamma rays, and beta particles. Although the ion chamber will detect all types of radiation except neutrons, it is generally used to monitor for only x-rays, gamma rays, beta radiation, and positrons.
There are a number of types of ion chamber instruments, at IRT we use the Juno, the Victoreen 440RF, Victoreen 392B, and the Victoreen 470A.
3.1.2 Proportional Counters Proportional counters were used as detectors for ionizing radiaton as early as 1910. Since the output currents in the proportional counter is dependent upon the applied voltage, the maintenance of a stable high voltage supply is much more important than in either the ion chamber or GM counter. In the proportional counter 37
I each electron freed by ionizing radiation will move toward the central electrode and as it gets closec, its speed will increase and multiplication will commence, producing a small cluster of ions in that particular region. This cluster of ions will be quickly swept away by the voltage gradient and measured as a pulse.
Since each type of radiation will produce a different number of initial ions, the output current is different for each type of radiation, alpha particles produce large pulses, beta parP medium pulses, and gamma, or x-rays-small pulses. Thus with the proper discriminator a proportional counter can detect and count only _ that type radiation that is of interest. Also, the proportional counter can discriminate between varying energies of the same type of radiation.
Most proportional counters use argon, methane, or helium as the counting gas. By flowing the counting gas through the detector continuously, it is possible to place the sample inside the detector, thus eliminsting the need for a window. This is particularly important in measuring low-energy radiations which would otherwise be absorbed in passing through a window. Proportional counters are generally used as pulse counters.
8.1.3 Geiger Cotaters The Geiger-Muller detectors, or more commonly " Geiger counters," have been used as radiation detectors since the early 1900's.
In the Geiger counter the amplification of the original icns is much higher than in the proportional counter as a result, a virtual cloud of positive and negative ions surrounds the central electrode.
The negative ions are quickly swept,away as a current pulse leaving the sluggish positive ions surrounding the electrode.
This blanket of positive ions destroys the voltage gradient between the central electrode and the chamber wall rendering the tube inactive or " dead" until they drift away or recombine with free electrons. This " dead time" can be quite long and during this time if another radioactive particle or photon should enter the tube it would not be counted.
This " dead time" is the major disadvantage of the Geiger counter. Various devices have been used to reduce this
" dead time." The most common is the use of an external resistance that causes the voltage to drop across the detector electrodes which promptly discontinues the gas amplification. In addition, Geiger tubes are filled with a halogen gas such as bromine or chlorine which acts as a quenching agent that recombines the ions quickly.
The Ceiger counter is generally used as a pulse counter to detect low levels of j
radiation. If, however, the source used to calibrate the instrument has characteristics 38 i
similar to the radiation being monitored, the Geiger counter may be used as a dose-rate meter with good accuracy.
8.1.4 Summary Ionization chambers can be used to detect all types of radiation except neutrons.
They are generally used as dose-rate monitors for x-ray, gamma, and beta radiations.
Using air as the counting gas they can be calibrated in roentgens.
Proportional counters are generally used as pulse counters. Because the output pulse is proportional to the incident radiation, the proportional couner can discriminate between the various types of radiation and varying energies of the same type. of radiation.
The Geiger counters are the most versatile of the ionization instruments. They can be designed to detect low levels of alpha, beta, or gamma radiation, or a combination of radiations. They possess a high sensitivity, come in a wide range of sizes and shapes, have simple circuitry, and are rugged, portable, and inexpensive.
8.2 SCINTILLATION DETECTORS Certain materials have the ability to fluoresce or give off a pulse of light when struck by a radiation particle or photon. These materials are called phosphors. When struck by radiation the phosphor is raised to a higher energy level which it immediately dissipates by giving off a pulse of light. Phosphors are generally solid crystals, but they may also be liquids or gases. The most useful phosphors are the organic crystals anthracene, stilbene, and transstilbane; the inorganic crystals sodium-iodide activated with thalium, zinc-sulphide activated with silver, and germanium activated with lithium; and finally the organic liquids xylene and terphenyl.
A phosphor, to be useful, requires some device that can detect and measure the light flashes, and this device is called a photomultipfler tube. There is a wide variety of photomultiplier tubes but they all operate in essentially the same manner. The light 4
f rom the phosphor strikes the photocathode whicn is a layer of semitransparent material that emits electrons when struck by light photons. The electrons are emitted f rom the inside surf ace of the tube. An electrical grid system attracts and focuses the electrons onto the first dynode. The electrons pass from one dynode to the other, increasing the number of electrons at each stage. The total current amplification is well up into the millions.
39
\\
Scintillation survey instruments are extremely sensitive and are generally used to monitor very low levels. of radiation. In the laboratory, scintillation instruments are -
extremely useful tools. The energy of the radiation striking the phosphor determine the number of light photons produced and, in turn, the number of light photons striking the photocathode determines the size of the current pulse out of the photomultiplier tube.
Thus the current pulse is proportional to the energy of the radiation. By coupling the scintillation detector to a pulse-height analyzer, unknown radioactive isotopes can be rapidly and positively identified.
8.3 SiiCONDARY PARTICI.E DETECTORS These devices are used mainly to detect neutrons. Since neutrons are electrically neutral, they do not cause ionization oirectly. However, neutrons do interact with atoms and, as a result, can cause the atom to relea<e some type of ionizing particle.
These types of detectors include proton recoil counters, fission counters, and BF3 detectors.
Proton recoil counters are used to detect fast neutrons. In one type of c'etector an ionization chamber is pressurized to a few atmospheres with hycrogen gas. When a fast neutron strikes the nucleus of the atom, the proton is knocked loose. This proton then causes ionization as it tra.vels through the chamber. The ions are collected by the electrodes and a current pulse is produced, indicating the presence of a neutron.
Another type of proton recoil counter is simply an ionization chamber surrounded by hydrogeneous material such as paraffin. In this detector the scattered protons enter the ionization chamber, causing ionization and a resultant current pulse.
Fission counters are proportional counters that are lined inside with a fissionable 235 239 material, such as U or Pu. These instruments detect only thermal neutrons. The thermal neutron will be captured and cause the U or Pu atom to fission. The resultant fission fragments are highly ionizing and will cause a large current to be produced by the detector tube.
BF detectors are proportional counters filled with a Boron trifluoride gas. Boron 3
is used because it has a very high prooability of capturing thermal neutrons. When a thermal neutron enters the detector chamber, it is readily captured by a Boron atom.
The activated Boron atom quickly emits an alpha particle which causes ionization and a resultant current pulse.
40
8.4 PHOTOGRAPHIC DETECTION METHOD Photographic emulsions respond to radiation in much the same way that they respond to light. That is, radiation will darken a negative just as light will. In order to determine the radiction dose, the density or darkness of the negative is measuerd withia photo densitometer. With the proper filters placed in the film holder all types and energies of radiation can be detected.
4 8.5 THERMOLUMINESCENT DOSIMETERS Certain crystals, when exposed to radiation will have electrons knocked out of orbit. These electrons form a cloud inside the crystal and some of these electrons get captured in an imperfection called a trap. Heating the crystal at a later time releases the extra kinetic energy in the trapped electrons and, for certain traps, the excess energy is released as light, called thermoluminescence. This light that is picked up by a photomultiplier tube, amplified, and read out on a dial as total light or is plotted as a glow curve. The thermlouminescence is directly proportional to the radiation dose.
Thermoluminescent dosimeters can accurately measure radiation from 10 milli-roentgens to one million roentgens.
8.6 PERSONNEL MONITORING EQUIPMENT Personnel monitoring equipment includes Film BaGes, pocket dosimeters, and chirpers.
8.6.1 Film Badges As mentioned in paragraph 8.4, radiation will darken the negative just as light will. To determine an exposure the film is developed and the amount of light that it will transmit is measured with a densitometer. The less light that is transmitted the higher the dose. This is true for x rays, gamma rays, and beta radiation. Thermal neutrons do not darken the film directly, but are captured in a small sheet of cadmium that is surrounding the film. The cadmium is made radioactive and emits beta particles and gamma rays which darken the film. The process is different for f ast neutrons. A f ast neutron strikes a proton in the film and drives it out of the nucleus. The proton travels through the emulsion causing ionization.
When the film is developed this ionization appears as a track in the film. Thus a f ast neutron dose is determined by using a microscope to count the number of tracks in the film. The film badge is an individual's legal record of radiation exposure and should be worn on the upper lef t side of the body.
41
8.6.2 Pocket Dosimeters m
.11 A Pocket Dosimeter is a small ionization
/l
[i i
chamber Mgure 3-2) comprised of an electro-
[h j meter, a capi t.ttor, and a microscope. The elec-frI C trometer is a sr all stirrup that supports a move-ji b
able quartz fiber. The electrometer is attached to one end of a highly insulated capacitor. When the capacitor is charged, the quartz fiber is deflected a calibrated distance from the stirrup,
\\
igl g
due to their like charges. The quartz fiber can be P*
imaged on a calibrated reticule by looking through the microscope eyepiece. When radiation passes g
J through the dosimeter it causes ionization which 1I-rn neutralizes the charge on the electrometer, al-h lowing the quartz fiber to move toward the stir-S m
m
" w u rup.
