ML20205T750

Detection & Skin Dose Evaluation for Characteristic X-Ray in Activation Product Contamination

ML20205T750
Person / Time
Site:	Palisades, Big Rock Point, 05000000
Issue date:	11/04/1988
From:	English R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:
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ML20205T740	List: ML20205T736 ML20205T750
References
NUDOCS 8811140376
Download: ML20205T750 (9)

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l ATTAC10fENT Consumers Power Company Big Rock Point & Palisades Plants Dockets 50-155 & 50-s55 DETECTION AND SKIN DOSE EVALUATION FOR CHARACTERISTIC X-RAYS IN ACTIVATION PRODUCT CONTAMINATION November 4, 1988 i

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8911140376 881104

+1DCIC K 0500 5 8 Pages OC1188-0194-h104

j CETECTION AND OKIN DOSE EVALUATION TOR i

CHARACTERISTIC X RAYS IN ACTIVATION PRODUCT CONTAMINATION t

f R. A. English and N. A. Campbell )

Censumers Power Company [

Jackson, Michigan  !

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AISTRACT F

A skin dose rate conversion factor of 2.3x10 4 oCy h 8 (2.3 x .

10 3 mrad /hr) per cpe has been determined for the 5.9 kev  !

x rays of HTe when using a pancake C.M. probe 1.3 ca fram the i source. This value is within lot of values found for common  !

beta esitters and suggesta that a single conversion factor is i L

suitable for estinating skin dose when contaminations seit x rays, betas or sistures of both. Other detectors respond I differently to betas and z rays which makes it necessary to [

determine x ray contribution to provide accurate dosimetry.  !

A staple method for determining this concribution in a sized ,

field has been developed which uses a pancake probe with 75ag  ;

ca.: aluminua and polyethylene abrerbers. The technique j eliminates the need for specific nuclide analyses which are e difficult for isotopes which decay only by electron capture. (

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INT *0 DUCTION Although x ray energies from these nuc. [

lides are in the range of 5 to 7 kev, l The largest component of activity in low they exhibit aloninum absorption charac. l 1evel reactor waste is reported to be teristics cia 11ar to beta emitters with {

55 Fe (Cruhlke,1986. Manion and average energies in the range of 150 to (

LaGuardia, 1976). Iron.55 decays solely 300 kev. stus, simple aluminue absorber by electron capture and eetts 5.9 kev plots will not differentiate between characteristic x-rays. Other x-ray these x rays and the botas free other  !

emitters include 51Cr, 56 ,,, 57Co 3'Co, contamination sources such as 60g ,,

N1. As with 557 ,, 59,g ,g,,g,,g, 59 and genna emissions, which complicates Because characteristic x rays are difft.

identification and quantification, cult to identify and normally represent I such a small component of the total [

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R. A. ENGLISH AND N. A. CAMP 8 ELL energy fluence, they normally are This paper describes the research per.

ignored in external dosimetry calcula. fot1 sed to determine C.M. pancake nrobe tions. However, unlike betas of equally skin dose conversion factor for "Te low energy, these z. rays will penetrate characteristic x. rays, and a simple easily to the basal layers of the skin, field method to estimate x ray fluence and should be considered in skin dose rate in the presence of botas. Civen calculations if present in significant the ability to estimate z. ray emission quantity. rates, the response of other detectors and seasuring devices to x rays may be It is cosmon practice to utiltre a C.M. evaluated and appropriate dosimetry pancake probe for evaluating personnel calculattens performed.

contamination, either alone or in con.

junction with wholebody ir partial body METHODS AND MATERI.uS frisking booths. The pancake probe, at a fixed distance from skin. Provides A source of N Te was obtained* with a ,

for consistency in contamination level total activity of 3.7 MBq (100 uC1) e documentation and reporting. If the 201. Acti's area of the source has a contamination is later lost in the diameter of 1.0 ca. Activity is depos.

decontamination process, the ited between rvo aluminised nylar films pancake probe count rate may be the of approximately 1 eg ca.8 in the only data available for dose evalua. center of a 2.54 cm disseter ring, tion.

taission rate of 3.9 kev x rays was It has been reported (Flood. 1988) that determined using an z. ray yield of 261 for beta eettters with energies suffi. (0111asa and Von der Lage. 1975).

cient to provide skin dose at 0.07 as Fluence rates and dose rates at various tissue depth, the HP.260 pancake probe distances in air and at a 7 as ca.8 responds with relatively constant skin depth in tissue were calculated using dose conversion factors between 1.3x published attenuation and energy absorp.

