THE HANFORD THERMOLUMINESCENT MULTIPURPOSE DOSIMETER*

*. :. .

, .'4

L. F. Kocher, G; W. R. Endres, L. L. Nichols

D. B. Shipler,** and A . J. Haverfield

Bat te l le Pac i f ic Northwest Laboratory Richland, Washington 99352

May 28, 19'11

I report was prepared a* a~wuf i t o( v f d '

sponsored by the United States Govement. Neither the United States nor the United States Atomic E n e m Coxnmbion, nor any of theif employeeil, nor any of

1

theif c a t r ~ ~ t o t ~ , subcontractors, or their employe=, 1 makes any warranty, exprso or implied, or assumes any legal ability or responsibility for the sccurrcy, con- 1 pleten& or usafulnC1B of any I n f o ~ a ~ o n , appluatu~, product or process &-d, or n p m ~ n t s that its use 1 would not infringe privately owned ri&b.

I

*This paper is based on work performed under United S ta t e s Atomic

Ener&y Commission Contract ~~(45-1 ) -1830 .

**Present address : oreion Technical I n s t i t u t e , Klamath Fa l l s , Oregon 97601.

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

DISCLAIMER

Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

THE HAWORD THERMOLUMINESCENT MULTIPURPOSE DOSIMETER*

L. F. Kocher, G. W . R . Endres, L. L. Nichols, D. B. Shipler,** and A. J. .Haverfield

B a t t e l l e Memorial I n s t i t u t e P a c i f i c Northwest Laboratory Richland, Washington 99352 '

ABSTRACT

A five-element thermoluminescent dosimeter f o r b e t a par-

t i c l e s , photons and neutrons has been developed using LiF blocks.

7 One LiF b1.ock i s shielded t o provide i n t e r p r e t a t i o n of t h e one

7 centimeter t i s s u e depth dose. A second LiF block i s unshielded

6 t o provide t h e derma dose i n t e r p r e t a t i o n . , Two LiF and one 7 ~ . i . ~

'

,blocks a r e used f o r f a s t and thermal neutron dose i n t e r p r e t a t i o n .

. The accura te response of t h e dosimeter t o t h e wide v a r i e t y of

r a d i a t i o n sources a t Hanford makes it a good replacement f o r t h e

Hanford f i l m badge f o r rou t ine personnel dosimetry.

*This paper i s based.on work performed under United S t a t e s Atomic Energy Commission Contract ~ ~ ( 4 5 - 1 ) - 1 8 3 0 .

HPresent address: Oregon Technical I n s t i t u t e , Klamath F a l l s , Oregon.

I . INTRODUCTION . . . . . . . . . . . . . . . . . . . 1

. . . . . . . . . . . . . . A Physica l Descr ip t ion

B . Thermoluminescence of Mastic Coated . . . . . . . . . . . . . . . . . Teflon Tape

. . . . . . . . . . . I1 . BETA ATJD PHOTON DOSIMETRY

. . . . . . . . . . . . A Theory and Descr ip t ion . . . . . . . . . . . . . . B Photon Energy Kesponse

. . . . . . . . . . C Angular D i s t r i b u t i o n S tud ies

. . . . . . . . . . . D Mixed Radiat ion Exposures

. . . . . . . . . . . . E Spec ia l F i e l d Studies

. . . . . . . . . . . . . . . . I11 NEUTRONDOSIMETRY

. . . . . . . . . . . . . A Theory and Descr ip t ion

. . . . . . . . . . . . . B Fading and Annealing

. . . . . . . . . . . C Neutron Energy Response 22

D . Effec t of Dosimeter Wearing Pos i t ion . . . . . 22

E . Mixed Radiat ion and Spec ia l F i e l d S tud ies . 25

. . . . . I V . 6 7 . .

ANNEALING AND FADING OF LiF AND LiF 30

. A . Theory . . . . . . . . . . . . . . . . . . . . . 31

. . . . . . . . . . . . . B Exper imenta lResul ts 32

. . V: CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . 38

. . ' V I . AC~?O~%EDGE~\IENTS. . . . . . . . . . . . . . . . . . . 40

. . V I I . REFERENCES . . . . . . . . . . . . . . . . . . . . 41

. . . . . . . . . . . . . . . . V I I I FIGURE CAPTIONS ; 43

THE HANFORD THERMOLUMINESCENT MULTIPURPOSE DOSIMETER*

L. F. Kocher, G. W. R. Endres, L. L. Nichols, D. B. Shipler, and A. J. Haverfield

I. INTRODUCTION

The phenomenon of thermoluminescence has been studied in.great . detail by Kocher and Endres at Hanford and other people throughout the

world since 1964. (ly2) Until that time, it had remained essentially a

scientific curiosity. In the two or three preceeding years John Cameron

at, the. University of Wisconsin solved the problems of doping lithium

fluoride'in a manner which provided sufficient sensitivity to,radiation

so that the material could be used in personnel dosiine'try.

Most investigators feel that lithium fluoride ( ~ i ~ j is the best

. . material to use for personnel dosimetry. (.3) The beta-photon work conduc-

ted at Hanford has been concentrated on nearly pure 7 ~ i ~ materials.

( 4 The 'thermoluminescent properties of LiF as measured by Endres

are nearly independent of the incident photon radiation energy, and this

property makes it suitable as a replacement for the health physics film . '

. . badge. . The sensitivity of LiF relative to soft tissue is flat within 10

percent for photons from 10 Rev to 10.MeV(5) so that a multi-element array

of LiF crystals with suitable filters can act as a simple spectrometer as . .

well as an accurate dosimeter.

*This paper is based on work performed under United States Atomic Energy Commission Contract ~~(45-1)-1830.

. , . .

A. Physical Description

This section describes a beta-photon thermoluminescent personnel

dosimeter badge to replace the Hanford film badge(6) for routine personnel

monitoring. The dbsimeter makes us$ of the many unique properties of LiF

crystals. An exploded view of the dosimeter badge is shown in Figure 1.

The multipurpose card which houses the TL blocks measures 7.8 cm

x 3.8 .cm x 0.1 cm an3 weighs 3.6 .grams. The IliF TL blocks are eoktained

- 2 in Teflon TFE skived tape that is 0.005 cm (12.2 mg/cm ) on the front side

2 of the block and 0.009 cm (16.0 mg/cm ) thick on the back and positioned

at the center of five 0.95 cm diameter holes in the dosimeter card. The

tape on the back side of the card is coated oc one side with pressure sen-

sitive silicone polymer adhesive. The adhesive retains the TLD blocks so

that when they are placed in the center of these holes, they remain in po-

sition. The Teflon TFE tape on the front side is not coated with an adhe-

sive for reasons discussed later. This semi-transparent tape used for

securing the blocks allows the thermoluminescent crystals to be read out .,

without remo.ving the blocks from the dosimeter card. The dosimeter card

is injection molded from a thermoplastic resin' which has a specific gravity

of 1.06 and a heat deflection of 130'~. This material was chosen over a

metallic holder because of cost and convenience. The plastic card can

easily be identified by mechanically punching identification numbers or

letters in the card. 'l'he whole system lends itself to convenient, automatic

prucesslng. ,The card has been designed to permit insertion into the holder

in only one orientation.

. .

. . . .

The dosimeter holder i s i n j e c t i o n molded from styrene-butadiene-

a c r y l o n i t r i l e ( c ~ c o l a c ) and i s designed t o hold t h e dosimeter card and t h e

Hanford s e c u r i t y c r e d e n t i a l and appropr ia te f i l t e r s f o r t h e blocks a s

shown i n Figure 2. The holder measures 8 cm x 4 .5 cm x 0.6 cm and weighs

22.5 grams. The 1.27 cm diameter f i l t e r s a r e r e t a i n e d i n c a v i t i e s i n t h e

holder with an adhesive and covered wi th mylar t a p e . When t h e dosimeter

'Y card i s i n s e r t e d i n t o t h e ho lde r , a snug f r i c t i o n f i t i s obtained and each

TL block i ~ ' centered between the ' appropr ia te f i l t e r ma te r i a l s ., The physi-

c a l c h a r a c t e r i s t i c s of t h e f i l t e r systems a r e shown i n Table I.

TABLE I

FILTER SYSTEM - PHYSICAL CHARACTERISTICS

Diameter Thickness To ta l . F i l t e r # Shie ld . i r ~ cm. i n cm. mg/cm2

1 Open Window 0 .95 0.0 0

Teflon TFE Tape 0.005 12 . . .

2 Cycolac 1 .27 0.089 93

Aluminum 0.064' 173

Mylar 0.007 7

Teflon TFE Tape 0.005 12

3 Cycolac '. 1.27 0 , 051 5 3

Tin 0.102 7 50 . .

Mylar 0.007 7

Teflon TFE Tape 0.005 . 12

4 Cycolac 1.27 0.051 . 5 3 . .

Tin 0.051 37 5

Cadmium 0.051 440 - Mylar,, . . . , 0.007 7

~ e f l o n TFE 'Tape 0.005 12

5 Cycolac 1.27 0.051 53 Tin

Mylar

Tef lo r TFE Tape

-4- . - . .

At Hanford, an additional thickness of plastic and paper is

placed over the filter system and open window in the form of a security

credential. The credential is 0.076 cm thick and has a density thickness

Thermoluminescence of Adhesive Coated Teflon Tape

One of the major considerations in the design of aTLD system . . . v

must be the operating costs involved in processing several thousands of

TLDs on a routine basis. When the TLZ) material is mounted in a permanent

housing, then automatic reading and handling makes the operating costs

of the system minimal. . .

One TLD system utilizing a single 7 ~ i ~ block has been implemen-

ted at Hanford . (7) This report describes a more complex system utilizing 6 7 both LiF and LiF blocks which is in the process of being implemented.

Both systems use 0.32 cm x 0.32 cm x 0.089 cm LiF blocks sandwiched between

two pieces of Teflon tape and mechanically fixed in a two-piece, injection

molded, thermoplastic card. Readout.is'accomp1ished by positioning the

dosimeter card under a photomultiplier tube 'and heating the TL block with

a constant temperature, circular heater 0.55 cm in diameter. !Fhe employee

identification number is punched in the card so that readout and identifi-

cation are accomplished without removing the TL blocks from the card.

Considerable attention has to be given to the properties of the

cs.rd and tape ualerials. Mechanical properties not withstanding, the ther-

mal and thcrmol~uinescent properties are of prime importance. A number of

plastics were investigated as to their heat deflection and thermoluminescent

response. The c r i t e r i a f o r t h e f i r s t an ford TLD badges were not as

s t r i n g e n t a s f o r t h e second because of the ' lower readout temperature of

' L ~ F (250'~). t he heat ing of t h e card near t h e TLD and t h e heat ing o f .