The amount of radiation to which the DM dosimeter was exposed can be determined by j f; i
looking through the eyepiece and seeing how f ar J
L-the quartz fiber has moved across the calibrated DIRECT READING DOSIMETER reticule. If it is dropped, the hairline as seen on A e met,r.azng ces,-ev s a crec s ca irswment coa-ca-e, m u w ioaan,,o
>< eg e ae o 4r.oa
,a. 4...,-
a ma,
..im-...,
m,o m.ame n.
the reticule, wilI jurnp up scale and in many cases
- l*;;'
- l*L*;",' 3,; *",',",,Q.*;,5,'"f*;",f].
SC0ct 45p to read me 'ter -age om a reec'e (6) completely off scale. The dosimeter is used as a Tr n: e-.v e-ex a ~o retmen r>r o'.~cr
.s a me.eae, c aaz e ter waen ne cacar i : coa gec back up to the film badge.
"
- 7,'l7a's?'," ** "'S' "" "'"" "'"~ ' * *"
,8,
At 1*.
GOS rafter tS enoc 5.d to radah0*l,C"JESon Occurs,ft ne surrou d eg C*a* Der Ce: tas ng ?*e CParge a
T*. a..
8.6.3 Chirpers ce r..we,een - o<eoc%e m,m...oc.s.
e.c1,oa e, r
.,o.nei, ama 2 e.,
rec.,oe... o.
,at.e e, a uge,.ou,e.
~eog, s, oe,.C1.e.., m 10 a CahOra'ed r.1 C..
and t.ad *rougM a *"
1C0ct Chirpers are small battery operated Geiger a.o ne e' filw **at4*
Byl*.*
$ Ctf a ae3 ey 00 'Pf -
counters.
The output pulse from the detector 7,S,,";',,c2[,'O' '*. CCSCa:"',';,'l'g*lJ'lc;',",87;
- r. r.,~e..
charges a capacitor; when the voltage across the T*. ec,-.s in *a ov 3 temas om Co - ; s'
,rso:rea caa g es em on w e-cam s e; me ces*y-capacitor gets high enough, it triggers a neon tube
- SJ"37c" "',7 llW,o%,';C %3.}; [7,"S 7,'
3 y
T e
.,n,. ee.-er.,re,..
.-.sco, in.ee e a that drives a speaker and the result is an audible em4e ~. e
- on
" chirp."
The f aster this instrument chirps the INDIRECT READING DOSIMETER higher the radiation field. In very high radiation on,co,wra m.Bo,.go w,ei,* eeern Aa,no ce re u-.
- ao 9. vion re.ee.i cea.
Bilta Of a CaCaC?Or S
fields the individual chirps blena into a steady 0648 tion cmamcer 39d CParg'"9.u*.dC",n.
w.,..oc.,o m,ae.e,
,co.,r.
1s.n c the on cea-ter cec e* mg r C"Fye On ?*e C AL40;*0r tone that rises in pitch as the radiation level
- cre*c",n=o "r*e.. =.'~a a
^'"*-*"c"e""
mamma m g erry, increases. These instruments have been tested at Figure 8-2. Typical quartz fiber simetu more than 500 R/hr.
42
?^^
t z.
8.7 SURVEY INSTRUMENTS e
f T
g a
g 8.7.1 Geiger Counters Id 4$
\\
The Geiger Counter is a de-tection instrument that uses a halo-34
.(
gen gas quenched Geiger-Muller
[o g
\\
h tube to detect beta, gamma and
,5"
(
\\
\\~
x rays. This irutrument is not cali-
.., r */
-;j-m-$$
/
brated in Roentgens, it reads out the radiation detected in counts per Qg(g;h?ths^^ o>
w+
minute.
We have two models of y
Geiger Counters, one has three 1,!
y ranges and the other has four rang-
- r '
i 2
es. The operating ranges are: 0 to
/% g 500, O to 5,000, 0.o 50,000 and 0 to
,l ej i
500,000 cpm. There is ?lso a " test"
}
}
position to check the battery con-s}
dition.
f' w
4 The Geiger Counter is used to i[.
I g _4t-monitor or locate low level sources h47 e' s Q~ G.
of beta and gamma radiation and w
z- '
-y contamination (see Figure 3-3).
Operating Procedures Turn the switch to " B a t."
- f. -
anuu y
Turn the speaker (if used) to ON.
tu W.I L = w (
\\
c.uzz
- =
$}
Observe that the needle goes up into RO3834 tne green " Bat. OK" region. (If it coes not the catteries need to be Figt:re 8-3. The Geiger Counter replacea.) Turn the switen to the XI ranbe. If there is a cneck scurce attacheG to tne sice of the instrument, holc tne detector over the source to test tne meter. If tr.ere is no response the instrument will neec repair. Take the survey, sv.itcning ranges as neecec, and read the meter in counts per minute. Turn meter "CFF" wnen the survey is com pletec. An coject is consiGered radicactive or centcminatec if it reads greater tnan twice cacxgrounc or 200 counts per minute.
1here is mh/nr scale printec on some cI tne meters, uut tr.ese instruments are nct calioratec tes this scale.
al! of the Ceigcr Ccur.ters are calioratec so tnat 2,0(,0 cpm equals 1 rnK/nr.
43
8J.2 Juno Survey Meter The Juno is a monitorin6 nstrument that uses an ion cnamoer to measure dose i
rates from oeta, gamma and x rays. The cetecter uses air as tne counting gas and it is i
calibrated in Roentgens or milliroentgens per nour. We have two mocels of Junos: the Model 7 and the Model 8.
The Model 7 has three operating ranges: 0 to 50,0 to 500, and 0 to 5,000 mR/hr.
This instrument requires eignt catteries for operation. The Mocel S has five operating ranges: 0 to 5, 0 to 50, O to 500, O to 5,000 and 0 to 50,000 mR/hr. This instrument neecs only one 1.5 V "D cell" fc operation.
Botn mocels have an "ON" position that is used to warm up tne instrument, and a
" Set" position to set meter "zero." The Zero Set compensates for cecreasing battery voltage. There are two moveable slides on the cottom of eacn instrument: an acetate plastic sneet to shield out alpha particles anc an aluminum plate to shielo out tne beta particles (see Figure 8-4).
Operating Procedures:
1 Turn the instrument to "ON" and allow 15 to 30-second warm up. Turn switch to
" Set" and move neecle to "0" using the "Zero" knob. If the neecle will not come cown to "0" the battery (ies) are cead and will need to be replaced. After zeroing the meter, l
switch to XI or X10 scale and approacn the source of radiation slowly, cnanging ranges as needed to obtain the reading. Note range switch position anc needle reading to obtain the proper radiation dose rate. Open and close tne slice to differentiate between
~CC -
beta plus gamma and gamma only
-.m
/,
'M.
reading.
Turn meter "OFF" wnen survey is completeo.
i
}{'s
?
Jq 9
\\l t
~
F Figure 8-4. Juno Survey Meter 44
SJ.3 Victoreen 440 RF Survey Meter The 440 RF is a monitoring instrument that uses an icn cnanioer to measure cose rates from ceta, gamma, anc x rays. i-:ov ever, tnis meter is especially designec to measure low energy gamma anc x rays and to shield out all RF raciatien. These cnaracteristics make tnis an especially useful instrument arouno tne Linac.
Tne cetector uses air as the countin5 gas and tne instrument is calibratec in milliroentbens per heur. There are five operating ranges: 0 to 3, O to 10, O to 30, O to 100, and 0 to 300 mR/hr, anc a test position for battery cneck (see Figure.5-5).
Operating Procedures Turn range switch to " Bat." position, allow 30 seconds for warm-up. (If the needle does not come close to the black mark at the upper end of the scale, the batteries must be replaced.)
Switch to 300 range and allow needle to con.e down scale.
This O
instrument re-qaires a warm-up time of at
~
MdN:.
sw r.
pp least two min-aw
.,um.a utes on the 300 range.
Proceed 4
[' ;
to take the sur-
- vey, switching
- L.
"^
- J '
yty ranges as need-gg g 1
y
.+
xw ed. While taking Erhr W J 6; M f-the survey care-D
.h N
y$p.efqvw@Ef #I4 m y,p., JDa GC W,q a
fully note which a
.y iG M; y range you have u
, m.~ ~ 3 o(Br?'}
4.'-d selected and f
O read the appro-g priate scale.
[l l
Turn meter N
J k,
'., 9 "OFF" when sur-m T
vey is com-4%
?
pleted.
%m
,4
-w u q
%, M b
%g Figure 8-5. Victoreen 440 RF Survey Meter 45
~. -,,. -. -. - - -
8.7.4 Victoreen 392B This instrument is a monitoring instrument that uses an ion chamber to measure dose rates from gamma and X rays. This instrument was designed to be especially rugged for use in field radiography. There are three operating ranges from 0 to 10, O to 100, and 0 to 1,000 mR/hr; plus a ZERO SET position (see Figure S-6).
i Operating Procedure Turn the function switch to zero set and move indicator to "0" using the Zero Set Knob. If you cannot "0" the needle, one or more of the batteries are " dead." Most I
likely it is one or more of the 1.3 V mercury cells. (To change batteries, turn the two quick-connect screws on top of the case % to h turn, and separate the case-Leave the function switch in the Zero Set position and check the batteries with a voltmeter.
