The DL-alanine ESR dosimeter in the radiation processing

0146-5724/90 $3.00 + 0.00 Pergamon Press plc

Radiat. Phys. Chem. Vol. 35, Nos 4-6, pp. 783-788, 1990 Int. J. Radiat. Appl. Instrum., Part C Printed in Great Britain

THE D L - A L A N I N E Zhang

ESE D O S I M E T E R

Yinfen,

Institute

of

*Laboratory

Pan

Hongbin*,

IN THE R A D I A T I O N P R O C E S S I N G Xie

Liqing,

Zhou

Low E n e r g y N u c l e a r Physics,Bei.jing University,Beijing,China of Industrial Hygiene,Ministry of Health,Beijing,china

Ruiying

Normal Public

ABSTRACT In this paper, the b a s i c d o s i m e t r i c c h a r a c t e r s of the a l a n i n e / E S R d o s i m e t e r used in r a d i a t i o n p r o c e s s i n g is i n t r o d u c e d and the m e t h o d for p r e p a r i n g the d o s i m e t e r is d i s c u s s e d . An e x c e l l e n t l i n e a r i t y in the range of IOZGy---IO4Gy was observed. The linear correlation c o e f f i c i e n t b e t w e e n the a m p l i t u d e of the m a i n peak of ESR signal and the c o r r e s p o n d e n t dose is g r e a t e r than 0.9999. A s p e c i a l i n s t r u m e n t was d e s i g n e d for f i x i n g the lower end of the s a m p l e tube. It i m p r o v e d the s t a n d a r d d e v i a t i o n from ~ I . I ~ to ~ 0 . 4 5 ~ and the linear r e l a t i o n s between gain settings of the spectrometer were amended. The dispersivity of the signal amplitude for many of dosimeters with a dose of 1EGy was studied and the standard deviation of the signals was +0.55. The correction factor of dosimeters for the response value of t~e radiation temperature was 0.002l/°C.

KEYWORDS alanine

dosimeter;

ESR s p e c t r o m e t e r ;

absorbed

dose.

INTRODUCTION T h e h i g h dose ( I 0 2 G y - - I O 4 G y ) r a d i a t i o n p r o c e s s i n g of 6aCe g a m m a - r a y has been w i d e l y used. It needs a m e t h o d for a large range m e a s u r e m e n t . The m e t h o d d i s c u s s e d here is b a s e d on the r a d i a t i o n - i n d u c e d a l a n i n e free r a d i c a l s w h i c h is m e a s u r e d by ESR ( E l e c t r o n Spin R e s o n a n c e ) . It is an accurate, s t a b l e method. It p r o v i d e s u d o s i m e t e r w i t h a good reproducibility,small size and e x c e l l e n t r e p r e s e n t a t i v e effect w i t h the t i s s u e of l i v i n g bodies, b e i n g s u i t e d for the use in r a d i a t i o n p r o c e s s i n g and in d o s i m e t r y m a i l i n g i n t e r c o m p a r i s o n for ion radiation. As e a r l y as in 1962, an a l a n i n e / E S R d o s i m e t r y m e t h o d was used by B r a d s h a w et al. (I) , in m e a s u r i n g high dose. The m e t h o d has been i m p r o v e d by R e g u l l a et al. ta-a) and it has been d i s c u s s e d that by the accuracy the alanine/ESR dosimeter could be used as a transfer dosimeter. T . K o j i m a et el., t4) have s t u d i e d the c h a r a c t e r i s t i c s of a l a n i n e d o s i m e t e r s u s i n g p o l y m e r s as binders. D o s i m e t r i c p r o p e r t i e s of the D L - a ~ a n i n e / E S R d o s i m e t e r w e r e s t u d i e d by China. Ca-a) IAEA decided, not long ago, that the a l a n i n e / E S R be used as the I n t e r n a t i o n a l Dose A s s u r a n c e S e r v i c e of g a m m a - r a y r a d i a t i o n f a c i l i t i e s in the high dose m e a s u r i n g for the m e m b e r c o u n t r i e s of IAEA. In this work, a mixture of Model DL-alanine and paraffin was selected to make up the dosimeters and their dosimetric characteristics were studied. They were then used, in dosimetry m e a s u r e m e n t s for r a d i a t i o n p r o c e s s i n g at B e i j i n g R a d i a t i o n A p p l i c a t i o n Center. EXPERIMENTAL