. t h e t ape were not .as c r i t i c a l a t . t h i s lower temperature. It was found . .

t h a t even t h e color ing pigments i n t h e card changed t h e thermolumines-

., . . cent p roper t i e s and p l a s t i c was se lec ted t o minimize t h i s e f f e c t . . Many, . .

brands and types of adhesive coated Teflon t a p e were t e s t e d and t h e tape J

with t h e h ighes t heat de f l ec t ion ' and l e a s t thermoluminescence was chosen.

Af ter some t e s t i n g of t h e f i r s t TLD system, it became apparent t h a t t h e

Teflon t a p e was a l s o s e n s i t i v e t o u l t r a v i o l e t l i g h t . This s e n s i t i v i t y

was apparent only a s a v a r i a b i l i t y i n t h e readings of con t ro l cards and . .

was controll'ed wi th jn acceptable limits by s t o r i n g t h e cm-ds i n t h e dark

and minimizing f luorescent l i g h t i n g and other ul-1;raviolet exposures during

reading and handling procedures.

, The second system develdped a t Hanford included GL blocks of 6 L i ~

f o r neutron dosimetry. A s indica ted i n o the r papers, ( 8 ' 9 ) t h e most appro-

p r i a t e readout temperature f o r neutron induced thermoluminescence 'is 300°C.

When.studies began on t h e prototype badges using t h i s temperature, it was

immedia.tely apparent thxL t h e thermoluminescence of t h e tape became more

s i g n i f i c a n t and a more d e t a i l e d study of i t s p roper t i e s was i n order .

The f i r s t discovery during t h i s .s tudy was t h a t t h e thermolumines-

cence was pr imar i ly t h e property of t h e adhesive and not t h e TFE Teflon tape

used i n t h e cards . A v a r i e t y of t r ansparen t and semi-transparent t apes and

adhesives were inves t iga ted and a l l those adaptable t o t h i s app l i ca t ion had

thermoluminescent p roper t i e s equal t o o r g r e a t e r than t h e adhesive coated

Teflon t a p e i n use. ' The. re.sponse of two pieces

a s a funct ion of temperature i s shown i n Figure

of new tape , s tuck t o g e t h e r ,

3 , Curve A . It can be seen

t h a t t h e .adhesive thermoluminescence i s not a major problem a t hea te r tem-

pe ra tu res up t o about 250°C. A t temperatures above 250°C, more luminescence

i s re l eased and t h e s lope i s q u i t e s t e e p , making background readings of t h e

TL blocks t o o l a r g e and v a r i a b l e t o meet design c r i t e r i a . The f luorescen t

spectrum from t h i s Teflon ' t ape adhesive i s a broad band emission feom 300 I

nm t o 650 nm with t h e maximum at about 500 m. This spectrum overlaps t h e

f luorescen t spectrum from LiF, which is a broad band emission wi th a maxi-

mum a t 400 m.

A number of othe'r techniques of r e t e n t i o n of t h e TL blocks i n t h e

cards were inves t iga ted before a success fu l mockup badge was a t t a i n e d . The

compromise assembly was made of one p iece of adhesive coated TFE Teflon

t a p e and one p iece of p l a i n TFE Teflon t a p e . This sandwich maintained t h e

mechanical i n t e g r i t y of t h e block p o s i t i o n i n t h e card and made assembling . ..

t h e sandwich much e a s i e r . It was found t h a t a complete readout of t h e TLD

could be accomplished without adhesive f luorescence by hea t ing t h e sandwich

on t h e p l a i n t a p e s i d e wi th ' t h e hea te r - a t a temperature of 300°C f o r a

period of 20 seconds. I

The response a t var ious temperatures f o r an unexposed 7 ~ i ~ block . .

i n t h i s sandwich a r e shown i n Figure 3, Curve ' B . These r e s u l t s - i n d i c a t e

t h a t during t h e hea t ing cyc le , t h e temperature d i f f e r e n t i a l across t h e , .

block i s never l e s s than 3 0 ' ~ . This d i f f e rence i s enough t o preclude most

of t h e readout of t h e adhesive on t h e o the r t ape .

. . Additional studies were made to determine the ultraviolet sensi-

ti+ity of this adhesive. Cards were exposed for various times to an ultra-

violet lamp and read out at various temperatures. Three of these runs are

' . shown in Figure 3, Curve C. These and other handling studies us,ing fluo-

rescent. room lights indicate that the ultraviolet induced thermoluminescence

of the tape adhesive accounts for about 30 picocoulombs of background for

normally handled cards as can be seen by comparing Figure 3, Curves A, B, *

and C. Studies using a readout temperature of250°C show that cards .pro- Y

cessed in normal room light conditions had an average background of 73,

picocoulombs, cards processed with' no exposure to room light had an aver-

age background of 42 picocoulombs and cards exposed to room light on a

desk top for about one day had an average background of 147 picocoulombs~

Data from earlier experiments with bare TL blocks show that this enhanced

response from ultraviolet exposures must come from the thermoluminescence

of the tape adhesive. In another experiment, cards were exposed to desk

top fluorescent room light for periods of one-half to 4-1/2 hours in half-

hour intervals. The average background'readings varied from 62 picocou-

lombs for the half-hour exposure to 80 picocoulombs for the 4-112 hours

exposure. These results were somewhat random ~ . n d , when compared to the

results of the previous study, indicate that the thermoluminescent response

of the adhesive is a slowly varying function.of ultraviolet exposure

time .

11. BETA AND PHOTON DOSIMETRY

A. Theory. and ~ e s c r ' i ~ t i o n

Lithium-7 f l u o r i d e c r y s t a l s a r e thermal luminescent ( i . e . , they

have cen te r s which can t r a p charge c a r r i e r s crea ted b y ' t h e passage of an . . .

i on iz ing p a r t i c l e without permi t t ing recombination). This property de-

l a y s t h e luminescence accompanying t h e recombination of e l e c t r o n s and holes . . .

i n t h e r a d i a t i o n recombination cen te r s . The time of delay is a funct ion

of temperature. Another way o f , l o o k i n g a t t h e LiF c r y s t a l i s as an energy '

i n t e g r a t i n g device t h a t can s t o r e energy imparted by ion iz ing r a d i a t i o n

and then r e l e a s e t h a t energy a s o p t i c a l energy when t h e c r y s t a l i s heated

. . t o t h e proper temperature.

The manner i l lwh ich photons deposi t energy i n a TL c r y s t a l i s

through t h e production o f energet ic secondary e lec t rons and it i s t h e

i n t e r a c t i o n of t h e s e secondary p a r t i c l e s which account predominantly f o r

t h e imparting of energy t o t h e TL mate r i a l . The c lose r e l a t i o n s h i p of

. t h e e f f e c t i v e atomic numbers and assoc ia ted c ross sec t ions of LiF and

. .

s o f t t i s s u e i s t h e key t o c lose t i s s u e equivalence o f LiF.

The multipurpose dosimeter card has two 7 ~ i ~ TL blocks t h a t a r e . .

i s o t o p i c a l l y enriched i n ' ~ i t b 99.993 percent f o r b e t a and photon dosi-

metry. The pos i t ions of t h e two blocks ( # 1 and #2) i n t h e dosimeter card . .

a r e shown i n Figure 1. When t h e dosimeter card i s i n s e r t e d . i n t o t h e holder , 7 '

a snug f r i c t i o n f i t i s obtained and t h e block i n pos i t ion #1 i s loca ted i n

t h e open, wini lnw where it i s I'l1l;ered by only , i t s associa ted Teflon TFE

t a p e and t h e s e c u r i t y c r e d e n t i a l . .The TLD i n pos i t ion #2 i s s h i e 1 d e d . b ~

an a d d i t i o n a l 0.089 cm of p l a s t i c and 0.064 cm of aluminum. The two blocks

b - ' . . . . . . . ..

. \ . . . . . u . '

. . . . -9- .

. . . .

serve a s a simple two-element photon-beta p a r t i c l e spectrometer . .The 0.089

c m block th ickness was chosen t o provide adequate s e n s i t i v i t y and t o elim-

i n a t e breakage problems encountered with t h i n n e r blocks. The use of t h e

t h i c k e r block makes necessary a compromise on t h e i n t e r p r e t a t i o n of t h e .

response of block #1 ( t h e "open window"). This w i l l be explained i n more

. _ d e t a i l l a t e r i n t h i s sec t ion . . .

The thermo$uminescent response of block #2 i s i n t e r p r e t e d a s

pene t ra t ing dose and i t s sh ie ld ,was designed t o correspond t o one cen t i -

meter of soft t i s s u e f o r photon energies from 1 0 keV t o 10 MeV a s shown

i n Figure 4. F o r b e t a dosimetry, t h i s s h i e l d i s about 365 mg/cm2 t h i c k .

I f t h e photomul t ip l ier tube cur ren t i s in teg ra ted dur ing t h e

r eadou t 'p rocess , then t h e dose , i n t e r p r e t a t i o n i s accomplished with t h e

following equations:

z Penet ra t ing dose = - m a d s

kl

R1 - k2R2 Derma dose = pene t ra t ing dose + L m a d s ( 2 )

where R and R2 a r e t h e n e t in teg ra ted phototube cur ren t s from t h e # 1 and 1

#2 T'L 'blocks and k k and k ' a r e t h e c a l i b r a t i o n constants determined by 1, 2 3

exposures t o s e l e c t e d sources.

The sources used a r e . s e l e c t e d t o provide s p e c t r a of photon and

b e t a r a d i a t i o n which arc reprcocnta t ive of r a d i a t i o n f i e l d s a t var ious

Hanford work' a r e a s ,

B. Photon Energy Resp

The photon energy response .of t h e shie lded TL blocks i s important.

The energy response function of # 1 TL block wi th in t h e Teflon envelope and

shielded by 0.076 cm of p l a s t i c i s e s s e n t i a l l y f l a t from 100 k e ~ ' t o 1 .25

MeV, 'as shown i n Figure 5. The response increases below 100 .keV and

reaches a maximum at about 35 keV. A t t h i s po in t , t h e r.esponse i s about

140 percent of t h e 1:25 MeV response. A t about 16 keV, t h e response i s

again equivalent t o t h e response a t 1 .25 MeV end then it drops sharply t o

0 . 1 r e l a t i v e t o 1.25 MeV when t h e phot.on energy i s 8 keV.

Several f i l t e r system designs were s tud ied f o r poss ib le use i n .

t h e dosimeter badge t o provide a photon response propor t ional t o t h e one I

centimeter depth dose i n t i s s u e . The f i l t e r sys teu chosen was composed

of 0.178 cm of p l a s t i c plus 0.064 cm of aluminum. Badges were exposed t o

k-fluorescent x rays , f i l t e r e d x r a y s , and gamma rays t o experimental lx .

determine t h e response of t h i s f i l t e r -TL block system. Exposures were

made a t 16, 23, 34, 43, 58, 78, 100, 170, 662, 880 and 1250 keV e f f e c t i v e .