Replace the " dead" ones, put the case together and tighten the two quick connect I
l screws.) After zeroing the metec, switch to the proper scale and take the reading, which will be in mR/hr. Be sure to turn the instrument OFF to preserve the batteries.
l 46A pp 1
9
?
/ ?
\\
l hirke Q:%n=.y[, NN g
[
)
g r:k uu w
.~ e i
^
[
~,( _
S Np;;,-[%
- % ?.,,,.c 3
%;s
- pcq. :
n
%Yg,.
- .-'4 4
^4 -
4 f.s.
'L w~
. Q_
4.
m %, @: ??..ls;;%j
$ y w,;:,
. v, ;,
f Figure 8-6. Victorcen 592B i
46
8.7.5 The SNOOPY C
The Snoopy is a monitoring instrument A
that is used to measure neutron exposure rates Oh],
directly in Rem or millirem per hour.
The actual detector is a small BF filled propor-2 3
tional detector. The detector is surrounded by j
borated polyethylene that resembles the hu-man body in size and hydrogen content. The BF detector will only detect thermal neu-3 trons and the effect of the polyethylene is to
~
7 thermalize the neutrons.
The Snoopy will t-i e
detect neutrons of all energies from thermal g,4 to greater than 10 MeV. There are four op-
~
erating ranges: 0 to 2, O to 20, O to 200, and 0 to 2,000 mrem. A button on the instrument tests the battery condition (see Figure 8-7).
Operating Procedures Turn instrument on to any range, push t
7 "Batt. Chk." button and see that the needle goes upscale into the "Batt." region.
This '
[.} hk instrument has a slow time constant; there- -
,s;;
fore, the operator must be patient especially U A+;2ffhd h d i -
on the X1 arid X10 ranges and allow enough Ro3ss5 time for the meter to respond to the radiation, Figure 8-7. The Snoopy otherwise, an erroneously low reading will be obtained.
Turn the instrument "OFF" when the survey is completed.
L t+7
8.7.6 Alpha Survey Meters Two types of alpha monitors are used to locate and measure alpha radiation the Ludlum Model 12 and the Eberline PAC-ISA (see Figure S-8).
The Ludlum uses an air-proportional detector. It has four operating ranges: 0 to 500, O to 5,000 and 0 to 500,000 cpm, and a test position for battery check.
The Eberline PAC-ISA uses a scintillation detector (silver activated Zinc-Sulfide) to measure alpha radiation. It has four operating ranges: 0 to 2,000, O to 20,000, O to 200,000, and 2,000,000 cpm.
Both of these detectors have thin windows made of 1/2 mil aluminized mylar, so care must be used while surveying with these instroments. Do not set the detector-head down on an. -
g sharp or small enough to fit between the support grid. If you even touch the s indow on the Ludlum you will get a sudden burst of current and cause the needle to j ap. If you should punch a hole in the window on the PAC-1 AS, light will enter the detector chamber and give a high reading.
Operating Procedures for Ludlum i
[
Turn switch to " Bat." and see that the needle goes upscale
- ' %s. %._
yv to " Bat. O.K." area.
Switch to 7'0
, %y 4 the 0 to 5,000 range and hold
~.,,
detector against the check source N
on the side and see that the need-e ye., _
, WT '
le comes upscale. Switch to ap-
....._..:,~
propriate range and take survey.
i
I r
f s
meter % e.
Do not forget to turn
-3 "O FF."
\\ **
T
> f*i _
Operating Procedures for Eberline
%j
}
j' Turn switch to "Batt." and ;N '~-
'jj that needle moves up-observe scale to " Battery" position. Test
~
meter with check source if one is g-c s;
attached.
Take survey.
Turn f'r meter "OFF" when the survey is
~
T com pleted.
Figure 8-8. Alpha Survey Meters 1
48
8.8 MONITORING TECHNIQUES The monitoring techniques to be discussed include both detection operations and monitoring operations.
8.8.1 Detection Operations The purpose of the detection operation is to find sources of radiation.
The most sensitive survey meter, the Geiger counter, should be used to find Beta and Gamma emitters; the PAC-ISA should be used to fina Alpha emitters; and the Snoopy should be used to find neutron emitters.
Start the survey with the Geiger counter turning the instrument ON as described in the previous section. Turn on the speaker if one is provided because this simplifies the operation in that the operator can listen for the " clicks" rather than watch the meter. Remove the detector from the top of the meter and start the survey, cnanging scales as needed. Once the source of radiation is found the following course of action should be taken.
1.
If the nature of the source is not known, a Snoopy should be used to check for neutrons. The reason for this is that a number of neutron sources are used at IRT and these sources emit some gamma rays along with the neutrcas.
.However, the gamma dose may be only one tenth as strong as the neutron dose. If it is determined that the source is a neutron emitter, the procedure outlined under " Monitoring Operations" must be followed.
2.
If the source is a Beta or Gamma emitter and it reads less than 10,000 cpm (5 mR/hr), whatever action is necessary may be taken v.h as, removal to storage or applying the necessary shielding.
3.
If a Beta or Gamma source reads greater than 10,000 cpm (5 mR/hr), a monitoring instrument should be used to determine the dose rate and :he procedures outlined under " Monitoring Operations" must be follow 3d.
4.
If it is suspected that the source that was found with the Geiger counter is an Alpha emitter, it must be checked with the PAC-ISA. Alpha sources, like the neutrons sources, will also emit some level of gamma radiation. AtIRT the alpha sources are either sealed, covered with a thin coat of acrylic spray, or covered with a thin sheet of mylar. The only unsealed alpha emitters are some depleted Uraniam rods and blocks that are generally kept in plastic bags.
49
8.3.2 Monitoring Operations The purpose of monitoring operations is to determine the dose rate in mR/hr and to establish safe working limits for personnel exposure. The Junos, the Victoreens, and the Snoopie's are used for this operation.
Turn on the instrument as described in the previous section. Place the selector switch on the XI or X10 range and as you approach the source turn the selector switch up scale if necessary.
1.
If the source is a beam of radiation, stand to one side keeping your body out
~
of the beam while taking the survey.
2.
Take maximum advantage of any shielding available.
3.
If the source is out in the open hold the meter out in front of you as approved it; take the reading quickly and step back.
4.
If the radiation dose rate is 100 mR/hr or more the area is a "High Radiation Area" and if you remained in this area for one hour you would receive a full week's allowable radiation exposure. Therefore, if the radiation dose rate is 100 mR/hr or more call for assistance from Health Physics, the Radiation Safety Officer, or some other knowledgeable and qualified person.
5.
If the dose rate is less than 100 mR/hr take whatever action is necessary, working as quickly as possible, but in any case do not handle the source with your bare hands, use tongs, tweezers, or even pliers. Notify the Health Physicist or Radiation Safety Officer.
)
e SC 6
i
- 9. RADIATION PROTECTION 9.1 EXTERNAL RADIATION PROTECTION The primary considerations for radiation protection is to be aware that a hazard exis ts. Always be aware that the radioactive source is present whether shielded or unshielded.
How do you protect yourself from external radiation hazards? By using time, distance, and shielding.
These are the means available to protect yourself from external radiation exposure. That is, protection is provided by:
1.
Controllag the length of time you are exposed to a source of radiation.
2.
Controlling the distance between yourself and the source of radiation.
3.
Placing shielding material between yourself and the source of radiation.
9.1.1 Time The effect of time on your radiation exposure is quite straight forward. If you are in an area where the rad ation level is 100 mR per hour, in one hour you will receive 100 mR of exposure. If you stayed in the area for two hours, you wou.'d get 2 x 100, or 200 mR; if you stayed four hours, you would get 490 mR, and so on. Therefore, by limiting the amount of time you spend in a radiation area to as short as possible, you will help keep your radiation exposure to as low as practicable.
9.1.2 Distance The effect of distance on radiation exposure is not straight forward. But due to the effect of the Inverse Square Law, " distance" is an excellent means of protection.
The Inverse Square Law states: the intensity of radiation f alls off by the square of the distance from the source. See Figure 9-1 for a detailed explanation of the Inverse Square Law.
51
The formula for the inverse square law 9guIT is stated thusly:-
- jg[
UNIT AREA I
(d )2 I (d )2 1
2 2 2 s'
UNIT AREA r
I 1
- (d )2 g=
(d )2 RAD j
2 1/4 RAD
~
y y
UNIT AREA
, FT 1/9 RAD where:
N 3 FT I
= unkrown radiation intensity, RT-18175 g
Assume there is a source of radiation that I
= the known radiation intensity, measures x00 gammas per square foot at i ft 2
from the source. At 2 feet from the source the area has expanded to 4 square feet: with a total d
the measured distance for the
=
g of x00 gammas for the whole area, each unit area now only 900 gammas per square foot. At 3 unknownI,
g feet frora the source area has expanded to 9 square feet: with 3600 gammas for the whole the measured distance for the area, each unit area now has only 400 gammas per -
d
=
2 square foot. Theref ore, if a survey meter reads knownI,
i R/hr at I ft; the reading at 2 feet would be 250 2
mR/hr, and at 3 f eet it would be til mR/hr.
