ML20147C386
| ML20147C386 | |
| Person / Time | |
|---|---|
| Issue date: | 01/31/1997 |
| From: | Steven Baggett NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Rowe L AFFILIATION NOT ASSIGNED |
| References | |
| SSD, NUDOCS 9702060157 | |
| Download: ML20147C386 (2) | |
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l' nos UNITED STATES j
NUCLEAR REGULATORY COMMISSION
\\.....[t WASHINGTON, D.C. 206 % 4001 January 31, 1997
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Mr. Larry Rowe 1837 S. 50ct.
Cicero,IL 60804
Dear Mr. Rowe:
l In response to your question regarding the safety of Kr-85, Kr-85 is primarily a relatively low energy beta emitting noble gas. When used in conjunction with most gauging devices, the Kr-85 gas is contained in a seaicd capsule. During normal use, the Kr-85 poses very little risk.
The gauges using these Kr-85 source capsules are usually constructed such that, if used properly, the outer shell of tha gauge shields the user from radiation exposure from the source.
If the source capsule should rupture, the gas disperses quickly, providing a very small risk of radiation exposure. Since it is a noble gas, it does not chemically react or ccmbine with other matenals. If the gas was inhaled, it would be readily exhaled, posing little risk. Since the radiation from these source can penetrate human tissue to approximately 3 millimeters, prolonged exposure to the source capsule without any shielding (such as holding the actual 1
source capsule in ycur:tand), could result in skin damage. I have enclosed a copy of a booklet entitled, " Working Safely with Nuclear Gauges" (NUREG/BR-0133, Rev 2). This booklet provides some additionalinformation related to radiation and safety. For gauges such as the Aeonic gaup.is that you mention, NRC regulations relate 1 roentgen to 1 rem. Please note that the prefix "miili " is used in the SI system (Intemational System) to divide a standard unit of measurement into smaller units. For example, there are 1000 millirems in 1 rom, or 1000 i
millimeters in 1 meter. You could also say that 1 millirem is the same as 1/1000th of a rem, or 1 millimeter is the same as 1/1000th of a meter.
The following definitions are provided in order provide you with additional information on how the units of roentgen, rad, and rem are related.
The roentgen (abbreviation, R) is a unit of measure for exposure (X). The quantity exposure describes an x-ray, gamma ray, or high energy beta ray field. It is e measure of the amount of ionization produced in air.
The radis a unit of measure for absorbed dose (D). The quantity absorbed dose is the e. mount of energy absorbed (or dose) per unit mass of material due to an exposure. The value of the 1
absorbed dose for a given exposure depends on the material. For air, there would be a 0.87 rad absort>ed dose in the air for an exposure of one roentgen. For human tissue, a person would receive approximately one rad absorbed dose for an exposure of one roentgen.
The remis a unit of measure for dose equivalent (H). It is related to the amount of biological damage to man from a given exposure to radiation. The NRC regulations use the dose i
equivalent when limiting allowable limits for exposures to humans. If you know the dose in rads, you can find the dose equivalent in rems, by multiplying the dose by a number called the
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quality factor. The values of the quality factor reflect the ' relative amount of cell damage that the different types of radiation are thought to cause. For example, radiation from alpha rays are thought to do 20 times as much damage as radiation from x-rays, beta rays or gamma rays do for a given energy. The reasoning for this is that x, beta, and gamma rays give their snergy over a longer distance (distributes its energy ~over more cells, so less damage in each cell), and alpha rays give their energy over a short distance (distributes its energy in fewer cells, so more i
damage in each cell). For x, beta, and gamma rays,; NRC regulations use a quality factor equal to 1; therefore,1 rad relates to 1 rem.
In relating the units of roentgen an' ' rem, remember that,in human tissue, an e pesure of one d
roentgen would result in an absorbed dose of approximately one rad. Also, for gamma rays, x-rays, and beta rays, using a quality factor equal to 1,1. rad relates' to i rem. Putting these facts together, you can say that, for gauges emitting beta or gamma rays, such as the Aeonic gauges, one roentgen relates to one rem, undsr NRC regulations.
If you have any questions, please ccntact me at (301) 415 7273.
Sincerely, l
Ost'giel SfsneS W f
i Steven L. Baggett, Chief
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l Sealed Source Gafety Section Medical, Academic, and Commercial l
Use Safety Branch Division of Industrial and Medical Nuclear Safety l
Office of Nuclear Material Safet/
l and Safeguards
Enclosure:
NUREG/BR-0133, Rev 2 l
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