The response data a r e shown i n Figure 4 . A t 16 keV, t h e r e l a t i v e response

of t h e TL block shie lded by t h i s f i l t e r system . is about 35 percent of t h a t

a t 1.25 MeV. About t h e same f r a c t i o n of dose from 16 keV photons w i l l

penet ra te one centimeter of t i s s u e . Above 16 keV, t h e response of t h e

f i l t e r e d TL block system increases and reaches a peak a t 43 keV, which i s

about 135 percent of t h e response of t h e syctcm to 1.25 MeV. The penetra-

t i n g dose evaluat ion follows t h e ca lcu la ted one centime.l;er t i s s u e dose re-

sponse qu i t e we l l . There i s a small region aroirnd 40 keV where t h e TL re - '

sponse i s g r e a t e r than t h a t of t i s s u e ; t h i s makes t h e i n t e r p r e t a t i o n i n a

. .

mixed energy f i e l d s l i g h t l y conservative. It. should be pointed out t h a t

t h e penet ra t ing dose a s i n t e r p r e t & by t h i s f i l t e r system w i l l be some-

what higher than t h e penet ra t ing dose i n t e r p r e t e d from t h e present Hanford

f i lm badge which uses a 0.050 cm t h i c k tantalum f i l t e r system. This i s .

espec ia l ly t r u e i n mixed photon f i e l d s where photons with energies between

16 and 60 keV a r e present . An a d d i t i o n a l advantage of t h e TL badge i s i t s . .

f l a t response t o higb energy photons (> 2 M ~ V ) where p a i r production i n

t h e f i l m and tantalum f i l t e r o f , t h e Hanford f i l m badge requ i res a response

cor rec t ion when t h e high energy component of t h e photon f i e l d becomes

s i g n i f i c a n t .

C . Angular Dis t r ibu t ion Studies

A v a r i e t y of labora tory s t u d i e s were conducted t o determine ex-

perimental ly t h e beta-photon response of t h e TLD badge. One s e r i e s of . .

s t u d i e s was conducted using t h e photons from a 2 5 2 ~ f source Lnd a Remab

phantom f i l l e d with t i ssue-equivalent f l u i d . The phantom was placed hor i -

zon ta l ly on a four-foot high wooden t a b l e and t h e source was a t tached t o a

r i n g s tand d i r e c t l y above t h e ches t of t h e phantom. Badges were taped

around t h e phantom d i r e c t l y below t h e source, as s h ~ w n i n Figure 6. The

source was 71 centimeters from t h e ches t of t h e phantom. The net response

of badges i n symmetrical pos i t ions were averaged. The re'sponse of t h e

' TLDs i n t h i s arrangement depends only on t h e number of i n t e r a c t i o n s occur-

r i n g i n t h e TLD from any d i r e c t i o n . The response i s , the re fo re , dependent

on source-detector d i s t ance , a t t enua t ion , angular dependence, and s c a t t e r -

ing geometry. Ignoring cor rec t ions f o r these f a c t o r s , t h e g r e a t e s t response

i s on t h e f r o n t center of t h e ches t . A l l of t h e s e f a c t o r s become s i g n i f i -

cant a t t h e pocket and s i d e pos i t ions . The sh ie ld ing of t h e phantom and

t h e source-detector d i s t ance become.the g r e a t e s t f a c t o r s i n t h e reduction

. of t h e photon response f o r badges pos i t ion on t h e back o f . t h e phantom.

A s imi la r experimental procedure was used t o study t h e angular

. 60 v a r i a t i o n i n response of t h e TLD badge t o r a d i a t i o n from a Co source

placed twenty centimeters from t h e ches t of t h e phantom (Figure 7 ) . This

study was concerned only with t h e penet ra t ing photon responsk of t h e badge

and included angles up t o 90' from normal both r i g h t and l e f t of t h e ten-

t e r of t h e ches t . The TL block used f o r pene t ra t ing dosimetry i s loca ted

on t h e r i g h t s ide of t h e card and t h e response should vary depending on

t h e source-detector d i s t ance , t h e e f f e c t i v e s h i e l d th ickness of t h e f i l t e r

system a s a funct ion of angle , and s c a t t e r i n g geometry of t h e source and

phantom. The source-detector d i s t ance f a c t o r and t h e reduction i n . t h e . .

e f f e c t i v e s h i e l d th ickness make t h e response g r e a t e r when t h e source i s

t o t h e r i g h t of cen te r th.an a t 0 degrees. For angles near 90' t o t h e

r i g h t , t h e e f f e c t i v e sh5elding of p l a s t i c i n t h e card and holder i s

s l i g h t l y l a r g e r than t h e sh ie ld ing of t h e f i l t e r system and t h e response

drops o f f . When the svurce i s t o t h e l e f t of c e n t e r , t h e source-detector

d is tance and t h e e f f e c t i v e sh ie ld ing of t h e badge and f i l t e r system con-

t i n u e t o increase through 90'. The l o s s of response on t h e r i g h t s i d e is I

about 10 percent and t h e l o s s on t h e l e f t . s i d e i s about 40 perccnt a t 90'.

D . Mixed Radiation Exposures

A.dosimeter under f i e l d condi t ions i s very seldom exposed t o a

s i n g l e monoenergetic source of r a d i a t i o n . . I t i s imperat ive, t h e r e f o r e ,

t h a t t h e dosimeter be capable of accura te dose i n t e r p r e t a t i o n of t h e v a r i - .

ous kinds and s p e c t r a of r a d i a t i o n t o which it may be exposed. To study

. . t h i s proper ty of t h e TLD badge, eleven combinations of 1 6 - k e ~ x-ray,

uranium b e t a , radiwn'gamma and PuF,, exposures were arranged a n d two TLD

badges were exposed t o each combination. It i s evident from t h e da ta i n

Table I1 t h a t t h e TLPbadge does meet t h e c r i t e r i a described above. I n

t h i s t a b l e ; P s tands f o r pene t ra t ing dose and D f o r derma dose. The dose

given i n each ins tance was i n t e r p r e t e d from t h e known exposure.

When 9 0 ~ r r a d i a t i o n is used f o r t h e drrma dose c a l i b r a t i o n of

t h e TLD badge, t h e response i s about 40 percent lower than t h e response

t o radium gamma c a l i b r a t i o n and about 50 'percent higher than t h e response

t o uranium b e t a c a l i b r a t i o n . ~ o w e k e r , was found t o be a good i n t e r -

mediate c a l i b r a t i o n f o r mixed f i e l d s . The photon-beta con t r ibu t ions f o r

a l l Hanford sources u f exposure tend t o average out a r ~ d i n t e r p r e t w e l l

with t h e 9 0 ~ r c a l i b r a t i o n . I n o ther words, t h e TLD system w i l l t end t o

provide an underestimate of a pure low energy b e t a exposure.

E. Specia l F ie ld Studies

A number of s p e c i a l s t u d i e s were conducted at several work loca-

t i o n s around t h e Hanford p lan t t o observe t h e response of t h e beta-photon

TLD badge and t o make comparisons wi th instruments and t h e present f i l m do-

s imeter . Resul ts were evaluated a s pene t ra t ing and derma dose us ing t h e

MIXED DOSE COMPARISONS ( m a d s )

- -Dose Given TLD .

c a l i b r a t i o n s previously descr ibed. The TLD badge y ie lded genera l ly con-

s i s t e n t r e s u l t s f o r a l l of t h e var ious exposures. The f i l m genera l ly

agreed with t h e TLD badges and instruments except i n those cases where

mixed f i e l d s of x r a y s , a n d bc tas ,were encountered o r photon exposures . I

exceeded t h e l i m i t s of t h e f i lm.

~ n o t h e r f i e l d study was conducted by p lac ing TLD badges on Han-

fo rd personnel along with t h e i r r egu la r f i l m badges a n d , i n somc cases ,

penc i l dosimeters . A l l of t h e c h a r a c t e r i s t i c s of t h e badges thus f a r de-

sc r ibed were observed. . The t r end f o r t h e TLD t o show more pene t ra t ing

dose than t h e f i l m badge i s ' g r a p h i c a l l y displayed i n Figure 8. A s i m i l a r

graph of comparisons of derma dose a r e shown i n Figure 9. Several com-

parisons with Stephens self-reading penc i l s worn by reac to r personnel

showed very good c o r r e l a t i o n with TLD badges worn a t t h e same time.

Some concern has been voiced about t h e p l a s t i c s e c u r i t y creden-

t i a l sh ie ld ing of t h e TLD i n pos i t ion #1 with respect t o be ta s e n s i t i v i t y .

Subsequent s.tudies ind ica te t h a t a hole i n t h e cr.edentia1 would increase

t h e b e t a sens i t iv i ty 'o f t h e TLD about 25 percent and reduce ' t he lower li-

m i t of' de tec t ion of uranium betas from about 50 m a d s t o 25 m a d s . Expo-

sures of these "open window" badges t o mixed r a d i a t i o n a s described above

was repeated and t h e r e s u l t s showed an i n s i g n i f i c a n t increase i n derma

dose i n t e r p r e t a t i o n compared t o t h e badges with normal s e c u r i t y

c reden t i a l s .

For beta-photon dosimetry, t h e reproduc ib i l i ty (p rec i s ion) can

be maintained wi th in - + 5 percent a t t h e 67 percent confidence l e v e l on

doses g rea te r than 300 m a d , wi th in - + . I 5 percent a t t h e 67 percent conf i -

dence l e v e l on doses down t o 100 m a d , and - + 50 percent a t t h e 67 percent

confidence l e v e l with doses o f about 20 m a d . We consider t h e low l e v e l

de tec t ion l i m i t s t o be 20 m a d of penet ra t ing . r a d i a t i o n and 10 m a d s of

nsril-penetrating r a d i a t i o n . . .

111. NEUTRON DOSIhETRY

A. Theory and Descript ion

The slowing down of neutrons i n a human body i s due mostly t o

e l a s t i c s c a t t e r i n g with hydrogen nuc le i and it i s t h e subsequent r e c o i l

protons which a r e responsible f o r most of t h e neutron dose del ivered t o

t h e body. For neutron energies below 10 MeV, t h e e l a s t i c s c a t t e r i n g i s

near ly i s o t r o p i c i n t h e labora tory system and, because of t h e amount of

hydrogenous m a t e r i a l i n t h e body, t h e leakage spectrum of neutrons from

t h e body i s p r imar i ly a thermal spectrum. By monitoring t h i s leakage

spectrum 'of neutrons, a f i r s t order measurement can be made of t h e f a s t

neutron dose del ivered t o t h e body.

The Hanford multipurpose neutron dosimeter has t h r e e LiF blocks.