1 R/hr = 1000 mR/F r.
Figure 9-1. Inverse Square I,aw The formula wo*ks this way. A radiation source reads 1 R/hr at I ft. What does it read at 2 ft and 3 ft?
I
- ?, 12 = 1 R/hr, dy = 2 ft, d2
- I II g
1 R (1)2
_ igg) 250 mR/hr 2 ft 11*
=
=
(2) i I
I I I' = h = lli mR/hr 3 ft I g=
=
(3) l Simply stated the Inverse Square Law says this:
Every time you double the i
distance between yourself and a radiation source, you will decrease the dose rate by one fourth. Every time you reduce the distance between yourself and a radiation source by one-half, the dose rate will be four times higher.
i 52
This inverse Square law only works if the source is physically small in size or if you are f ar enough away from a large source. If you are close to a large source, such as a large snipping cask and the dose rate at I ft is 1 R/hr, it would probably be 500 mR/hr at 2 ft. In other words the dose rate only falls off as the distance increases, not the square of the distance, until you get 6 to 8 feet away.
9.1.3 Shielding Shielding is a much more complicated subject but it can be of great benefit to help reduce your radiation exposure.
Different types of shielding materials are used for the different types of radiation, in general alpha particles can be completely stopped by a sheet of paper or a thick pR.stic bag. Beta particles can be stopped by an eighth inch of aluminum or a quarter of an inc5 of plexiglas. Gamma rays can only be stopped by thick concrete shields, lead, or other dense materials.
Neutrons can be stopped by light weight materials containing a large number of hydrogen atoms mixed with certain materials that readily capture the neutrons.
9.1.3.1 Alpha Particle Shielding. Since alpha particles can be stopped by the outer layers of skin they are not generally an external radiation problem. However, if they get inside the body they can cause a great deal of damage because of the large amount of ionization that takes place in the surrounding cells. By keeping materials that emit alpha particles confined inside a container of some sort; such as a plastic bag, a cardboard box, or even an envelope there is generally no radiation hazard.
9.1.3.2 Beta Particle Shielding. Beta particles have a pretty good range in air; they can travel up to twenty f eet if they have enough energy. Most beta emitters that you will encounter, however, will only travel 6 to 10 feet in air. Beta particles can penetrate up to a half inch into the body and thus only cause a skin dose. A cuarter of an inch of plastic or an eighth of an inch of aluminum will stop most betas. Don't use heavy or dense materials for beta particle shielding. With dense shielding materials the beta particles are stopped or change direction suddenly due to the large negative charge created by all of the electrons that surround the heavy atom. When this happens, a gamma ray or bremsstrahlung is created; just like the effect we have at our Linear accelerator. So in this case the beta radiation hazard has been taken care of but a 53
gamma radiation hazard has been created. Therefore, for beta particle shielding use plastic or aluminum as thick as is necessary to reduce the hazard.
9.1.3.3 Gamma Ray Shielding (Not reacter or Linac). Gamma ray shielding can be very complicated because the ini.tial ge..ima rays generate secondary electrons which j
cause ionization creating other gamma rays of lower energies; also, high energy gamma l
rays can create positron-electron pairs which also create other gamma rays due to ionization and the annihilation of the positron. These secondary gammas are all of lower energies but they are still a hazard and must be taken into account when designing a shuld. We won't get into all of that, but just giue you a few basic f acts that will be sufficient to help you protect yourself. By the way, gamma rays can penetrate all the way through the body and cause just a few lonizations.
One of the first things you need to know is the term half-value layer. A half-i value layer is that thickness of material that will reduce the radiation dose to Y. of the original dose. For example: h inch of lead is a half-value layer for gamma rays of 60 1 MeV to greater than 5 MeV. If there is a Co source that reads 1 R/hr at I foot and we place a h inch sheet of lead 1 inch away from it, the dose rate at one foot will be reduced to 500 mR/hr; a second sheet of h inch lead will further reduce the dose rate to 250 mR/hr; a third sheet of lead will reduce it to 125 mR/hr; a fourth sheet.to 62.5 mR/hr; and so on.
So two inches of lead will reduce the original 1 R/hr to 62.5 mR/hr. Remember the term half-value layer, and remember that V2 inch of lead is j
a half-value layer for gamma rays. Good gamma ray shielding materials a:e heavy I
elements such as uranium, lead, iron, concrete, and earth. All of these materials can be mixed, or matched, or used alone as needed to provide the required shielding.
9.1.3.4 Neutron Shielding. Neutron shielding is even more complicated than gamma ray shielding because neutrons, after they have been slowed down, will almost always be captured by some atom, making that atom radioactive and thus creating other radiation hazards. So we must be very careful when selecting the materials that are to be used for neutron shielding.
A good neutron shield must contain a 'arge number of hydrogen atoms. Most neutrons are emitted at high energies and they need to stcike a number of atoms in order to Icse their energy and be captured. Since a hydrogen atom is only slightly larger than a neutrcn, the neutron looses much more energy striking a hydrogen atom 54
,~-
i i
i i
12 10 WATER 8
.c g
6 EGg 4
ALUMINUM CONCRETE
~
/
LEAD C
i i
t i
1 2
3 4
RT-20218 ENERGY IN MeV Figure 9-2. Half-value layers for different electromagnetic energies as related to thickness (inches) of iron and lead, aluminum, concrete and water than it does in striking a heavier atom. This bouncing around that the neutron goes through in order to lose energy is called "thermalization" and thermal or slow neutrons are much more readily captured or absorbed by an atom than f ast neutrons.
Certain elements such as boron, lithium, and gadolinum have several orders of magnitude greater probability of capturing thermal neutrons than do most other elements. This probability of capturing a neutron is called cross-section. Good neutron shields contain a large numoer of atoms of low atomic number for thermalization mixed with atoms that have a high thermal neutron cross section and emit few capture gamma rays.
Some good neutron shields are paraffin, paraffin mixed with boron, water, water mixed with boron, WEP (Water Extended Polyester), WEP mixed with boron or lithium, and just plain old concrete. Concrete is good because it also provides good gamma ray shielding. Roughly two inches of paraffin is equal to one half-value layer for neutrons from Cf-252. The human body is also a good neutron shield. The large amount of hydrogen in the body thermalizes the neutrons and then they are captured.
These three things that we have discussed, time, distance, and shielding, are the means by which you can protect yourself from External Radiation.
55
-. - ~ - -.
i a
4 i
The different kinds of external radiations can be ranked according to their degree of hazard. From the least to the most hazardous they are:
1.
Alpha 1
2.
Beta 4
j 3.
Gamma 4.
Neutron 9.2 INTERNAL RADIATION PROTECTION You can ingest radioactive materials by breathing them in, by taking them through your mouth, by cutting yourself with contaminated items, by getthg it into an open wound, and by abscrbing it through the skin.
How do you protect yourself from ingesting radioactive materials?
1 1.
Enclose the worker 2.
Enclose the work.
Along with this ' discussion of protection of the worker we will also discuss I
contamination control. Many facilities allow some degree of contamination in their work spaces and even office spaces.- But here at IRT our philosophy is, "if an area is contaminated to twice the natural background (which by the way is readily detatable),
you need to take protective measures."
4 i
i in order to prevent the spread of c6ntamination proper handling techniques must i
be employed. Gloves must be worn while working on contaminated equipment. While wearing gloves do not touch anything that must be kept clean. Do not answer the phone; don't handle pencil and paper to write notes; don't open a tool oox to get out a i
tool; and don't scratch your nose. Before starting work on any contaminated equipment, j
collect all of the tools you think you will need; lay them out on a clean cloth or paper towel and after you have used a certain tool put it into the contaminated tool pile.
When the job is finished any tools that you did not touch or use can be removed and put back where they belong. But check them first. The tools that you did use will nave to l
be decontaminated.
If you are going to work in a contaminated room you will need to wear shoe covers, protective lab coats, and gloves. When you leave the area first remove your lao coat. If the lab coat is highly contaminated unbutton it and pullit off gently turning it 4
3 56 f
inside out and put it into the radioactive trash. If the coat is not very contaminated i
take it off carefully and hang it up to be used again. Do not turn it inside out. Then remove your shoe covers. To do this, stand next to the control point line and pull off one shoe cover, gently; step over the line with that foot, and then pull off the second shoe cover and step over the line. At all times keep the foot wearing the shoe cover on the " Hot" side of the line and when pulling the shoe cover off, pull it toward the " Hot" area. In this way you don't get contamination falling onto the clean area. Finally remove your gloves by pulling them off and turning them inside out. Don't snap them when you take them olf because the contamination is liable to fall out all over the clean area. Check yourself with a G.M. survey meter and an Alpha survey meter if necessary.
l The procedures that have just been discussed are methods of enclosing the worker.
To endose the work or equipment, keep it in a glove box or hood and always transport it in a sealed plastic bag. If the contamination is all over a room, a control point is established at one door, all other doors and windows are kept closed. Everyone wears protective clothing while inside, and carefully removes it at the control point until the area is decontaminated.