PROCEDURES

1.Dosimeter preparation (1) The Material of the Dosimeter A reagent of model DL-alanine was selected. Its purity was more than 95~ and the molecular weight was 89.09. (2) The Preparation of the Dosimeter Dried alanine powder was ground, screened and homogeneously mixed with the pure screened paraffin powder in a ratio of 8;2. They put into moulds to be pressed into small cylinders, 3mm i n d i a m e t e r , 7mm i n length (Fig. l). It must place for ready use. 164 d o s i m e t e r s w e r e w e i g h e d on a n a c c u r a t e balance. The a v e r a g e m a s s was 7 0 . 4 6 m g and the s t a n d a r d d e v i a t i o n was +0.64mg. The mass f r e q u e n c y d i s t r i b u t i o n chart o b t a i n e d was a p p r o x i m a t e to a n o r m a l d i s t r i b u t i o n . 783

784

ZHANG Y]N~N et al.

Fig.l.

Alanine

dosimeters

2.1rradiations The i r r a d i a t i o n of the d o s i m e t e r was p e r f o r m e d in the i r r a d i a t i o n field of the 3.8xI014 Bq e ° C o g a m m a - r a y s o u r c e at B e i j i n g N o r m a l U n i v e r s i t y . It is c a l i b r a t e d by m e a n s of F r i c k e d o s i m e t e r in terms of an a b s o r b e d dose in water. The d u r a t i o n of i r r a d i a t i o n was c o n t r o l l e d by an e l e c t r o n i c timer 3 . G r a d u a t i o n of the D o s i m e t e r The free r a d i c a l s c o n c e n t r a t i o n in the a l a n i n e d o s i m e t e r i r r a d i a t e d is in p r o p o r t i o n to the i r r a d i a t i o n d o s e , b u t it is d i f f i c u l t to c a r r y out absolute m e a s u r e m e n t s . For this reason,at present,the method of r e l a t i v e g r a d u a t i o n is a d o p t e d , t h a t is,the alanine, w h i c h is e x a c t l y the same as that in the s a m p l e m e a s u r e d , is used as a " r e f e r e n c e s a m p l e " and g r a d u a t e d in a known r a d i a t i o n field. In our work, the a b s o r b e d dose rate D at the g r a d u a t i o n p o s i t i o n was equal to 0 . 3 6 G y S1. 4. The M e a s u r e m e n t of ESR Signal After b e i n g irradiated, the d o s i m e t e r was put into a tube, h a v i n g a thin wall, m a d e from q u a r t z and i n s e r t e d into a r e s o n a n t cavity. The measurement was carried out by a JES-FE-IXG spectrometer. The microwave frequency was 9425MHz. The magnetic field setting was 339mT, and the field scan range was 20mT. The temperature during measurement was 24oC. • The modulation amplitude was O.lmT and the power of the microwave was 2mW. In order to assure the reproducibility of the measurement of the sample, the upper and lower end of the sample tube were fixed and the position was strictly oriented for each m e a s u r e m e n t . The chart of the m e a s u r e d first d e r i v a t i v e for the E S R s p e c t r u m of a l a n i n e s a m p l e is shown in Fig.2.

2

3 4

I t4

Fig.2.

The ESR s p e c t r u m

5

°

of r - i r r a d i a t e d

DL-alanine

The middle peak amplitude is selected as the reading o f ESR s i g n a l . The values of the main peak amplitude all need to be normalized for the sample mass and the gain of the ESR s p e c t r o m e t e r , so as to eliminate the nonlinear effect between the mass dispersivity and the gain. The spectrometer was checked before and after every series of m e a s u r e m e n t s w i t h i r r a d i a t e d r e f e r e n c e a l a n i n e s a m p l e s that had been e x p o s e d to k n o w n r a d i a t i o n doses.