6 Two of t h e blocks a r e i s o t o p i c a l l y enriched t o 95 percent L i and t h e

7 t h i r d block i s enriched t o 99.993 p e r c e n t Li . The pos i t ions o f ' t h e

t h r e e elements i n t h e dosimeter card a r e shown i n Figure 1. Pos i t ions #3

6 7 and #4 a r e LiF blocks and pos i t ion # 5 i s t h e LiF block. Thermal neu-

t r o n s deposi t energy i n t h e b ~ i ~ block by t h e n u c l e a r r e a c t i o n

6 1 4 3 Li + n + He + 3~ + 4.78 MeV 0 2 1

The a lpha and t r i t o n p a r t i c l e s share t h e excess energy from t h i s r e a c t i o n . .

'and deposi t most of t h i s energy i n t h e IJZ c r y s t a l s s ince t h e dimensions

' o f t h e TL blocks a r e l a r g e compared t o t h e range of t h e s e p a r t i c l e s i n

LiF.

6 The bare LiF block responds equal ly we l l t o backscat tered neu-

t r o n s from t h e body as we l l a s t o t h e inc iden t neutron cur ren t . The i n c i -

dent neu'l;ron current can be thought of a s cons i s t ing of j u s t slow and f a s t

6 ncuti-ons, $ and m f , r e spec t ive ly ( s e e Figure 10). The ~ i ( n , a ) c ross set- s

t i o n ( see Figure 11) i s about 1000 barns f o r thermal neutrons whereas it

6 i s only 0 .3 barns f o r a 1 . 0 MeV neutron. Therefore, t h e LiF TL block i s

a r e l a t i v e l y poor d e t e c t o r f o r f a s t neut rons 'and f o r p r a c t i c a l a p p l i c a t i o n s ,

t h e c o n t r i b u t i o n t o i t s thermoluminescence due t o f a s t neutron cap tu re can

b be ignored. The LiF TL b lock i n p o s i t i o n #4 i s s h i e l d e d from i n c i d e n t .

slow neutrons by p l ac ing 0 .051 cm of cadmium i n f r o n t of it. The cadmium

t o t a l l y absorbs a l l of t h e i n c i d e n t neut ron of e n e r g i e s below 0.4 eV. This

cadmium abso rp t ion i s by a n , ( n , y ) r e a c t i o n and' some o f t h e r e s u l t i n g pho-

t o n s d e p o s i t energy i n t h e TL b lock . I f t h e i n c i d e n t slow neut ron were

allowed t o i n t e r a c t i n . t h e TL b lock , it would d e p o s i t 4.78 MeV of energy;

whcreas i f ' it i s absorbed i n cadmium and t h e cadmium photons i n t e r a c t i n

t h e TL m a t e r i a l , it can depos i t only a few eV o f knergy i n t h e b lock due

t o t h e s m a l l mass and low atomic number of t h e TL m a t e r i a l .

The backsca t t e r ed neutrons t h a t a r e c a p t y e d i n t h e 6LiF b locks

a r e s c a t t e r e d slow neut ron ( 4 ' ) and t i s s u e moderated f a s t neut rons ( @'). S f

The magnitude of backsca t t e r ed neut ron c u r r e n t d e n s i t y pe r u n i t i n c i d e n t

f a s t f l u x has been c a l c u l a t e d by P. S . Nagarajan and D . Krishnan ( l o ) and

exper imenta l ly measured by J. A. Dennsi, J. W . Smith, and S. J. Boot. ( 1 1

' I f we ignore photon response , t h e above d i s c u s s i o n can b e summarized by

w r i t i n g equat ions f o r t h e r e l a t i v e response of TL b locks #3 and #4.

wherc R aiid R a r e t h e r e l a t i v e thermoluminescent response of TL b locks 3

. . 4 6 3 #3 and 84, n i s a p r o p o r t i o n a l i t y c o n s t a n t , and U ( E ) i s t h e ~ i ( n , a ) H

c r o s s s ec t ion . . The d i f f e r e n c e between R and R 4 no(^)+^] can b e r e l a t e d 3

t o t h e i n c i d e n t thermal neutron dose

where k i s a c a l i b r a t i o n constant . By exposing t h e badge ' to a source of 4 thermal neutrons, +f and I$' a r e zero s o t h a t Equation (3) and ( 4 ) would

f '

be

The r a t i o of b+ckscat tered thermal t o i icident thermal neutrons .can be

defined as a cons tant :

I f we s u b t r a c t t h a t por t ion of t h e backscat tered neutrons which a r e due t o

inc ident slow neutron ( k + ) from t h e bracketed term i n Equation ( 4 ) , then 5 s

t h e response of Rq i s propor t ional t o only +' T h i s c a n then be r e l a t e d f '

t o f a s t neutron dose.

. . 6 The LiF blocks are a l s o photon s e n s i t i v e -and it i s imprac t i ca l

t o adequately s h i e l d them f r o m ' a l l photon r a d i a t i o n . Therefore, a t h i r d

7 block of LiF enriched TL m a t e r i a l ( i n s e n s i t i v e t o neut rons) i s placed i n

pos i t ion #5 of t h e dosimeter card and . sh ie lded f r o n t and back by 0.102 cm

of t i n t o prevent b e t a p a r t i c l e s and low energy photons from i n t e r a c t i n g

i n t h e TL blocks and poss ib ly causing s t a t i s t i c a l problems i n low neutron

dose i n t e r ~ r e t , a . ~ i . o n s . The TL Llvck i n pos i t ion #3 i s s i m i l a r l y sh ie lded

and t h e block i n p o s i t i o n #h .has 0.102 cm of t i n on t h e back and 0.051 cm

of t i n on t h e f r o n t between t h e cadmium and t h e block. This arrangement

makes a l l t h r e e blocks photon equivalent and he lps ' r educe t h e photon con-

t r i b u t i o n f rom' the a c t i v a t e d cadmium i n p o s i t i o n #4. The f a s t neutron

dose i s then i n t e r p r e t e d using t h e following equation: .

R 4 - k6R5 - k 5 ( ~ g - R ~ ) Fas t neutron Dose = k m a d s ( 9 )

7

where k i s a correcBion f a c t o r f o r t h e d i f fe rence i n photon s e n s i t i v i t y 6 7 between t h e 'LiF and LiF TL blocks , and k i s 5 c a l i b r a t i o n constant .

7 The constant k i s evaluated by solv ing Equation ( 5 ) a f t e r 4

known exposures of t h e badge t o thermal neutrpns i n t h e Hanford sigma

- p i l e . The constant k i s evaluated by solv ing Equation (8 ) a f t e r s e t t i n g 5

t h e f a s t neutron dose equal t o zero and evaluat ing t h e resyonses f o r t h e

same exposures a s described above f o r evaluat ing k The constant k i s 4 ' 6

evaluated by solving

a f t e r exposing t h e badges t o a pene t ra t ing photon ca l i .bra t ion source. For

f a s t neutron c a l i b r a t i o n , t h e badges a r e a t tached t o a phsn-

tom. The constant k i s then evaluated by solv ing Equation ( 9 ) a f t e r ex- 7

posing t h e badges t o neutrons from a plutonium f l u o r i d e c a l i b r a t i o n source.

Most of t h e neutron exposures a t Hanford a r e due t o neutrons

which have a broad energy d i s t r i b u t i o n . Because of t h i s s p e c t r a l d i s t r i -

but ion , t h e neutron badge w i l l t end t o average t h e dose response. Table

I11 i l l u s t r a t e s t h i s averaging process ' on t h e two d i s s i m i l a r neutron

Energy I n t e r v a l MeV

-20-

TABLE 11'1 .

MODERATED FISSION SOURCE

Dose per Energy I n t e r v a l

Re la t ive D i f f e r e n t i a l

Response

BARE FISSION SOURCE

Percent Response

s p e c t r a ( I 2 ) shown i n Figure 12 and ~ i & e 13. This shows t h a t t h e r e l a t i v e

response of t h e TL neutron badge t o an unmoderated f i s s i o n spectrum w i l l be

.99 compared t o a response of 2.45 f o r a heavi ly moderated f i s s i o n spectrum.

' I t i s f e l t t h a t t h e s e s p e c t r a r ep resen t t h e extremes of neutron s p e c t r a

found a t Hanford. . .

S p e c t r a l consi 'derations and assoc ia ted q u a l i t y f a c t o r s were s tu -

d ied a t a v a r i e t y of work loca t ions a t Hanford and t h e s e da ta a r e shown i n

Table I V . The measurements were made with a - t i s s u e equivalent propor t ional

.counter (TEPC ) which measures absorbed dose d i r e c t l y . . An average q u a l t i y

f a c t o r (&F) can a l s o be obtained from t h e TEPC d a t a . These da ta can then

be compared f o r v a r i a t i o n s i n many of t h e neutron s p e c t r a a t Hanford. The

range i s from 8 .5 foc a bare 2 5 2 ~ f , source t o 12 .0 f o r a heav i ly sh ie lded

plutonium s to rage v a u l t . The average of a l l t h e s e @s i s 10 .l. The PuFh

. - source used f o r f a s t neutron c a l i b r a t i o n has a Ql? .of 10 .0 . The accuracy

of t h e s e measurements i s about + 1 &F u n i t s o it would seem t h a t t h e use - of PuF a s a f a s t neutron c a l i b r a t i o n source i s j u s t i f i e d .

4

QUALITY FACTOR MEASUREMENTS

Run

PuAl Fuel P l a t e s

234-5 Building

1 0 5 - ~ ~ Building

Top #23 Front Face

308 Building

Room 208 Corr #7 Vent Room (18" s h i e l d i n g ) Room C

2 5 2 ~ f are) PuF4 ( C a l i b )

Quali ty Factor ( TEPC )

AVERAGE

B. Fading and Annealing

The genera l fading and.anneal ing procedures used on t h e Hanford

TLD badge have been discussed i n d e t a i l elsewhere i n t h i s r e p o r t . ~ o w e i e r ,

a few s p e c i f i c items need t o be e labora ted upon here . The method of depo-

s i t i o n of energy due t o neutrons i s d i f f e r e n t from t h a t of b e t a p a r t i c l e s

and photons a s described previously. A s a r e s u l t , deeper t r a p s i n t h e TL

m a t e r i a l a r e act ivatGd and somewhat higher temperatures a r e needed t o com-

p l e t e l y empty them. It i s genera l ly agreed t h a t 300°C. i s adequate t o

readout neutron induced t r a p s . But, because o f t h e heat t r a n s f e r through

t h e Teflon t a p e holding t h e TL blocks , we have found t h a t 300°C f o r t h e

h e a t e r i s a minimum and 310°C i s more r e l i a b l e . A l l o the r a spec t s of

fading and annealing f o r TL m a t e r i a l s are appl icable .

Neutron Energy Response

The TL neutron dosimeter must be photon cor rec ted and, a s s t a t e d

above, a l l t h r e e blocks a r e sh ie lded t o provide photon equivalence. The

sh ie ld ing does not allow passage of photons with energies l e s s than about

60 keV and t h e blocks have a ' f l a t response f o r photons g r e a t e r than 100 -

keV, a s shown i n Figurc 1 4 . The neutron energy response was measured using

monoencrgetic neutrons from a Van de Graaff acce le ra to r . Measurements were

made from 100 keV t o 5 MeV and t h e r e s u l t s a i e shown i n Figure 15.