How do you decontaminate something? Wash it with soap and water, wash it with alcohol, wash it with acetone, or use a contaminated vacuum cleaner equipped with an absolute filter. Don't use a brush or a broom because the radioactive materials will then get airborne and you will ingest them.
The methods of controlling contamination and the wearing of protective clothing that we have just discussed, are the means by which you can protect yourself from mgesting radioac:ive materials.
The different kinds of radiation can be ranked according to their degree of hazard when ingested into the body. From the least to the most hazardous they are:
1.
Gamma 2.
Neutron 3.
Beta 4.
Alpha.
57
_ _ _ _ = _
9.3 SAFETY AND HANDLING CONSID"_ RATIONS The IRT Radiation Safety Committee, which reviews all in. house programs utilizing radioactive materials, has established a set of general safety rules for handling uncontained radioistopes.
1.
If at all feasible, operations should be carried out within the confines of a hood or glove box, even if the quantities are sufficiently small to warrant open bench top operations.
2.
All operations involving finely divided particles of pyrophoric radionuclides must be carried out under an inert atmospherr. within a glove box. Storage of these materials must be in fireproof containers.
3.
Keep work area free of all unnecessary equipment and cover work area with protective absorbent paper. If possible, carry out operations within con-tainers or catch trays and keep tools, equipment, etc., in localized area within suitable containers.
4.
Plan operations to minimize handling and transfer of materials and amount of material used.
5.
Keep waste generation to a minimum and r.aintain radioactive waste -
containers in i 1 mediate area; do not place radioactive waste in ordinary trash. Keep SNM and by-product wastes segregated. Contact Health Physics f or specific instructions for disposition.
l 6.
Use protecive clothing as necessary and monitor self prior to leaving work area.
7.
Do not handle loose material directly; use tongs, tweezers, pipettes, etc. Do ny use mouth technique for pipetting operations.
8.
Make routine contamination surveys daily until operational techniques are perf ected and then if warranted on a weekly basis. Send wipe samples to Health Physics for analysis.
9.
Use portable air sampler in vicinity of operations whenever operations are in progress. - Send samples to Health Physics on a daily basis 4
for analysis.
58
i 10.
Store materials when not in immediate use in hood and return to Health Physics for storage when operations are completed. Store materials in closed -
metals cans and, if liquids, include enougt
- r. arbent material in container, to fully absorb all material.
1
]
11.
In case of spills or any unusual events, contact Health Physicist or Radiation Saf ety Officer for assistance'.
12.
Do not flush radioactive liquids down the drain. Contact Health Physics for j
specific instructions for disposition.
i 4
I I
i t
d 1
59
Me intentionally left blank) i
(
t f
)
f l
l 60
=
- 10. RULES AND REGULATIONS The rules and regulations that cover the use of Radioactive Materials are: The United States Nuclear Regulatory Commission Rules and Regulations, Title 10 - Chap-ter 1, Code of Federa! Regulations; and California ~ Radiation Control Regulations, Title 17, California Administrative Code, Chapter 5, Subchapter 4.
The names of these rules and regulations are generally shortened to: NRC-10CFR and CAC-Title 17. The specific sections of these regulations that concern you are:
10 CFR 19,10 CFT 20, and Title 17 Group 3.
Actually the California Code in most cases just repeats the Federal Code, so we will concentrate on the Federal Code.
Other documents govern our use of Radioactive Materials and they are:
1.
State of California, Department of Health, Radioactive Material License No. 2463-80 2.
U.S.
Nuclear Regulatory Commission Materials License No.
04-18479-02(DNL);
3.
U.S. Nuclear Regulatory
- Commission Materials License 'No. 04-18497-03 (AIDECS);
4.
U.S. Nuclear Regulatory Commission, Special Nuclear Material License No. SNM-1405; 5.
IRT Corporation, Radiation Work Authorizations; The final set of regulations that cover our use of radioactive materials are:
6.
The United States Department of Transportation Rules and Regulations, Title 49, Code of Federal Regulations," Transportation."
61
10.1 TITLE 10 CFR 19. " Notices, Instructions, and Report to Workers: Inspections."
This part of the regulation covers the employers responsibility to the worker.
Briefly this part states:
1.
Certain documents: namely,10 CFR 19,10 CFR 20, and our Radioactive Materials License must be posted or otherwise made available to the employees.
2.
The employer must instruct the worker in Radiation Safety and rules and regulations.
3.
An employer must furnish any worker a copy of his radiation exposure, in writing if the worker so requests.
4.
A worker or the workers representative may accompany a Commission inspector while he inspects the f acility.
5.
The Commission inspector may consult privately witn the workers.
6.
Workers may request the Commission to inspect the facility.
7.
Employer may not discriminate against an employee who exercises his rights under this regulation.
10.2 TITLE 10 CFR 20. " Standards for Protection Against Radiation."
This part of the regulation is much longer than part 19 but it contains much information that would be beneficial for you to know. Some of the more important provisions are given below.
10.2.1 Exposure Limits Occupational exposure limits apply to persons over 18 years of age who are exposed to ionizing radiations as a result of their employment. The occupational i
exposure limits below are applicable to all persons for whom IRT has control l
responsibility.
62
Calendar Annual Quarter Accumulated (Rem)
(Rem)
Whole Body, Gonads 5(N-IS) Rem
- 5 1.25++
Bloodforming Organs, Lenses of the Eyes Specific Organ other 15 5
than those listed (e.g.,
Lung, GI Tract)
Bone, Thyroid, Skin of 30 7.5 the whole body Hands, forearms, feet, 75 18.75 and ankles Where N is the age in years, and is greater than 18.
++An individual 18 years of age or older may receive an occupational dose to the whole body greater than that permitted above provided that: (1) during any calendar quarter the whole-body occupational dose shall not exceed 3 Rem; (2) the user has made a prior determination of the individual's accumulated whole-body occupational dose; and (3) the dose to the whole body added to the previously accumulated whole-body occupational dose shall not exceed 5(N-18) Rem, where N equals the individual's age in years at his last birthday.
The value 5 R/yr is based on criterion that a person receiving this dose beginning at age 18 and extending through his working life will suffer no observable ill effects.
No individual under 18 years of age may receive an occupational dose in excess of 10 percent of the limits specified above. Pregnant women shall not be occupationally exposed at any time during their pregnancy. Exposure limits and policies contained in this regulation are based on the recommendations of the National Council on Radiation Protection and Measurements (NCRP), the Federal Radiation Council (FRC), and the.
International Commission on Radiological Protection (ICRP).
i 10.2.2 Personnel Monitoring Each user shall supply appropriate personnel monitoring equipment to, and shall require the use of such equipment by:
1.
Each individual,18 years of age or over, who enters a controlled area under such circumstances that he is likely to receive ir. any calendar quarter a dose 63
exceeding 300 millirem to the whole body; or 5 rems to :he hands and forearms, or f eet and
.L.les; or 2 rems to the skin of the whole body.
2.
Each individual under 18 years of age who enters a controlled area under such circumstances t
he is likely to receive in any calendar quarter a dose exceeding 60 mulirems to the whole body; or 900 millirems to the hands and forearms, or feet and ankles; or 400 millirems to the skin of the whole body.
3.
Each individual who enters a high radiation area.
10.2.3 Signs a.
Radioactive Materials The radiation symbol must be included on all radiation warning signs. The symbol is the conventional three bladed design, with the blades being colored magenta or purple on a yellow background. The "Cau-tion Radioactive Material" sign or label plus symbol (Figure 10.1) shall be posted in areas where certain m2m68 amounts of radioactive materials are used.
Each container or device in which is transported, Figure 10-1. The radiation stored, or used certain quantities of radioactive mate-8Y" I
rials must have affixed a label bearing the radiation symbol and the words " Caution Radioactive Material." Labels shall also state the quantity ar.d type of radioactive i
material and the date of measurement.
b.
Radiation Area Each area in which there exists radiation at such levels that an individual could receive in one hour a whole body dose in excess of 5 millirem, or in any five consecutive
~
cays a dose in excess of 100 millirem must be posted with a sign bearing the radiation symbol and the words " Caution Radiation Area."
c.
High Radiation Area Each area in which there exists radiation at such levels that an individual could receive in any one hour a dose at the whole body in excess of 100 millirem, must be posted with a sign bearing the radiation symbol and the words " Caution High Radiation A rea."
64
d.
Special Requirements for High Radiation Areas Each entrance or access point must be:
1.
Equipped with a control device that will automatically reduce the radiation level to less than 100 mR/hr upon entry into the area, or 2.
Equipped with a visible or audible alarm to alert the individual entering the area and a responsible second party that an entry is being made, or 3.
Maintained locked except when access is required, with positive control over each entry.
4.
These controls must be established in such a way that no one is prevented frorn leaving a High Radiation Area.
5.
If the High Radiation Area will exist for only 30 days or less, direct surveillance may be substituted for other controls.
6.
Alternative methods of control may be"used if approvalis first received from the applicable regula' ory group.
t Each radiation machine which is capable of producing, in an accessible area, a dose rate in excess of 100 mR/hr shall be equipped with a visible or audible alarm to warn any individual at or approaching the tube head or radiation port that the machine is producing radiation. The alarm shall be activated automatically only when radiation is being produced.