7th International Meeting on Radiation Processing

EXPERIMENT

785

RESULTS

1.The Reproducibility of Position-fixing Measurement for a Single Dosimeter After p r e h e a t i n g the s p e c t r o m e t e r , the d o s i m e t e r was put into the s a m p l e tube, i n s e r t e d into the r e s o n a n t c a v i t y and the p o s i t i o n fixed. It was m e a s u r e d c o n t i n u o u s l y for 40 times in 40 minutes. There w e r e some fluctuations for the signal amplitude and the response d i s p e r s i v i t y was in the range of =l}.22~ (Fig.3) w h i c h r e f l e c t e d the short term s t a b i l i t y of the RSR s p e c t r o m e t e r .

1.005

oe

Y~ ~.ooo

•

i •

~t

•

°•

ao

• •

•

oo

•

•

•o

•o

i

•/

0..9. I

e

Fig.3.

DispersivJty

~

n

20 Time ( m:l.n )

I0

of the r e s p o n s e

e

i

30

40

signal

~it.hin 40 m i n u t e s

2. 'rile IteproducibJ l J t , y ,,l' M e a s u r e m e n l u n d e r the C o n d i t i o n ot ' T a k i n g out and P u t t i n g in The position oI" t h e d e s i m e l : e r ix, I.he r e s o n a n t cavity would affect the reproducibility of the signal amp||.rude directly. Therefore, tile upper end of the sumple tube was fixed by a f:ixture and the sample tube situated in the sensitive region of the cavity. The dosimeter was taken out: f r o m |:he cavity after being measured once. It was then put into the cavity and measured again. The relative standard deviation of single meesuremeat for eight t:imes measurement was 1.1~. In order to improve the accuracy, a special instrument was designed for fixing the lower end of the sample tube, as shown in Fig.4. For the same sample in the eight times measurement the relative standard deviation of single measurement become 0.45~. This indicated that the reproducibility of the position of the dosimeter was obviously i m p r o v e d and the m e a s u r i n g a c c u r a c y elevated.

3. Tile D:ispersivity of the Signal Amplitude for Multi-doslmeters Two groups of d o s i m e t e r were e x p o s e d in a r a d i a t i o n field and each group was irradiated with the same absorbed dose, and their signal amplitudes measured at the ESR spectrometer.. The results are e x p r e s s e d in table.l. Table.l. The d i s p e r s i v i t y of the signal a m p l i t u d e for a group of d o s i m e t e r samples. Absorbed dose

Number samples

of

M e a n value o1' signal a m p l l t u d e

(Gy) i0 3 5 x l O

2

Relative standard d e v i a t i o n of s i n g l e (~)

12

ll12.7

0.55

12

lJOO.H

0.80

786

Zrt~qo Y l ~

et al.

I

l',L

v

4

4

, ,,

5

I !

I !

(a)

(b)

F i g . 4 . The p o s i t i o n o f t h e s a m p l e t u b e :in t h e ( a ) The u p p e r e n d o f t i l e s a m p l e t u b e i s f i x e d . ( b ) The u p p e r e n d : l o w e r e n d o f t i l e s a m p l e t u b e a r e 1--sample tube, 2--fixture fixing the upper end, 3---resonant cavil:y, 4.--samp:l e, 5--instrument fixing the Lower end. 4.Temperature effect The e f f e c t on t h e r e s p o n s e of elevated temperature was i n v e s t i g a t e d at t e m p e r a t u r e s from 0oc to 50°C 1200Gy, the results ere shown in Fig.5.

resonant

cavity

fixed.

during irradiation and with a dose of

I

I

t

!

10

20

30

40

Tl'c}

Fig.5. Influence of t e m p e r a t u r e a m p l i t u d e of the elanine.

during

irradiation

on

the

ESR

signal

Figure 5 shows an increasing ESR signe] amplitude with rising temperature. The i n c r e a s i n g degrees r e g r e s s e d though a straight llne end c o r r e c t i o n factor for the effect of t e m p e r a t u r e on the ESR signal amplitude w as obtained, i.e. 0 . 0 0 2 1 o c -I.