D . E f fec t of Dosimeter Wearing Pos i t ion

An experiment was made t o determine t h e e f f e c t i v e cen te r of t h e

TL phantom system f o r f a s t neutron dose i n t e r p r e t a t i o n s . I f we assume t h e

center of t h e de tec to r system ( i . e . , badge plus phantom) i s not a t t h e TL

2 p o s i t i o n , then R = ~ / ( x + a ) , where R i s t h e net response of t h e TLD t o

f a s t neutrons, A is t h e p ropor t iona l i ty constant , x i s t h e d i s t ance from '

t h e surface of t h e phantom t o a point neutron source and a i s t h e d i s t ance

from t h e surface of t h e phantom t o t h e e f f e c t i v e center of t h e de tec t ion

2 /2 -1 /2 system. I n l i n e a r form, x = (A/R) - a . I f x i s p l o t t e d versus R Y

a i s t h e i n t e r c e p t . .A 2 5 2 ~ f source was used and d a t a were obtained f o r

s i x values of x . The in te rcep t was a t - 4.5 cm. This means t h e e f f e c t i v e

center of t h e de tec t ion system i s 4 .5 cm deep from t h e surface of t h e phan-

tom. This e f f e c t i v e center i s only unique f o r a bare f i s s i o n spectrum of

neutrons ( i . e . , t h e e f f e c t i v e de tec t ion cen te r i s a l i n e a r funct ion of t h e

neutron energy). This r e s u l t confirms previous experiments with var ious

moderator th icknesses versus to ta1 , response t o f a s t neutrons.

, When t h e TLD neutron badge i s worn by a person, t h e badge i s

very seldom i n contact with t h e body. Since t h e f a s t neutron response de-

pends on backscat tered neutrons, a study of t h e r e l a t i o n s h i p between re -

' 1 sponse and badge-to-phantom dis tance was made. Se t s of t h r e e badges each

were posi t ioned i n f r o n t of a ches t phantom and exposed t o t h e standard

PuF calj.bra.tion sourcc. Each s e t was posi t ioned a t a d i f f e r e n t d i s t ance 4 ' \

from t h e surface of t h e phantom. In t h i s s tudy, t h e phantom was s e t a t

b

35 crn from t h e source and, the re fo re , t h e badges were a t various d is tances

from t h e source. The r e s u l t s a r e shown i n Figure 16. The response, when

t h e badge i s c lose t o t h e su r face , i s . s m a l l e r than one would expect com-

pared t o t h e response a t 2 cm due t o t h e e f f e c t of t h e r e l a t i v e l y l a r g e . .

cadmium s h i e l d i n t h e badge; The response increases out t o about one

centimeter a s t h e e f f e c t i v e s h i e l d s i z e decreases. ' A t 3-6 cm, t h e response . .

drops ' o f f s i m i l a r t o an R-' curve. A datum point from 0.56 MeV neutrons . .

produced by our Van de Graaff a c c e l e r a t o r and. one from a Harwell s tudy (11)

us ing 0.120 MeV neutrons f a l l on t h i s curve.

To b e t t e r understand t h e response of t h e badge i n d i f f e r e n t wear-

ing p o s i t i o n s on a hunan, badges were taped over t h e b r e a s t bdne, each

s h i r t pocket p o s i t i o n , each s i d e , and ac ross t h e back of a Remab phantom,

as shown i n Figure 1 7 . The response of t h e badges i n symmetric p o s i t i o n s

r e l a t i v e t o t h e neutron source were averaged and correc ted f o r background.

For t h i s geometry, t h e slow neutron cur ren t (energies below cadmium cut- .

. .

o f f ) inc iden t on t h e phantoms i s symmetric with r e spec t t o t h e phantom .

and i s p r imar i ly due t o thermal iza t ion of neutrons i n t h e f l o o r and walls ,

of t h e room. The maximum f a s t ' n e u t r o n response i s a t t a i n e d when t h e badge

i s on t h e cen te r ches t p o s i t i o n of t h e phantom. The response a t t h e f r o n t '

pocket p o s i t i o n s i s down by a f a c t o r of about t h r e e because t h e a i r f i l l e d

lung c a v i t i e s of t h i s phantom cause a smal ler f r a c t i o n of neutrons t o be

, . thermalized and s c a t t e r e d back t o t h e badge. No attempt has been made t o .

c o r r e c t f o r t h e r a d i a l dependence of t h e neutron f luence f o r t h e d a t a

shown i n \his f i g u r e . . .

'

A s i m i l a r set-up was .used t o expose t h e badge t o neutrons of 4.5;

1 . 0 , and 0.35 MeV generated with t h e Van d.e Graaff a c c e l e r a t o r . Resu1l;s

a r e shown i n Figure 18 . Badges were taped a t various pos i t ions around t h e

phantom as. ind ica ted above. However, . the phantom used f o r t h e s e exposures

d id not have void c a v i t i e s t o r ep resen t t h e lungs.

A s i m i l a r experiment was used t o s tudy t h e neutron angular r e -

sponse of t h e badge. A 2 5 2 ~ f source was placed 22 cm from a phantom and

adjus ted through 90° of a r c a t 22-1/2' i n t e r v a l s . Two badges pos i t ioned

. a t t h e cen te r of t h e chest were exposed t o 81 m a d s of f a s t neutrons f o r

each -exposure. The r e s u l t s were averaged, correc ted and p l o t t e d i n Figure

19. The f a s t neutron response under these condi t ions depends p r imar i ly

on t h e s c a t t e r i n g geometry of t h e source and phantom. The response de-

creased by a f a c t o r of four a t 90' t o normal. The thermal neutron response

dropped off slowly through a l l angles . This would i n d i c a t e t h a t t h e r e i s

s c a t t e r i n g of thermal neutrons such t h a t t h e con t r ibu t ion t o t h e f ace of - t h e badge i s f a i r l y cons tant .

. Mixed Radiat ion and Specia l F i e l d Studies

A s ste.ted i n Section II.D., a dosimeter under f i e l d condi t ions

i s very seldom exposed t o a s i n g l e source of r a d i a t i o n . It is t h e r e f o r e

necessary t h a t t h e TLD badge be capable of accura te neutron dose in te rp re -

t a t i o n when exposed t o a v a r i e t y of d i f f e r e n t kinds of r a d i a t i o n . To

study t h i s proper ty , eleven combinations of 16 keV x-ray, uranium b e t a ,

radium gamma and PuFq neutron pxpnsurec wcre made using two TLD badges

f o r each comhination. These d a t a , shown i n Table V , show t h a t t h e mul t i -

purpose dosimeter provides reasonable dose i n t e r p r e t a t i o n f o r ' n e u t r o n s

.when mixed combinations of r a d i a t i o n s a r e p resen t .

Another s tudy was conducted by t ap ing TLD and NTA f i l m badges t o

two-gallon jugs f i l l e d wi th water and p lac ing t h e s e jugs i n work loca t ions

a t Hanford. Remmeter readings were made a t each l o c a t i o n . The TLD badge

TABLE V

MIXED DOSE COMPARISONS

Dose Given ( m a d )

Run 1 6 keV Ug PuF4 Ray -

TLD 'mrads

n n - f -

d e t e c t e d neutrons i n every l o c a t i o n where neutrons were shown t o e x i s t I

by t h e neut ron remmeter. The NTA f i l m f a i l e d t o do t h i s i n many c a s e s .

It w a s observed i n many cases t h a t t h e NTA f i lm ,was fogged and f a s t neu-

t r o n dose w a s uninterpretab1.e when t h e f i l m had been exposed t o moderate

doses of p e n e t r a t i n g and/or non-penetrat ing r a d i a t i o n . Seve ra l inc idences

of t h i s occurred wi th derma doses a s low as 400 mrads from plutonium

f u e l s . The mult ipurpose badge on t h e o t h e r hand, y i e l d e d i n t e r p r e t a b l e

f a s t neutron d a t a from badges i n d i c a t i n g derma doses a s high a s 3200 m a d .

C r i t i c a l i t y s t u d i e s desc r ibed below i n d i c a t e accu ra t e f a s t neutron i n t e r -

p r e t a t i o n s i n t h e presence of very h igh photon exposures . The lower l i m i t

df f a s t neut ron i n t e r p r e t a t i o n s i n h igh photon r a d i a t i o n f i e l d s i s a

ma t t e r of s t a t i s t i c s and should be about 10 mrads + 100 percent f o r f a s t - neut rons i n a mixed exposure w i t h about 3000 m a d s of photons wi th read-

i n g s t a t i s t i c s of - + 5 pe rcen t . Exposures of t h e badge t o plutonium f u e l

sources have been c o n s i s t e n t wi th dose measurements w i t h l a b o r a t o r y

ins t ruments . . .

The next s t e p was t o p l ace TLD badges on personnel i n t h e f i e l d

and compare neutron dose i n t e r p r e t a t i o n wi th t h e r e s u l t s from t h e i r - r e g u -

lar f i l m badge dos imeters . Again, t h e TLD badge was ve ry c o n s i s t e n t i n

responding t o neut rons . The r e s u l t s of t h e s e f i e l d t e s t s a r e shown i n

Table V I . The thermal neut ron dose i n t e r p r e t a t i o n f o r t h e two badge

systems i n d i c a t e d thermal, neutrons where they .were known t o e x i s t i n t h e

f i e l d , b u t t h e TLD d i d a more c o n s i s t e n t job of responding t o f a s t neu-

t rons . . A @ of 3 and 1 0 has b e e n used f o r thermal and f a s t neut ron r e - .

s u l t s , r e s p e c t i v e l y .

S t a t i s t i c a l a n a l y s i s of t h e d a t a i n d i c a t e s t h a t t h e TL neut ron

dosimeter car1 c o n s i s t e n t l y d e t e c t 0 . 5 m a d of thermal neut rons and 5 mrads

of f a s t neutrons w i t h i n t 50 percent under i d e a l cond i t i ons .

Exposures s imu la t ing a nuc lea r c r i t i c a l i t y acc iden t were conduc-

t e d a t t h e Heal th Physics Research Reactor at Oak Ridge Nat iona l Labora-

. t o r y . The HPRR i s a f a s t b u r s t r e a c t o r which can produce a h igh neut ron

and gamma dose i n a r e l a t i v e l y s h o r t t ime ( % 50 p s e c ) . Measurements were

made of t h r e e b u r s t s ; one wi th no s h i e l d i n g between t h e r e a c t o r and

dos imeters , one wi th 1 1 . 4 cm of l u c i t e between .the r e a c t o r and dos imeters ,

and one wi th about 5 cm of i r o n between t h e r e a c t o r and dos imeters . The

TABLEVI

NJZXJTRON RESULTS FROM FIELD STUDIES

Ehnployee . . Number

Slow Neutrons (mrem)

TLD Film - - 6 30

9 30

12 4 0 *

6 . . 3 0

. . 3 0

6 30

9 .50

Fas t Neutrons (mrem) I

TLD Film - - .

f a s t neutron dose r a t e a t t h e c l o s e s t pos i t ions ' t o t h e HPRR was a s high

6 as 9 x 1 0 rads per second. . The accompanying gamma exposure r a t e was

7 about 2 x 10 R. per second.