10.2.4 Receipt of Radioactive Material There are special procedures that must be followed for picking up, receiving, and opening packages of radioactive materials. Therefore the RSO or HP must be notified upon receipt of a package of radioactive material so that the proper procedures are followed.
10.2.3 Incidents Certain incidents must be reported to the proper state or federal authority.
These incidents include:
1.
Thef t or loss of radioactive material.
2.
Personnel exposure greater than 5 Rems to the whole body.
65
3.
The release of radioactive material to the environment.
4.
A loss of one day or more of the operation of any facility.
5.
Damage to property in excess of $2,000.
~
Depending upon the severity of the incident, the reports must be made immedi-ately, within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, or within 30 days. Therefore the RSO and the HP must be notified immediately for assessment of the incident so that the timely notifice. tion can be made and submitted to the proper authorities.
10.3 LICENSE REQUIREMENTS California Administrative Code Title 17 Chapter 5, Subchapter 5, Group 3 is the nomenclature for the California Radiation Control Regulations. These regulations are similar to the federal regulations except that they go into more detail. With California being an " Agreement State," enforcement of radiation control regulations is the state's responsibility, so we have to follow these rules.
IRT Corporation has been issued four licenses to handle radioactive materials.
One license was issued by the State of California and the others were issued by the U.S.
Nuclear Regulatory Commission. Our State of California licenses is No. 2468-80. This license specifies the types and quantities of radioactive material we may possess, and where and how we may use it. This license covers all radiation producing machines and radioactive materials except U233, U235, and Pu. The three licenses from the NRC cover IRT's use of Special Nuclear Materials, Delayed Neutron Logging, and AIDECS Operation.
These licenses require IRT to establish a radiation safety organizaion consisting of a Radiation Safety Office (RSO), the Radiation Safety Committee (RSC), the Criti-cality Safety Committee (CSC), and the Health Physics staff. The RSC is composed of five members, including the RSO.
It represents both management f unctions and operating functions.
The purpose of the radiation safety organization is to assure compliance with all license requirements and compliance with established radiological safety standards, to administer SNM safeguards and accountability, and to provide license administration.
66
10.3.1 The Radiation Safety Committee (RSC)
The RSC acts in both a review f unction and an audit f unction. It is responsible for the critical review of all radiation related work within the company and must give authorization for such activities in the form of a Radiation Work Authorization.
10.3.2 The Criticality Safety Committee (CSC)
The CSC performs both a review function and an audit f unction in giving approval for, and inspecting only those operations involving the use of SNM.
10.3.3 The Radiation Safety Officer (RSO)
The. RSO initially reviews all RWA's to establish that all personnel on the RWA are authorized to perform the work; that equipment, facilities, and procedures are adequate for the job; and that all license requirements are satisfied. He must review and inspect all operations using radioactive materials. It is the RSO's responsibility to approve all purchases of radioactive sources and all shipments of SNM.
10.3.4 The Health Physicist (HP)
The HP provides various services such us personnel monitoring, dose rate measurement, radioactive material detection and assay, air and water sampling, environmental mcidtormg, and instructional and training programs. He is to inspect all radiation operations and to terminate any experiment that is violating the regulations or special requirements, or that is unsafe.
67
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- 11. THli LINEAR ELECTRON ACCELERATOR The Linear Electron Accelerator, Linac for short, is a device that accelerates electrons to very high speeds. When ions or subatomic particles are accelerated to high speeds they experience an increase in their energy levels and these highly energetic particles can be made to do useful work. The major projects that are conducted at the IRT Linac are: sterilization of Medical products, electron implanation and enhancement of diode materials, cross linking of plastics, radiation enhancement of certain mate-rials, and the use of the electrons as a large burst source of radiation for testing electronics components.
There are two accelerators at the Linac. Both have just one accelerator section.
The electrons are accelerated by RF energy (High Frequency radio waves) through a pipe which is under vacuum. Powerful magnets are used to keep he electrons tightly bundled together in the center of the pipe and to steer them to the selected output port.
A map of the Linac facility is shown in Figure 11-1.
There is one thought to keep uppermost in your mind while at the Linac.
These machines can be lethal Both machines can produce radiation doses higher than 100,000 R/s in the beam, if you were in the cell with the machine on, you could receive a lethal dose of radiation in just a few seconds even if you were not in the direct beam. However, you can easily protect yourself by simply following the Linac Safety Rules.
No one has ever been irradiated by the IRT Linacs; in fact, only one person has ever had.a close call, and that was because he ignored the safety rules.
69
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11.1 FUNDAMENTAL LINAC RADIOLOGICAL SAFETY RULES PROTECT YOURSELF AND OTHERS AT THE LINEAR ACCELERATOR THE MACHINE CAN BE LETHAL 1.
Safety Plugs. Everyone entering the accelerator experimental rooms must take a safety plug and wear it en his external clothing. This plug interlocks the Linac and it cannot be started until all plugs are returned to the board.
The plug is your personal Life Insurance.
2.
Chirpers.
If there has been a high power run, everyone entering the accelerator experimental areas must also take a chirper. Test it before you enter the area. This pocket geiger counter will warn you of any excessive i
radiation fields.
3.
Film Badge and Dosime:er. Everyone at Linac must wear both a film badge and a pocket dosimeter. It must be worn in plain view at all times. The should be worn in the vicinity of the lef t breast pocket. Read your dosimeter every morning. Check it again every night and more of ten if necessary. Do not let it go over 100 Rem without notifying Health Physics.
4.
Safety Switches.
Red scram buttons and emergency safety switches are located in many areas at Linac. Learn where the ones in your area are and if necessary USE THEM.
5.
Criticality Alarm. The criticality alarm is the KLAXON horn. If you hear the klaxon, get out as f ast as you can and to do the evacuation control point.
Control points are at Guard Station 2 or the Linac Annex Parking Lot.
Health Physics must give clearance for re-entry.
6.
Responsibility. The Linac operator and the experimenter are responsible for the safety of all personnel during Linac operations.
7.
Closing the Cell Shield Doors.
Before closing a shield door to resume operations of the Linac, the operator must:
a.
Inspect all areas and be sure that everyone is out of the cells; b.
Blink the lights in the cells; c.
Make sure that the horn sounds as the cell door is closing.
71
If you are inside when the horn sounds, hit the nearest scram button and open the door from the inside.
8.
Monitoring the Entry. If there has been a high power run use a JUNO survey
' meter (window open) to evaluate radiation hazards whenever entering the accelerator or experimental areas. Stay.out of areas over 100 mR/hr unless it is specifically approved by the Health Physicist.
9.
Radioactive Material.
The Health Physicist must approve bringing any radioactive material into the Linac f acility. Everything being removed from the cells must be checked by the Health Physicist. Clean items will be marked with CLEAN stickers and can be removed.
Contaminated or radicactive materials must. be marked -appropriately and.a Radioactive Materials Removal Record must be completed by Health Physics.
10.
Health Physics Services.
Health Physics services are normally available 8 AM to 5 PM Monday through Friday..Outside this. time call Paul R.
Maschka 746-5487 or Kay L. Crosbie 276-3741.
4 72 i
1 m
-m
m.
- 12. CALIFORNIUM-232 Californium-252 is element number 98. It does not exist in nature; it is manmade.
Most Cf-232 made in this country is produced in the ORNL High Flux Isotope Reactor.
242 241 The target material for production of Cf-252 is Pu or Am. In order to obtain Cf-242 252 from Pu 10 neutrons need to be added to the nucleus which also must undergc 241 four beta decays (see Figure 12-1); from Am 11 neutrons need to be added and there has to be three beta decays.
FISSION FISSION Cf Cf250
- Cf251 --= C f '
249
\\
\\
290d 3.1 h 249 250 Bk
-=- Bk N
FISSION
/
\\
Cm
-- C m
- Cm
-+ Cm247 =- Cm248 249 244 245 246
--= C m N
N N
26 min.
2.0 h 25 min.
\\
\\
\\
243 244 245 246 Am
--.- A m
--. Am
-- Am N
N N
5.0 h it h it d N
N N
Pu242
,py243 _,,py244 --- P u245
,py246 Figure 12-1. Production of Cf-252 from Pu-242 Cf-232 decays by alpha emission and by spontaneous fission. Spontaneous fission is the property of Cf-252 that is useful because three or four neutrons are released in the process. We use these neutrons in various ways, such as, neutron radiography, gauging of low density or hydrogenous materials, testing reactor fuel rods, and activation analysis.
The radiations frota Cf-252 are alpha particles, neutrons and gamma rays. The neutron dose rate is 13 times higher than the gamma dose rate with one mg of Cf-252 73
producing a radiation dose of 2200 mrem /hr neutron and 160 mR/hr gamma at one meter in air. The alpha particles emitted by the Cf-252 cannot be detected from the IRT sources because these sources are double encapsulated.
Unlike most other radioactive materials, the amount of Cf-252 contained in a source is expressed in weight figures,~ micrograms (pg) or milligrams (mg), rather than the normal disintegra-tion figures, millicurie (mci) or Curie (Ci). However,1 mg of Cf-252 contains 536 mci of radioactive material.