10*' and 2.1x10 acy h*I (1.5 x 10 8 tion coefficients (Hubbell, 1982),

and 2.1x10 8 arad/hr) per cpe for Fluence rate at a given point is beta contamination on the surface of calculated as follows:

the skin. (1) y = (A)(Y)(EXP.((u,)(x,)+(u g)(a gD UC

• E. I. Du Pont de Nemours & Co., litterica. MA 01862 2

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A. A. ENGLISH AND N. A. CMf78Ett klere I T = fluence rate (z. rays s ca 8) Detector systems used were Ludlus Model A = sq (disintegrations per second) 177 Rate Meter with NP.260 probe'.

j Y = photon yield (0.26 x rays per teerline Model R0 2 ten chamber rate. ,

i disintegratica) setert and dysprosium activated calcium j

u, u, = attenuation coefficients for sulfate thetsoluminescent dosimeters

{

l aylar end either air or t$ssue (CaS0g (Dyl TLD's)=.  ;

(ca8 g*I) x , x, = attenuator thickness, sylar and Absorption characteristics of both the N Te source and a hot particle ahewn to

! either air or tissue tg ca.8) 60 l C = geometry factor be nearly 2001 Co by gasuna spectral I j (4ea8/In((h8+a8)/h81) for analysis were seasured with the pan.

j detectors: 2.0 for skin contact) cake probe for polyethylene and stunt. {

! a = .ource radius (ca) num. This analysis was performed to ,

h = source to detector distance (en) check the N ye source for photon purity f

j by cceparison with published attenus.

[

l Dese rates in air and tissue are cal. tion coefficients (Hubbell. 1982). The i culated in accordance with Equation 28 data also verified that betas could be f j diettaguished fres z rays using these j

) D = (T) (T) ( E) (1.E.KP ( .ux) 1/ (C ) (a) (2) two ccanon asterials. l

smere.

D = dose rate (gy h*I) RISULTS f

7 = time conversion (3600s h*I) (

) T = fluence rate (s. rays ca.8 s *I) Detector Response [

E = energy per u. ray (3.9:10 8 r(eV)  !

u = energy absorption coefficient Fluence rates at 6.3 cm and 6 ca in air f

(cn8 g *I) and at 0.07 sus skin depth are listed in

{ x = density thickness of thin layer Table I along with calculated dose f at dose point (g es*8) rates.and detector responses for the I C = energy to dose conversion S.9 kev a. rays of N Te. Efficiencias .

! (6.242:10' MeV g.8 Cy*l) and dose rate conversion factors are f i a = mass in 1.0 cas of layer a at also given. The dose rate conversion [

dose point (3) factor with NF.260 probe face to source {

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, distance at 1.3 cm (n inch) is 2.):10*'

nGy h*I (2.3:10 8 arad/hr) pee cra, l

) a tuclum Measure, ente. Inc., sweetvater. Tx ren6 [

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+ Eterline Instrw ents Corp.. Santa Te. !E 57501 l = Teledyne Isotepos. Vestvood. NJ 07675  !

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R. A. ENGLISH AND N. A. CAMFRELL Table 1 ,

Calculated Fluence and Cose Rates y,i Detector Response for 5.9 kev X.raye i LOCAT10.9

• SKIN 2.4cm 2.7cm 4.3cm 6.0cm 4.0x10 I 1.2 10' 9.5 108 3.57108 1.8:108 l T1uencera}et (s. rays s* ca.8)

Doserege 2.8 10 I 8.8:10*I 6.9:10*I 2.6 10*1 1.3 10*I l (acy h* )

HP.260 (cpa) - l'.2 10 5 g,,,gg e . 2.9:10' '

(Efficiency)ts . 1.0! 0.91 - 1.61 i (Dose C.T.)* . 2.3:10*4 3.1x10'4 . 9.7x10*'  ;

i R0 2 (ocy h*I) . . . 1.5 10.* 6.5x10.a ,

(Efficiency) . . . 361 493 l (Dose C.F.)* - . . 1.9:108 4.3x108 l

- . . - 3.7 10*'

BareTLp)

(aCy h*  ;

(Efficiency) . . . - 2801 [

. . . . 2.7x10*I i 783TLp)

(acy h* (

(Efficiency) . . . . 200%  !

• Tactor times reading to give skin dose rate (mCy h*I) I

" Distance to center of detector .