No non-penetrating r a d i a t i o n was observed f o r any of t h e b u r s t

exposures. Dosimeters were a t tached t o water b o t t l e s t o serve as phan-

toms and placed a t d i s t ances of 3, 4 , 5 ,6 , 9 and 15 meters from t h e

r e a c t o r f o r a l l t h r e e b u r s t s ,

No dose r a t e dependence was observed for ' any o f . t h e b u r s t r e - . .

s u l t s with t o t a l dose r a t e s a s high a s 111 x l o7 rad/sec . Both g m a

and neutron dose measurements vary as 1 / R 2 , where R i s t h e d i s t ance from

t h e r e a c t o r , f o r a l l t h r e e b u r s t s . The r e s u l t s a r e shown i n Table V I I

f o r t h e b u r s t wi th no sh ie ld ing . The raw d a t a from each b u r s t i n d i c a t e

t h e presence of a l a r g e f l u x of thermal neutrons. The thermal neutron

f l u x i s s o l a r g e t h a t t h e co r rec t ion k (R - R ) i n Equation ( 9 ) ' f o r 5 3 4

thermal neutron e f f e c t s determined i n t h e Hanford Standard P i l e i s not

acceptable. A l l r e s u l t s f o r f a s t neutron .dose were determined without

a thermal neutron cor rec t ion .

TABLE V I I

GAMMA AND FAST NEUTRON DOSE RESULTS

Burst #1 16 . .

. .. 7.7 x 1 0 F i s s ions

Bare Reactor

. Rela t ive I n t e r p r e t a t i o n Distance Gamma Exposure Fas t Neutron ( ~ e t e r s ) ( R ) D o s e ( r a d s ) Photon Neutron 1 / R 2

. . For a l l t h r e e b u r s t s , the'TLD behind t h e heavy t i n f i l t e r used

f o r gamma compensation i n the neutron dosimeter showed evidence of high

energy gamma r a d i a t i o n . Response behind the t i n f i l t e r was 20 percent

. or more above t h e response behind t h e aluminum f i l t e r . The f i l t e r s i n

t h e neutron s e c t i o n a r e ' a l l photon equivalent s o t h e high energy response

does not a f f e c t t h e neutron evaluat ion . No s a t u r a t i o n e f f e c t s such as

. ' occur i n f i l m were seen. No super- l inear r e s u l t s were observed because

t h e t o t a l doses were j u s t below t h e point where super - l inea r i ty begins .

For both b u r s t s with a d d i t i o n a l sh ie ld ing , t h e dose va r i ed a s

t h e inverse square of t h e d i s t ance from t h e r e a c t o r . No r a t e e f f e c t s

. were observed. For t h e l u c i t e s h i e l d , t h e measured neutron dose it t h r e e

, meters was 200 rads compared t o 128 rads calcula.led. This shows an over-

response t o neutrons i n a heavi ly moderated geometry a s ind ica ted e a r l i e r

i n t h e d iscuss ion on bare and moderated geometries. For t h e b u r s t , w i t h ;

about 5 cm of i r o n , t h e measured f a s t neutron dose was 290 rads compared

t o a caxculated 228 rad a t t h r e e meters from t h e r e a c t o r . In t h i s case ,

t h e dosimeter was about 27 percent h igher than t h e c a l c u l a t i o n .

6 I V . ANNEALING AND FADING OF LiF AND 7 ~ i ~

6 7 The use of LiF and LiF TL m a t e r i a 1 s . h personnel dosimetry

app l i ca t ions r equ i res a r a t h e r d e t a i l e d knowledge of t h e annealing and

fading p roper t i e s of t h e s e ma te r i a l s . This i s e s p e c i a l l y t r u e i f t h e

readout process i s t o be mechanized by permanently mounting and hea t ing

t h e TL mate r i a l s i n a t r ansparen t mate ' r ial of some kind. The only known

transparent materials able to withstand the necessary readout tempera-

ture ( 300-310'~ ) are several types of .Teflon tape. Unfortunately, no

plastic material or Teflon tape is presently available that can with-'

stand the accepted. annealing temperature for LiF (400'~)~ and until the

problems of annealing and fading of LiF were better understood, the de-

sign of a fully automated system was impractical.

The prelimjnary concepts of the Hanford Multipurpose Dosimeter

were conceived after the discovery in 1968 and 1969 that LiF could be

read out at the normal reader temperature and held for one month at room

temperature. This process would maintain a constant sensitivity of the

A. Theory

A number of investigators have studied the glow peak structure

, . . ofLi~(~".~) aid found several peak present depending on radiation expo-

. .

sure and previous annealing history. If LiF is conditioned before expo-

sure by running it through the standard readout cycle, the resultant glow

curve is as shown in Figure '20. The prominent low temperature peak j s

approximately 80°C andShas a i;uulll Lemperature half-life of a few hours.'

The other peaks have half-lives of six months or longer at room tempera-

ture. Some lower temperature peaks also exist but are not.shown because

they fade within a few minutes after exposure.

When the LiF is conditioned through the standard readout cycle

and then held for eight days before exposure to radiation, the glow peak

structure is much different even though the TLD is read out soon after

. .

t h e exposure ( see ~ i ~ u r e ' 21) . These e f f e c t s a r e similar t o those observed

<,

by Zimmerman , e t a 1 . , (13) although they used d i f f e r e n t annealing tempera-

t u r e s . Zimmerman s tud ied t h e behavior o f n a t u r a l LiF us ing annealing tem-

pera tures of 8 0 ' ~ and g r e a t e r with t h e annealing time varying from a few

minutes t o 48 hours. I n t h e s e s t u d i e s , t h e 80°c peak i s found t o gradu-

a l l y disappear a s t h e annealing time inc reases . The s t r u c t u r e of t h e high

temperature glow peaks a l s o changes with annealing time and temperature.

The f r a c t i o n of t h e t o t a l response due t o t h e higher temperature peak&

inc reases a s t h e annealing time inc reases even though t h e o v e r a l l s ens i - - t i v i t y decreases . We have found t h a t t h e e f f e c t of keeping t h e LiF a t

room temperature f o r one month i s somewhat s i m i l a r t o t h e e f f e c t of

' (14) annealing a t 8o0C for 40 hours. Harr is and Jackson have repor ted .

s i m i l a r r e s u l t s i n a very d e t a i l e d study of annealing procedures.

B. Experimental Resul ts

The f i r s t experiments which l e d t o t h e discovery of t h e room

temperature anneal were conducted as a f ad ing s tudy t o determine how wel l

LiF holds t h e trapped e l e c t r o n s a t room temperature and only coinciden-

t a l l y revealed a d d i t i o n a l annealing information. For t h i s fading s tudy,

7 a s e t of LiF blocks was read through a modified commercial reader and

held eleven days before a s e r i e s of &posures'was begun. Some of t h e

TLDs were given 500 mR of radium gamma exposure on t h e e leventh 'day and

then he ld f o r readout at var ious t imes up t o 45 days. These r e s u l t s a r e ' .

shown i n Table V I I I and glow curves i n Figures 22a and 22b. Each r e s u l t

i s t h e average of t h r e e TLD readings with t h e background sub t rac ted . The

TABLE V I I I

SHORT TERM FADING OF 7 ~ i ~

Rela t ive Se t - Day Exposed Day Readout Reading

TABLE I X . .

ROOM TEMPERATURE ANNEALING

Day Exposed After Reader Cycle Day Readout

14

el at i v e Reading

readings decrease about 20 percent i n t h e 45 days a f t e r exposure. From

t h e same s e t of TLDs, another group was exposed a t var ious times a f t e r

t h e o r i g i n a l eleven-day holding period and read out wi th in 24. hours.

These r e s u l t s which i n d i c a t e t h e e f f e c t of t h e room temperature anneal

sh0w.a decrease i n response of only about 10 percent over t h e 1 4 t o 35

day time i n t e r v a l from t h e s t a r t of t h e experiment. Again, t h e exposures

were made i n groups of t h r e e TLDs and t h e r e s u l t s given i n able I X a r e

t h e average of t h e t h r e e readings . The g l o ~ r curve s t r u c t u r e E ~ O W E a

r a t h e r d r a s t i c change from t h a t a t 1 4 days compared t o 35 days ( s e e .

Figure 22c and 22d). Af te r 1 4 days a t rooni temperature, t h e 8o0C peak

i s , s t i l l q u i t e prominent i n d i c a t i n g t h a t t h e s h a l l o l ~ e r t r a p s i t e s a r e

s t i l l ava i l ab le t o be populated. But, a f t e r 35 days, t h e r e i s e s s e n t i a l l y

no evidence of t h e 8o0C peak. It appears t h a t most of t h e e f f e c t of

annealing i s due t o a . r e s t r u c t u r i n g of t h e t r a p s . This e f f e c t i s not

r e a l l y fading though it does affec: t h e fading p r o p e r t i e s s ince t h e

dosimeters were not exposed u n t i l a r e l a t i v e l y s h o r t t ime before they , .

were read ou t .

The r e s u l t s of t h i s f i rs t study suggested a one-month holding

period a t room temperature between readout and exposure t o r a d i a t i o n and

t h e next experiment was s o designed. The study was designed t o cover a

three-month per iod of' t ime t o s imulate a q u a r t e r l y readout cycie of t h e

dosimeters bu t was l a t e r extended t o cover more than one yea r . With a

one-month holding per iod a t room temperature, t h e r e i s no s i g n i f i c a n t

80°C peak i n t h e glow curve even when t h e exposure i s made wi th in 24

hours of readout . This c h a r a c t e r i s t i c c a r r i e d through t h e f u l l year t h e

experiment was corlduc'ted. Tu f u r t h e r t e s t the anneal proced~ire , t h e

dosimeters chosen f o r t h e one-year experiment were s e l e c t e d from a group

of TLDs t h a t were previous ly read out over a two-month time span. This

simulated a mixture of previous readout h i s t o r i e s . They were then he ld

an a d d i t i o n a l m0nt.h before t h e exposures and readout began. The r e s u l t s .

of t h i s long-term study a r e shown i n Figure 23. A l e a s t squares f i t t o

t h e d a t a from day one t o day 371 yie lded a s lope of 6 t o 7 percent per

y e a r , which i s compatible with r e s u l t s repor ted i n t h e l i t e r a t u r e .