The methods to use to protect yourself while working around Cf-252, in order of importance, are:
l 1.
Rehearse the procedure to find problems areas 4
i 2.
Limit your time to as short as possible (work quickly) 3.
Stay as far away as you can 4.
Use as much shielding as possible.
r i
4 4
l l
74
- 13. RULES FOR SAFETY The primary objective of radiological safety is to keep all personnel exposures as f ar below the permissible limits as is practicable. In order to achieve this objective, certain rules have been set up to guide the worker in handling radioactive materials and while working around radiation-producing machines at IRT.
l 1.
Prior to beginning work with radioactive materials or radiation sources, each employee shall be informed by his supervisor of the practices and procedures applicable to his work location or assignment. The Health Physicist shall discuss the radiations and contaminants he may encounter, his responsibilities for radiation protection, and the monitoring devices and protective equip-ment provided for use in radiation exposure measurement and control.
2.
Radioactive materials and radiation sources shall be conspicuously marked at all times. The marking shall bear the magenta radiation symbol, the words
" Caution, Radioactive Material," identification of the radioactive substance, and an indication of the amount of radioactivity.
3.
All sources shall be confined to work areas that are properly posted.
4.
When a source is received from another user, the receiver should check the source level aside from any labels or radiation levels provided by others.
5.
Radioactive sources exceeding 0.5 pCi should not be handled with the fingers.
Forceps or tongs of suitable length should be used.
6.
Use a catch pan of nonbreakable material under any vessel or equipment that may leak or spill a radioactive liquid.
7.
Protect personnel in adjoining areas from exposure due to your use of radioactive materials or radiation-producing machines.
8.
Return radioactive material and radiation sources to proper storage when not in use. Radioactive materials must not be stored in offices.
75
9.
Do not track contamination away from the scene of the spill. If a spill occurs, hold your breath and leave the area, closing doors and vents as much as possible; stay near the area and summon help; prevent others from in-advertently entering the area.
10.
Personnel-monitoring instruments of appropriate type and sensitivity must be worn by each individual working within a zone of radiation exceeding 2 mrem /hr.
11.
Protective clothing, such as coats, coveralls, shoe covers, caps, gloves, etc.,
shall be worn by each person as necessary to prevent contamination of bis body.
12.
Contaminated garments shall not be worn away from the scene of the contaminating work.
13.
Upon leaving the work area, each person must monitor his face, hands, hair, and clothes for contamination using a suitable survey instrument.
14.
All equipment must be checked for radioactive contamination prior to removal from a contamination control zone.
15.
Smoking, eating, and drinking are not permitted in laboratories or work rooms in which unsealed radioactive materials are used or stored.
16.
Pipetting of radioactive solutions by mouth is absolutely forbidden.
17.
Personal effects should not be stored in contamination control zones.
1 18.
Radioactive materials must not be discharged into the sewer or deposited in ordinary trash baskets.
19.
Food shall not be stored in refrigerators or other containers which are used f or storing radioactive materials.
20.
Do not mix contaminated tools or equipment with uncontaminated items.
21.
If adjustment or repair of personnel-monitoring equipment and Health Physics survey equipment is required, the equipment should be Serviced by HPS.
22.
Dispose of radioactive waste in properly marked waste containers.
23.
Do not place nonradioactive waste in radioactive waste containers, t
24.
Carefully plan and rehearse all operations involving the use of radioactive materials.
76
- 14. RADIATION WORK AUTHORIZATION The Radiation Work Authorization (RWA) is usec; to describe all operations involving radioactive materials. The RWA is submitted to the Health Physicist who reviews it for: completeness and obvious errors or omissions. The RWA then goes to the Radiation Safety Officer who reviews it and makes recommedations for approval or relection by the Radiation Safety Committee. The RSC reviews the operation in detail and makes recommendations cr comments which become part of the RWA.
It is imperature that RWAs be submitted early in the planning stage for the operaticas, so that the RSC may pass on the adequacy of the equipment, shielding, and operational procedures; and make any other comments t' hey deem necessary.
14.1 PROCEDURES FOR INITIATING AN RWA The RWA, shown in Figure 14-1 is separated in a number of sections. The information required f or each Block is described below.
Block 1:
Self-explanatory. The RWA No. will be assigned by the RSO.
Block 2:
Name the people who will assume these duties.
Block 3:
Indicate the room, building, or specific area where the work will be done.
Block 4:
Describe the program including: program name and purpose, proce-dures that will be followed, drawings of the equipment and shielding; and emergency procedures.
Block 5:
Indicate the amount and physical description ci each radioactive isotope.
Block 6:
If the operatic,n involves unsealed radioactive materials that could become airborne indicate the isotope, possible amount, and physical form.
.77'
l IRT Corporation RADIATION WORK AUTHORIZATION NO.
1.
( ) New Request Date Submitted
( ) Renewal of RWA No.
Date Required 2.
Principal Investigator:
)
Material Custodian Alternate 3.
Work location
.=
4.
Description of program (include methods, sketch of the apparatus and setup showing the shielding provided). Attach supplements referenced to this request,if necessary.
S.
Quantities of Radioactive Material involved in this operation:
Isotope Amount Material Description (Physical Form) 6.
If Airborne Radioactivity is created indicate major Isotopes, quantity and physical form.
Isotope Amount Gaseous or Particulate NONE 7.
Will a contamination control bo.mdary be needed:
( ) Yes
( ) No if yes, describe. Attach supplements referenced to this request,if necessary.
E A2 Figure 14-1. Radiation Work Authorization I
(Sheet 1 of 2) 78
8.
Is Special Nuclear Material to be used under this RWA 7
( ) Yes
( ) No If Yes, specify use and storage locations.
Total throughput of special nuclear material during one-year periods
(
)
grams U-235; (
) grams plutonium;
(
) grams U-233 g Form in which material will be returned to accountability 9 Upon receipt of the radioac+ive material to be utilized as described herein, (1) (We) shall be re-sponsible to maintain the exposure of any individual to the radiation therefrom to as low as prac-ticable limits. 0) (we) have read, are familiar with, ar.d will comply with Title 10; Part 20 Code of Federal Regulat2ons (Standards for Protection Against Radiation), and Title 17, Chapter 3, Sub-chapter 4. Group 3, California Administrative Cc;* (Standard for Protection Against Radiation),
IRT Radiological Safety Guide, Gf applicable) the Linac Radiological Safety Regulations, and comments under Section 11. 0) (We) have successfully passed the Radic!ogical Oafety Test:
Princ2pai investigator Maternal Custodian Alternate Matertai Custocian ADDITIONAL AUTHORIZED PERSONNEL 10.
Take to H.P. for discussion and approval.
11.
Radiation Safety Committee Comments:
12.
Approvals:
Cognizant Manager:
Date Health Physicist:
Date Radiation Safety Officer:
Date Chairman, Criticality Safety Committee:
Date Chairman, Radiation Safety Committee:
Date This Approval Expires on:
Frequency of auditing 13.
Have authorized personnel read and sign above. Return to Radiation Safety Officer.
=
T t
Figure 14-1. Radiation Work Authorization Gheet 2 of 2) 79
~
Block 7:
If the operation involves unsealed radioactive materials describe the methods that wdl be employed to prevent the spread of radioactive
~!
contamination.
233U, 235U and Plutonium. -
Block S:
For Special Nuclear Materials, i.e.:
Provide the required information.
Block 9:
Read the statement of responsibility and supply the names of the people involved incluaing the additional authorized personnel. "Au-theri' d Personnel" does not necessarily mecn capable and compe-tent to handle any or all radioactive materials. It merely means that these persons are authorized to be named on an RWA and either have passed a training course or have been granted a waiver.
Block 10:
Self explanatory.
Block 11:
RSC comments, requirements and suggestions.
Block 12:
Approvals Block 13:
Procedure for the P.I. to follow after the RWA is approved.
l 30
_. - _. _ _ _ _,, - _ _. ~ -,,
- 15. SHIPMENT OF RADIOACTIVE MATERL'LS The rules and regulations govern.ing the snipment of radioactive materials are administered by the U.S. Department of Transportation. The rules are contained in Title 49 CFR " Shipment of Hazardous Materials." The specific section that contains most of the radioactive materials regulations is Title 49 CFR Part 173.
These regulations are quite complicated and they spell out special re uirements and forms which must be completed prior to the shipment. Because of these special requirements, the RSO or HP must be contacted well in advance of the shipping date, so that proper shipping containers may be obtained and all the necessary paperworks completed.
15.1 SHIPMENTS BETWEEN IRT'S SAN DIEGO FACILITIES All shipments of radioactive materials between the Linac, 7650 Convoy Court, 7070 Convoy Court and any future IRT Facility must be accompanied by a completed Radioactive Material Removal Record, Form !F-72-1 (See Figure 15-1).
Exempt packages and packages bearing the Radioactive I label may be transported in the trunks of personal vehicles. Packages bearing the Radioactive II label must be transported in an IRT vehicle. Packages bearing the Radioactive Ill label must be transported in an IRT vehicle to which " RADIOACTIVE" placards have been applied on all four sides.