+ Center of detector, perpendicular to source

" *1.63 411 locations if fluence rate is averaged over full detector ares '

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Efficiency of the R0 1 in the open The CaSog (Dy) T1.D's responded with an '

SS III I window ac.de to Te s. rays is apprest. effi tency of 1401 reistive to Cs sately 493 with chamber conter at 4 cm when esposed bare (no holder), and with j free the source, and approntaately 561 an efficiency of 1101 relative to 88'Cs  !

at 4.3 cm (4.3 cm represents the ty?1 when esposed in a Teledyne 18 3 holder j f cal 4. inch source to windev distance with a beta window of 7 og ca.8 of used in field seasurements). It would sylar. R wever, unless it were known II be well within the accuraty of the that the badge had been esposed to Te ,

tessurements to assige, a value of $0! a. rays, the respoese vould be identified [

! t i both distances. A more significant as a beta exposure and dose assigned  !

206 vatistien occurs when comparing read. based on T1 calibration. Dose f ings with dose to one square centtneter reported as beta esposure would be 2001 f j of skins the reading is 0.53% of skin of actual under these circunstances. l dose at 4.3 cm (c.T = 190) and 0.231 f

at 6 cm (C.T.= 450), j I

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R. A. ENGLISH AND N. A. CAMPBELL Attenuation Attenuation results for "Te x-rays and The polyethylene absorber curves of 60 Co hot particle batas are presented Figure II also indicate a half-value for aluminum and polyethylene absorbers thickness of approximately 7 mg em 8 60 in Tablo II. Transmission curves are for Co betes, but a much greater value (75 mg en 8) for N Fe x-rays.

plotted in Figures I and II, Table II Attenuation of 55 Fe X-rays and 60 Co Beta Radiations with Aluminum and Polyethylane Absorbers A3SOR3ER gt:MINL'M (p)* P0pTHYLINEjcM*5 (mg co 8) Co Te Co Fe 0.0 10,000 10,000 10,000 10.000 3.0 7,800 7,700 ** **

6.7 4,700 4,200 ** **

9.3 ** ** 4.300 8,700 18.6 ** ** 2,600 8,100 20.7 1,600 850 ** **

27.9 "* ** 1,150 7,100 37.5 ** 160 810 6,800

55. ** 15 810 5,800 74.4 ** 0 810 4,800 112 810 ** ** 3.200 200 ** ** ** 1,500 ,

420 ** ** ** 200 490 720 ** ** **

• Measured count rates nocualized to 10,000 cps with no absorber.

• • No measurement made.

60 The aluminum absorber data shows that Assin, for Co the same gama com-both 60 Co botas and N ye x-rays exhibit ponent as seen with aluminum remains half-value thicknesses of approximately here after the betas are gone.

7 ug em 8 At e density thickness of 75 mg en 8, aluminum is essentially The observed half-value thicknesses for opaque to either, although a gasmaa N Fe agree well with published values residual remains in the case of 60.C o . ('.tubb ell, 1982 ) for attenuation coeffi.

No residual remains for $$Fe which cients at 6 kev: 113 cm8 ge *I for alumi-indicates that the source is not con- num (half value = 6.1 mg ca 8) and 9.1

• 1 taminated with any significant amount em8 gm or polyethylene (half value =

of gamma or high energy beta saitters. 76 mg en 8).

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R. A. ENGLISH AND N. A. CAMPBELL 100-t *d

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4 'f 5.0  : ';; $- 1 i i 2 i I

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db *  ! . 9 0 1.0 'f 9 60 co

=

3 1.0 - i5 E 8 g g ,I

' A 557 , ,C 0.5 - , 0.5 0 60e ,

i i . ",e 1 8 100 2D0 3@ 600 506 tdo 260 30b 6N $N Aluminum icknees (as ca* ) Polyethylene thicknees (as ce*)

Figure ! - at6enuatic.;. by Altaninus Figure !! - Attenuation by polyethylene Since the aluminum absorber fiiters out For the pancake probe, Jose rate conver-all chsracteristic x-rays, but responds sion is independent of whether counts very much as polyethylene to betas and are from x rays or betas (gamma back-the higher gasuna energies, uesaurements ground may be conservatively ignored, behind the aluminum absorber provide an or may be subtracted as count rate I excellent "background" for gasuna and behind a 1 g ca 8 absurber). However, any high energy betas penetrating the if correction of personnel TLD's or polyethylene absorber. Count rate other devices for characteristic x ray behind the aluminun shield, subtracted response is required, x-ray and beta from the rate behind the equal density components of dose should be computed thickness polyethylene, gives net count separately. The following equations rate due to x rays. The tse of 75 mg describe one method of providing such l em 8 absorbers allows this x-ray count analysis rate to be saltiplied by a factor of two (due to 502 attenuation at this D, = (2.0)(CpCg)(2.3x10*') (3) thickness) to give the unshielded count rate contributed by x-rays. D b = (C Cg )(2.3x10*') - D, (4) or:

D b = (2.3x10 ')(C+2 g -2C p gC) ($)

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e R. A. ENGLISH AND N. A. CAMPBELL Where: Instrument geometry variations under field conditions (note variations of D* = dose rate free x-rays (mCy h*I) data in Table I with distance) are ex-Db = dose rate from betas (mGy h*1) pected to be by far the largest Cp = count rate behind 75 mg ca.: variable in application of this data, polyethylene (cpm) Where readings with multiple instruments Cg = count rate behind 75 as en 8 were performed (in jigs to minimize aluminum (cpe) geometry variations), standard devia.

C= count rate with no shield (cpe) tions of the measurement means were cc = (optional) count rate at 1 3 ca 8 typically in the range of t101 to 151.

(eps) Under normal field circumstances, [

2.3x10*' = skin dose rate conversion accuracy to within *25! would be con-factor for probe at i inch sidered good.

(mCy h"1 per eps)

Characteristi,c x-rays from other than The same technique may be applied using 58Fa are known to be present in con-an R0-2 Lon chamber to determine either tamination materials because gamma dose in air or dose to skin by using spectral analysis often indicates the appropriate data (efficiency or significant amounts of $1Cr, I'Mn and ,

58 or skin dose rate conversion factor, Co in such samples. However, we 55 respectively) from Table I. We find believe that Fe data is appropriate that it is appropriate to use an ion for use in the general case because the chamber rath,ev than the pancake probe x-ray energy is at about the mean of and Ludium 177 Rate Meter when count energies for the other nuclide:1, and rates exceed approximately 100,000 cpe, because $$ F e ie believed ce he the x-Above this level, ion chamber readings ray esit'.tr of highnt abnE4We in generally are more accurate than those most activatim phe concatanation. l of the pancake probe for which signi-ficant dead time corrections must be CONCLUSIONS applied.

55 Characteristic x-rays from Fe and DISCUSSION OF ERRORS cther ccinon activation product x ray smittats nay L. treated as beta Field instruments were uses for this particles when tonverting pancake probe study. Daily calibration checks ar.: ecunt, rates to skin dose rate. A fac-performed to confire response variation tor of 2.3x10*' inGy h*1 (2.3x10 8 mead /

no greater than *20% of a known ru ding. hr) per cps from x rays has been deter-

! The $5Fe source also is known w t'01, 4 r.ined for this coaversion.

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R. A. ENGLISH AND N. A. CAMPBELL Some detectors such as the CaSO 4(Dy)TLD Less than 0.1% of characteristic x-tested in this study do not provide tis- rays at 5.9 kev penetrate through 75 sue equivalent response to characteris- mg cm 8 of aluminum, yet 50! will tic x-rays. These detectors require penetrate through 75 mg en 8 of poly-response correction when measuring x- ethylene. Equations presented in ray dose. Aluminum and polyethylene this report allow use of such absorbers absorbers provide a convenient way of in the field to identify presence of determining x ray contribution to a characteristic x-rays and to determine detector. their contribution both to detector response and to dose.

REFERENCES Dillman, L.T. and Von der Lage, F.C. Chruhlke, J.M. EPA Source Term for Low-Radionuclide Decay Schemes and Nuclear Level Radioactive Waste Risk Assess-Parameters for Use in Radiation-Dose ment Draft Report. Office of Radia-Estimation. MIRD Pamphlet No. lo s 1975. tion Programs US Environmental -

Protection Agency, Washington, DC 20460:

Flood, J.R. Determinatioa of Dose Equi- 1986.

valent Due to Radioactive Contamination of Skin. Presentation at Hot Particle Hubbell, J.R. Photon Mass Attenuation Workshop, San Francisco, CA: 1982, and Energy Absorption Coefficients from Available from: Tennessee Valley 1 kev to 20 MeV. Inc. J. Appl. Radiat.

Authority, Office of Nuclear Power, Isotop. Vol. 33, pp 1269-1290: 1982.

Chattanooga, TN 37401.

Mauton, W.J. and LaGuardia. T.S. An Engineering Evaluation of Nuclear Power Decommissioning Alternatives. Atomic Industrial Forum, 41F/NESP-009: 1976.

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