These room temperature annealing r e s u l t s were very encouraging

and were i n agreement wi th da ta published by Harr is and Jackson. ( 1 4 ) The

r e l a t i v e l y , small decrease i n response over a one-year time per iod l e d

d i r e c t l y t o t h e technique of enclosing t h e 7 ~ i ~ block i n a t h i n Teflon

t ape holder f o r convenient automatic processing.

Annealing s t u d i e s were conducted over a period of four months

7 with LiF blocks enclosed i n Teflon t a p e and mounted i n t h e dosimeter

card. The cards were exposed t o 320 mR radiun gamma and read out again

a t 250°C and h e l d one month a t room temperature. This cycle was repeated

four t imes wi th t e n cards each time. The average r e l a t i v e reading of t h e

t e n cards had a range of - + 6 percent with a v a r i a t i o n from 425 t o 478

reader u n i t s . The average of a l l four s e t s of readings was 453reader

u n i t s , a s shown i n Table X.

For a fading s tudy, some of the.same s e t o f dosimeter cards as

used f'or t h e annealing study were readout a t 3 1 0 ' ~ and held f'or one month

a t room temperature. On t h e f i r s t day a f t e r t h e one-month holding

per iod , a l l cards (35) were exposed t o 320 mH radium gamma r a d i a t i o n and

. p u t a s i d e t o be read out a t i n t e r v a l s f o r 3-1/2 months. The dosimeter

ONE-MONTH ANNEAL STUDIES

2 5 0 ' ~ Readout

One-month hold a t room temperature

Average Rela,l;i.ve

Date Exposure Reading - 12-8-70 320 m~ 443

1-11-71 320 mR 425 Average = 45.3

2-3-71 ' 320 mR 478

cards were read out i n groups of f i v e each time and ' the readings were correc-

t e d f o r background. The fading of these .dos imete r s over t h e 3-1/2 month

per iod was 1 2 percent a s determined by a l e a s t square f i t t o t h e d a t a shown

. . i n Table X I . ~ h ; amount of 'fading i s more than d e s i r a b l e but we f e e l t h a t

t h i s i s due t o reader f l u c t u a t i o n s r a t h e r than t h e TLDs themselves s i n c e t h e

long tcrm otudy yie lded a fading s i g ~ l i r i c a ~ l l y less severe.

Based on t h e work of Harr is and Jackson, . . (14) it appears poss ib le t o

maintain t h e s e n s i t i v i t y of t h e LiF by a s h o r t anneal process. a t higher tem-

pe ra tu re r a t h e r than t h e one-month anneal a t room temperature. A group of - dosimeter cards were read out a t 300°C, and divided i n t o two s e t s . One s e t

receive,d t h e standard one-month room temperature anneal; t h e o the r s e t re-

ceived a s h o r t anneal of 60°c f o r 24 hours and then f i v e days a t room

TABLE X I

FADING STUDY 7 Teflon enc losed L i

R e l a t i v e S e t - Exposed Re adout Exposure Reading

1 Day 1 Day 7 320 mR 4 48

2 .Day 1 Day 40 320 mR 424

4 Day 1 Day 60 320 mR 365

5 Day 1 Day 79, 320 mR 404

6 Day 1 Day 92 320 mR 382

7 Day 1 Day 107 320 mR 370

tempera ture . The dosimeter cards g iven t h i s s h o r t 60°c anneal were then' he ld

a t ' r oom temperature u n t i l t h e o t h e r s e t o f ca rds put through t h e one-month

room temperature annea l were ready . A f t e r one month, a l l t h e cards were ex-

posed t o 500 ln3 radium gamma, r a d i a t i o n . A l l dosimeter ca rds were r ead ou t on

t h e same day f o r comparison of sensi. t ivj , t ,y. This e n t i r e monthly cyc l e was

r epea t ed . Thc ca rds g iven t h e s h o r t annea l were about 1 5 percent l e s s s ens i -

t i v e t o t h e r a d i a t i o n than were those given t h e s t anda rd one-month annea l .

The r e s u l t s u s ing t h e s h o r t annea l were s t a t i s t i c a l l y more c o n s i s t e n t t h a n

were t h e r e s u l t s from ca rds annealed one month a t room tempera ture .

Another group of dosimeter ca rds w a s g iven t h e s h o r t annea l a f t e r

a 250°C readout and cyc led t h e same way each month f o r fou r months t o

determine how reproducible t h e readout was a f t e r exposure t o 320 mR

radium gamma. Ten dosimeter cards were used f o r t h e exposures a n d . t h r e e

cards were used t o determine background. A s shown i n Table X I I , except

f o r t h e second month, t h e r e s u l t s a r e q u i t e reproducible. The average

r e s u l t i s 367 with t h e second month included, and 357 without t h e second

month. The range of t h e r e s u l t s i s +11 and -5' percent with t h e da ta from

t h e second month included. Without t h e s e d a t a , t h e range i s +1 and -2

percent . The r e s u l t s shown f o r each month ake the average of t h e ten do-

s imeter readings minus t h e background. Thus, t h e shor t anneal process

seems t o g ive a cons i s t en t reading f o r s e v e r a l dosimeter cycles .

TABLE X I 1

EXPOSURE - ANNEALING STUDIES

Average Re la t ive

Month Exposure Reading

Average Result = 367 with Month #2

357 without Month #2

I n summary, e i t h e r t h e standard readout with a one-month room

temperature holding per iod o r a s tandard readout wi th a 24-hour ~ U O C oven

anneal with a five-day room temperature holding per iod w i l l adequately

annea l t h e mult ipurpose dosimeter c a r d . We recommend t h e l a t t e r proce-

dure because it w i l l a l low t h e dosimeter ca rds t o be r e tu rned t o f i e l d

use f a s t e r and t h e s t a t i s t i c a l v a r i a t i o n s appear t o be less . .

V . CONCLUSIONS .

A mult ipurpose thermoluminescent personnel dosimeter has been

t developed t o r e p l a c e *the Hanford f i l m badge. The dosimeter can be used

r epea t ed ly wi th proper annea l ing and main ta in a cons t an t s e n s i t i v i t y .

I ts photon energy response and s h i e l d i n g provide t h e p e n e t r a t i n g one

cent imeter t i s s u e depth dose and t o t a l derma dose qu i t e - a c c u r a t e l y over

a wide range of r a d i a t i o n sources and s p e c t r a found a t Hanford. The

c a l i b r a t i o n and i n t e r p r e t a t i o n procedures a r e s imple and do no t l eave

gaps o r unreasonable l i m i t s f o r any one k ind o r mixture of r a d i a t i o n .

'Ihe badge has a reasonable independence from body wearing p o s i t i o n and

7 angle of r a d i a t i o n inc idence . The LiF b locks a r e r e l a t i v e l y i n s e n s i t i v e

. . t o neutr.ons of any .energy s o no neut ron c o r r e c t i o n s a r e necessary f o r \

I beta-photon dose i n t e r p r e t a t i o n s .

Most of t h e n e i ~ t ~ r n n ~ x p o s 1 . r ~ ~ a t Hanford are due t o ncutrona

which have a broad energy distl-ibul;5on. Because of t h i s f a c t , t h e neut ron

dose i n t e r p r e t a t i o n obta ined from t h e mul t ipwpose badge a c c u r a t e l y r e -

f l e c t s personnel exposure, t o both ' f a s t and the rma l neut rons .

Because t h e TL b locks a r e r e a d and annealed whi le i n t h e p l a s t i c

dosimeter c a r d s , t h e s t anda rd annea l ing procedures u s ing 4 0 0 ~ ~ cannot be

used. O u r expe r imen ta l evidence and t h a t of o t h e r au tho r s show t h a t 300°C

.Ts an adequate pre-exposure annealing temperature for precision dosimetry.

. . At this temperature, we are able to adequately read out and pre-anneal the . .

blocks in the .same process. Data indicates that an additional 24-hour

6 0 ' ~ oven anneal with a five-day holding period at room temperature re-

stores the dosimeters to a uniform sensitivity. This process can be

r e repeated indefinitely.

V I . ACKNOWLEDGErnNTS

- The authors wish t o acknowledge t h e valuable a s s i s t ance

of'W. H. Bischoff , W. A . Crook, and D . L. ~ a g ~ a r d f o r t h e i r

work i n processing t h e t e n s of thousands of TL blocks associa-

t e d with t h e experiments, prototypes and f i n a l badges. The

authors a r e a l s o indebted t o J . P. Corley, K. R . Heid, R . L. - . .

Kathren, and H . V. Larson of t h e Battelle-Northwest Occupational

and Environmental Safe ty Department f o r t h e i r encouragement,

advice and support , and D . H., Denham and h i s s t a f f o f ' t h e

Radiological Ca l ib ra t ions Laboratory f o r t h e i r dependable

s e r v i c e and t e c h n i c a l a s s i s t a n c e .

VII. REFERENCES . -

1. Luminescence Dosimetry, Proceedings of International Conference on Luminescence Dosimetry, Stanford University, Stanford, California, June 21-23, 1965. CONF-650637, edited by Frank H. Attix (1967) .

2. Proceedings of the Second International conference' on Luminescence Dosimetry, Gatlinburg, Tennessee, September 23-26, 1968. CON~-680920 edited by J. A. Auxier, K. Becker and E, M. Robinson.

3. J. R. Cameron, N. Suntharalingam, and G. N. Kenney, Thermoluminescent Dosimetry, pp. 41, University of Wisconsin Press (1968).

4. G. W. R. Endres , "Thermoluminescence Dosimetry at anf ford ," Thermolu- minescence Dosimetry, p. 435-443, Proceedings of International Con- ference on Luminescence Dosimetry, stanford University, Stanford, California, June 21-23, 1965 , CONF-650637, edited .by F. H. Attix (1967).

5.' J. Cluchet and H. Joffre, "Applications of Thermoluminescence Dosimetry in Health physics ," CONF-650637, pp. 349-58 (1967).

6. L..F. Kocher, "A Personnel Dosimeter Filter System for Measuring Beta and Gamma Doses in Mixed Radiation Fields ,I1 HW-71746 (1962) .

7. R. L. Kathren, L. F. Kocher and'G. W. R. Endres, "Thermoluminescence Personnel Dosimetry at Hanford," BNWL-SA-2793.

8. C. L. Wingate, E. Tochilin and N. Goldstein, "~esponse of Lithium Fluoride to Neutrons and Charged Particles ,I1 ~0~~-650637, p. 427 ( 1 9 6 9 .

9. K. Ayyangas , A. R. Reddy, and G. L. Brownell, "some Studies on Ther- moluminescence from Lithium Fluoride and Other Materials Exposed to Ncutrono and Othcr Radiations ,I1 CONF-680320, p . 525 (1968). , ,

10. P. s'. Nagarajan and I>. Krishman, "~eutron Personnel Monitoring - Correction Factors and a Suggested Device for Measuring Intermediate Energy Neutrons ,I1 Health Physics 17, p. 323 (1969).