15.2 SHIPMENTS TO OTHER COMPANIES All shipments of radioactive materials to other companies or to IRT facilities outside of San Diego must be accompanied by a completed Radioactive Material Shipping Record Form IF-163-2 (see Figure 15-2). All items of data on this form are required by D.O.T. 49 CFR.
The person requesting the shipment must provide the name, address, and license number to the RSO or HP. No radioactive materials may be shipped to any Company, person, or governmental agency until confirmation has been received that they have a valid radioactive materials license that allows them to possess the material, and a copy of the applicable sections of their license has been received or is being sent.
81
01064 RADICACTIVE MATERIAL REMOVAL RECCRD Shipped to O
Recoved by Q
Address Recipiant's A.E.C. or State License No.
l City State Material Shipped or ?emoved (Description)
~
isotooe(s)
Estimated Activity Physical Form Shicoed via Gas Liquid Solid D
O Transport Group DOT Duantity SNM Weight (gms)
Fissile Class HEALTH PHYSIC $ MONITORING RESULTS Material Shipping Container External Surface Surface Radiation One Foot One Meter From Surface From Surface Surface Alpha Alpha i
Contamina-tion Beta-Gama Be ta-Gama Labels Ret. sired Transpcrt index j
SPECI AL INSTRUCTIONS FCR OPCPING THE PACKAGE:
)
i 1
l CEstiricATicg This Is to certlfy that the articles described above are property classified, marked packaged. aad o
labeled according to the regulations of the Cesartment of Transportation and the Atomic Eaergy Co-mission.
Health Physics Date tuSTOMER RL=CVAL: The undersigned acknowledges receipt of this Radioactive "aterial aad certifies that be is author f red to receive the material under authority of Radioactive Paterials License %.
Signature a te IF-72-1 wMtTE - ALE Y ELLQ w - S HIPPING / CUSTQ wtR Figure 15-1. itadioactive Material Removal Record 82
RADIOACTIVE MATERIAL iar SHIPPING RECORD E WFJE
-.,e No.
- 1. TO:
ATTN:
=
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a. ~ u.Ca assO see Consstiassca eitu apetCaeLi efGuLarcset e ussotagfa8@ theaf 27 Componafsons DOES esof Guamantry sustrTT OF 90f08C CONfter? OP test anatt.aL. ce eseg aCCLeaCV 08 fisE DE5Caefces asso 7anat et Dof t esO7 er a=* eov massammt ftse attusEtt Op f'ing naaften p(e Tseg pr.Anpogg som eneCas av asev aseo ama CLaese or eccete.S *? COA 80matcss eTS OptiCESS assants am0 tes*LCvtfS 8eces anO esLL seOLD rensas esama4Est acan 769 Lesogassapeti agtsaSE Juev secassf18 Ossgase en ota a8 to peopfe'v Ce s amesnuG Ot/T o8 Ce masuLieue Pulces inst RacconC7mL 'OssC os rse on Lossthe C# ' p=eo*pt#743 op vtag asaft.om Longop yet os peorgery T*44 seMAssoous at en mte.
uC.
e a
=
e_.
.~e.--
=
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s,
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e Figure 15-2. Radioactive Material Shipping Record 83
15.3 SHIPMENT BY AIR Radioactive materiais may only be carried on " Cargo Only" aircraf t except for certain Medical and R and D materials and specified " Limited Quantity" radioactive materials that meet the " Exempt" requirements. Three different forms must be made out and the package must be marked properly for air shipment. If even one mistake is made on any of the four items, the package and all paperwork is returned to the shipper for correction. It is much easier to ship radioactive materials by ground transport than by air.
15.4 SHIPMENT OF SPECIAL NUCLEAR MATERIALS All shipments of Special Nuclear Material, even those going to other IRT facilities must be approved by the RSO. Prior to the shipment of any SNM, a number of different form for the NRC, snipper, and receiver must be completed; the receiver must be notified of the shipment and must confirm possession of a valid license; and either the shipper or receiver must take responsibility for safeguarding the material during transit.
l i
l i
l l
I 84 i
- 16. DEFINITIONS Activation: The process of inducing radioactivity by irradiation.
Airborne radioactive material: Any radioactive material dispersed in the air in the form of dusts, fumes, mists, vapors, or gases.
Aloha partide: A helium nucleus, consisting of two protons and two neutrons, with a double positive charge. A stongly ionizing and weakly penetrating radiation.
Beta particle: A charged particle emitted from the nucleus of an atom and having a mass and charge equal in magnitude to those of the electron. More penetrating but less ionizing than an alpha particle.
Contamination: An impurity which pollutes, coats, or adulterates anotner substance. In radiological safety, contamination refers to the radioactive materials which are the sources of ionizing radiation.
In most cases this contamination is radioactive dust covering an object or suspended in a liquid.
Curie: The basic unit of radioactivity. One curie (Ci) is the activity corresponding to a disintegration rate of 3.7 x 10' disintegrations per second.
Dose: The quantity of radiation absorbed per unit of mass, by the body or by any portion of the body.
Dose rate: Radiation dose delivered per unit time.
Fissile materials: Uranium-233, uranium 235, and plutonium-239.
Gamma and x-radiation: Electromagnetic photons with wavelengths less than ultra-violet, traveling with the speed of light, and each conveying energy proportional to its frequency.
High-radiation area: Any area, accessible to personnel, in which there exists radiation at such levels that a major portion of the body could receive in one hour a dose in excess of 100 mrems.
LINAC: Linear Accelerator. A device that accelerates electrons or other particles to high speeds. The acceleration is done along a straight line.
Maximum permissible exposure (MPE): The greatest whole-Lody radiation dose per-mitted an individual in a given circumstance.
85
Neutron radiation: A neutron is a chargeless particle with a mass similar to that of the proton. Fast neutrons convey energy from their source by virtue of the velocity at which they travel. Slow neutrons may be termed thermal neutrons when their kinetic energy is equivalent to that of the motion of the atoms which surround them. Thermal neutrons do not convey significant energy from their origin but are capable of releasing energy when they are captured by an atom making it radioactive.
Occupational dose: The dose received by an indiviaual: (1) in a controlled area, or (2) in the course of employment, education, training, or other activities which involve exposure to radiation, except for that received for medical or dental diagnosis, or medical therapy.
Personnel monitoring equipment: Devices designed to be worn or carried by an indi-vidual for the purpose of measuring the dose received (e.g., film badges, pocket chambers, pocket dosimeters, film rings, etc.).
I Rad (roentgen absorbed dose):
A measure of the dose of any ionizing radiation to any medium in terms of the energy absorbed per unit mass of the medium. One rad is the dose corresponding to the absorption of 100 ergs per gram of any medium.
Radiation: Gamma rays and x rays, alpha and beta particles, neutrons, protons, high-speed electrons, and other nuclear particles; but not sound or radio waves, or visible, infrared, or ultraviolet light.
Radiation area:
Means any area, accessible to personnel, in which there exists radiation at such levels that a major portion of the body could receive in any one hour a dose in excess of 5 mrem or in any 5 consecutive days a dose in excess of 100 mrem.
Radioactive material: Any material which emits ionizing radiation spontaneously.
Radioactivity: That property of a substance which causes it to emit ionizing radiation.
It is measured in terms of disintegrations per unit time or curies.
Radiography:
The examination of the physical structure of materials other than human beings or animals by nondestructive methods utilizing radiation.
Relationship of Rem to R and Rad:
Rem = R x RBE = Rad x RBE.
Relative biological effectiveness (RBE): A f actor that compares, for the same energy absorbed per unit volume, the biological effect or the various types of radiation.
Approximate (most conservative) values of RBE are:
X-ray 1
Gamma 1
Beta 1
Neutron (thermal) 5 Neutron (f ast) 10 Alpha 20 REM (roentgen equivalent man):
REM is a measure of the dose from any ionizing radiation in body tissue,in terms of its estimated biological effect relative to a cose of 86
i a
k one roentgen (R) of x-rays. The relation of the rem to other dose units depends upon the biological eff ect under consideration and upon the conditions of the irradiation.
Restricted area:
Any area to which access is controlled by a licensee for protection of individuals f rom exposure to radiation and radioactive materials.
Roentgen (R):
A term used to denote x and gamma-ray doses only. One roentgen (R) is that amount of radiation that produces one electrostatic unit of charge of either sign per cubic centimeter of dry air at STP. This is equivalent to the production of 83 ergs per gram of dry air.
Scaled source:
Any radioactive material permanently encapsulated in such a manner that the radioactive material will not be released under the most severe. conditions likely to be encountered.
Special nuclear material:
Plutonium, uranium enriched in the isotope 233 or 235; or 1
any material artifically enriched with any of the foregoing, and Cf-252 (accountability purposes).
Survey:
An evaluation of the radiation hazards incident to the production, use,
(
release, disposal, or presence of sources of radiation under a specific set of conditions.
(
When appropriate, such evaluation includes a physical survey of the location of l
materials and equipment, and measurements of dose rates, doses, and quantities and
[
concentrations of radioactive material.
I
~
87