11. J. A. Dennis, J. W. Smith,. and S. J. Boot, "The Measurement, of the Dose Equivalent from Thermal and Intermediate-Energy Neutrons with. Personnel Dosimeters, I' AERE-R 5238 (1966) .

12. Committee Report, "~osimetry ~nvksti~ation of the Recuplex Criticality ~ccident," Health Physics 9, p. 757 (1963).

13. D . W . Zimrnerman, C . R . Rhyner and J. R . Cameron, "Thermal Annealing '

E f f e c t s on t h e Thermol~ninescence of L ~ F , " Heal th Physics 12, p. 525 (1966 1.

1 4 . A . M. H a r r i s and J. H . Jackson, "on t h e Low Temperature Annealing of TLD L ~ F , " Heal th Physics g, p. 162 ( 1 9 7 ~ ) . .

V I I I . FIGURE CAPTIONS .

.l. An exploded view of t h e Hanford ~ u l t i ~ u r ~ o s e Dosimeter Card.

2. View of dosimeter holder , s e c u r i t y c r e d e n t i a l and dosimeter card .

3. . Curve A i s the . r e sponse of two pieces of adhesive coated TFE Teflon

t a p e . Curve B i s t h e response of a sandwich cons i s t ing of one p iece

.. . of adhesive coated TFE t a p e , a TLD-700, and a piece of uncoated t a p e .

. curve C i s t h e same a s Curve B except exposed t o u.v. l i g h t .

4. One centimeter s h i e l d response compared t o . o n e centimeter t i s s u e .

5. The photon energy response funct ion f o r TLD block i n pos i t ion number

one of dosimeter card .

6 . Multipurpose TLD phantom d i s t r i b u t i o n - pene t ra t ing and derma dose -

60 7 . Multipurpose TLD angular response t o .Co gamma r a d i a t i o n . . .

8. Penet ra t ing dose comparison -mul t ipurpose TLD v s . f i l m b a d g e .

.9 . Derma dose comparison - multipurpose TLD v s . f i l m badge.

10 . Schematic r ep resen ta t ion of neutron exposure condi t ions .

6 11. The ~ i ( n , a ) c ross sec t ion a s a funct ion of neutron energy.

12. Neutron f l u x dens i ty and dose d i s t r i b u t i o n f o r an unmoderated c r i t i -

c a l i t y event .

13. Neutron f l u x dens i ty and dose d i s t r i b u t i o n f o r a heavi ly moderated

c r i t i c a l i t y event .

1 4 . The photon energy response funct ion f o r TLD blocks i n p o s i t i o n 3, 4 ,

and 5 of t h e dosimeter card .

15. Fas t neutron dose response a s . a function of neutron energy.

16. F a s t neutron respon'se as a f 'unction of t h e d i s t a n c e between t h e 'mult i -

purpose badge and t h e sur face- of a polye thylene phantom.

17 . F a s t and thermal neutron response as a func t ion of t h e p o s i t i o n of t h e

badge on a Remab phantom. . .

8 R e l a t i v e monoenergetic fast neutron response a s a func t ion of t h e

p o s i t i o n of t h e badge on a phantom. Data have been normalized t o

f r o n t c e n t e r p o s i t i o n .

19 . P a s t neutron response as a func t ion of i n c i d e n t neut ron angle .

20. Glow curve f o r 7 ~ i ~ a f t e r a s t anda rd readout c y c l e .

21. G l o w c&ve f o r 7 ~ i ~ a f t e r e ight-day hold ing pe r iod .

7 22. Glow curves f o r LiF a f t e r va r ious annea l ing and exposure cond i t i ons .

23. One-year f ad ing s tudy showing response of 7 ~ i ~ exposed a f t e r one-

month hold ing pe r iod a t room tempera ture . . .

FIGURE 1, AH EXPLODED VIEW OF THE HANFORD MULTIPURPOSE DOSIMETER CARD.

FIGURE 2. VIEW OF DOSIMETER HOLDER, SECURITY CREDENTIAL AND DOSIMETER CARD

FIGU

READER FMPERATURE, OC

RE 3. CURVE A IS THE RESPONSE OF TWO PIECES OF ADHESIVE COATED TFE TEFLON TAPE. CURVE B IS THE RESPONSE OF A SANDWICH CONSISTING OF ONE PIECE OF ADHESIVE COATED TFE TAPE, A TLD-700 AND A PIECE OF UNCOATED TAPE. CURVE C IS THE SAME AS CURVE B EXCEPT EXPOSED TO U.V. LIGHT.

-

0-0 - L-IIIII 0-0

0

I. 0. PHOTO t 0.051 PI t 0.064 Al t 0.051 PI TLD 700 RIBBON

o MEASURED RESPONSE

---- CALCULATED RESPONSE (1 cm TISSUE)

0.1

PHOTON ENERGY, MeV

FIGURE 4 . ONE CENTIMETER SHIELD RESPONSE COMPARED TO ONE CENTIMETER TISSUE.

0.1

PHOTON ENERGY, MeV

FIGURE 5. THE PHOTON ENERGY RESPONSE FUNCTION FOR TLD BLOCK I N P O S I T I O N NUMBER ONE OF DOSIMETER CARD.

- 0 PENETRATING DOSE

A DERMA DOSE

-

71 cm

-

-

I I 1 I I 0 FRONT CE ,NER

FRONT S l DE

S l D E B A C K S l D E

B A C K I

CENTER

FIGURE 6. MULTIPURPOSE TLD PHANTOM DISTRIBUTION - PENETRATING AND DERMA DOSE - 252cf.

80° 600 400 200 00 Zoo 400 600 8o"

(LEFT) A N G U l A R P O S i T l O N (R I GHT)

FIGURE 7. MULTIPURPOSE TLD ANGULAR RESPONSE TO 6 0 ~ o GAMMA RADIATION.

0 100 200 300 400 500 600

MULTI-PURPOSE TLD BADGE (mR)

FIGURE 8. PENETRATING DOSE COMPARISON - MULTIPURPOSE TLD VS. FILM BADGE.

0 100 200 300 400 500 600

MIJI T I -PURPOSE TbD BADGE (mR)

FIGURE 9 . DERMA DOSE COMPARISON - MULTIPURPOSE TLD VS. F ILM BADGE.

C d SH l ELD

TLD #4

. / NEUTRON @-@ A N D O f SOURCE \ s

TLD #3

NEUTRON ENERGY, MeV 6 FIGURE 11. THE Li(n,a) CROSS SECTION AS A FUNCTION OF NEUTRON ENERGY.

ENERGY, MeV

FIGURE 12. NEUTRON FLUX DENSITY AND DOSE DISTRIBUTION FOR AN UNMODERATED CRITICALITY EVENT.

-

-

-

-

-

- FLUX D E N S I T Y

-

-

I 1 A

ENERGY, MeV

FIGURE 13. NEUTRON FLUX DENSITY AND DOSE DISTRIBUTION FOR A HEAVILY MODERATED CRITICALITY EVENT.

50 100 lo00 10,000

NEUTRON ENERGY, keV

F I G U R E 1 5 . F A S T NEUTRON DOSE R E S P O N S E A S A F U N C T I O N O F NEUTRON ENERGY.

I

NORMALIZED TO 2 cm

0 PuF4

A 0.562 MeV VAN de GRAAFF - \ 0 - 0 0.120 MeV HARWELL - - - \ O i 0 '

-

-

C I I 1 1 1 . I I I 1 I

4 6 8

D I STANCE, cm

FIGURE 1 6 . FAST NEUTRON RESPONSE AS A FUNCTION OF THE DISTANCE BETWEEN THE MULTIPURPOSE BADGE AND THE SURFACE OF A POLYETHYLENE PHANTOM.

a FAST NEUTRONS. 2 5 2 ~ f SOURCE - 0 SLOW NEUTRONS *

81 mrad - I EACH

71 cm

1 -

- a - AA\ - 0-O A,--:

l o - o

I I I 1 I 0 FRONT FRONT S IDE BA CK BA CK

CENTER LEFT & R l GHT LEFT & R l GHT LEFT & R l GHT CENTER

P O S I T I O N 0.F BADGE F I G U R E 1 7 . F A S T AND THERMAL WEUTRON RESPONSE A S A FUNCTION O F THE P O S I T I O N O F

THE BADGE OW A REFAB PHANTOM.

0 AO o 4.5 M ~ V (VAN de GRAAFF NEUTRONS)

0 1.0 M e V (VAN de GRAAFF NEUTRONS) -

A 0.35 M e V (VAN de GRAAFF NEUTRONS)

-

-

-

-

-

-

I I 1 1 I

FRONT FRONT S I D E BA CK BA CK CENTER S IDE S I D E CENTER

FIGURE 18. RELATIVE MONOENERGETIC FAST NEUTRON RESPONSE AS A FUNCTION OF THE POSITION OF THE BADGE ON A PHANTOM. DATA HAVE BEEN NORMALIZED TO FRONT CENTER POSITION.

O '9th EACH EXPOSURE 81 mrad A .nf 00

22 -1120 i * * 4P

00 22 -11 2O 45O 67 -1120 900

P O S I T I O N OF SOURCE

F I G U R E 1 9 . F A S T NEUTRON R E S P O N S E A S A F U N C T I O N O F I N C I D E N T NEUTRON ANGLE.

. - TIME

I FIGURE 2 0 . GLOW CURVE FOR L i F AFTER A STANDARD READOUT CYCLE,.

FIGURE 2 1 . GLOW CURVE FOR 7 ~ i F AFTER EIGHT-DAY HOLDING PERIOD.

ELEVEN DAYS AT ROOM TEMPERATURE, EXPOSED AND READ

ELEVEN DAYS AT ROOM TEMPERATURE, EXPOSED AND READ OUT AT 45 DAYS.

- TIME -TIME

FOURTEEN DAYS AT ROOM TEMPERATURE, EXPOSED AND READ OUT.

TH I RTY -FI VE DAYS AT ROOM TEMPERATURE, - EXPOSED AND READ OUT.

- TIME - TIME

7 FIGURE 22. GLOW CURVES FOR LiF AFTER VARIOUS ANNEALING AND EXPOSURE CONDITIONS.

EXPOSED: 5/8/69 500 mR 2 2 6 ~ a 226 EXPOSED: 8/7/69 500 mR . Ra -

' (93 DAY.S LATTER -

ooo t: u X 0 0

0 0 - 0 0

0 0 -

TLD-700 RIBBON READER ANNEALED: 1123-3/19/69

1 1 1 I I 1 I I

0 EOO 200 300 400 500

DAYS SINCE EXPOSURE

F I G U R E 2 3 . ONE YEAR F A D I N G STUDY SHOWING R E S P O N S E O F 7 ~ i F E X P O S E D A F T E R ONE MONTH HOLDING P E R I O D A T ROOM TEMPERATURE.