7th International Meeting on Radiation Prnccssing

5.Dose response curve The r e l a t i o n s h i p between ESR s i g n a l amplitude and absorbed dose is shown in F i g . 6 w l t h t h e dose range form 102Gy to 3xlO4Gy. I n - f a c t , the a m p l i t u d e i n c r e a s e s l i n e a r l y w i t h d o s e r a n g e of 102 -- 3 x l O 4 G y for all d o s i m e t e r . At doses above 104Gy, the formation of radiation i n d u c e d r a d l c a l s in a l a n i n e s t a r t s to s a t u r a t e a n d t h e r e f o r e the d o s e response becomes sub-linear.(S)At d o s e s b e l o w 50Gy, the r a d i c a l y i e l d deviates from the linear relation against dose. (s) However, experiments indicate that in the range of 102Gy-I04Gy and the linear correlation coefficient between the ESR signal amplitude and c o r r e s p o n d e n t d o s e was g r e a t e r than 0 . 9 9 9 9 .

I04

I-

I

// ,-d

I0'I

I

102 @ e~ .e4

I IO s

I0 10 2

I 104

lu dr

Dose(Gy)

Fig.6.

Dose

response

curve

6.The Revised Values of Gain Factors f o r ESR S p e c k r o m e t e r Because the alanine/ESR dosimeter is applicable in a wide range of the dose for measuring, it is necessary to change various samples irradiated with different dose, so as to obtain proper signal amplitude. We a c c u r a t e l y traced tile proportional relationship among the gain factors and selected the adaptation value ("lx" for prc.-fRctor, "xl00" for decimal factor) as the normalization point. The a c c u r a t e l y revised values of gain factors are shown in Table.2. T a b l C . 2 . The

revised

Pre-factor

vn|ue.9

o{" g a i n

decimal

I

fact:ors

for

factor

I0

I00

1 1.25 1.6

0.9760 1.234 1.547

10.03 12.67 15.89

IO0.O 126.3 158.4

2.0 2.5

1.945 2.462 3.063 3.881 4.848

19.97 25.28

199.1 252.0

31.44 39.85 49.78 63.36 78.92 100.3

313.5 397.3 496.3 631.7 786.8 I000

3.2 4.0 5.0 6.3 7.9 I0

6.171 7.686 9.769

ESR s p e c t r o m e t e r

787

788

ZHANG YINFEN et al.

DISCUSSION Tile f r e e r'ad:i(:als of al nni ne J nduced by r o d ] atJ oil a r e v e r y stable. Samples kept at room t e m p e r a t u r e under day c o n d i t i o n were m e a s u r e d after about one month for th[~i r signal amplitude with the same reference sampte and these values for the most part corresponded to the originally measured ones in the range of =1~, with an exception of two points which were greater than 2~. Results of our investigations indicate a high dose range for the alanine dosimeter of 102-3xlOaGy. The response at elevated temperature increases at most by about 10~ over a temperature range f r o m O0C t o 50°C. The response in the linear dose-response region is stable. Due to the very broad usable dose range, the alanine/ES8 dosimeter proves convenient for radiation technology, this technique enables direct determination of absorbed dose on tissue-equivalent materials. The d o s i m e t e r is r u g g e d , non toxic, i n s e n s i t i v e to surface c o n t a m i n a t i o n s and can be e v a l u a t e d repeatedly. Careful sample p r e p a r a t i o n permits e x c e l l e n t b a t c h h o m o g e n e i t y at low cost of the dosimeter. It can be used as a t r a n s f e r d o s i m e t e r and w i d e l y used for high dose m e a s u r e m e n t in r a d i a t i o n processing.

REFERENCES

(i) B r a d s h a w W.W., C a d e n a D.G., G r a w f o r d G.W. and S p e t z l e r H.A.W. Radiat. Res 17,11 ( 1 9 6 2 ) (2) R e g u l l a D.F.and Deffner U., Int. J. AppI. Rad]at. Isot. 3 3 , ] 1 0 1 (1982) ( 3 ) R e g l l a D.F. and D e f f n e r If., IAEA-SM-272/39 (1984) (4) Janovsky I., Hansen J.W., Cernoch P., Appl. Radiat. Isot. 39,

651

(1988) (5) K o j i m a T., Tanaka R., M e r i t s Y. and SeguchJ T., Appl. Radiat. Isot. 37, 517 (1986) (6) C u n p u Sun, Jinjun Dang, Y u a n m i n g Shi, ACTA M E T R O L O G I C A SINICA.

4,213

{1983)

(7) Z h o n g i u n

Zhang

and C h e n g x i a n g

Liu,ACTA

METROLOGICA

SINICA.8,

194

(1987) (8) J u n e h e n g G a o , Peigen Sheng, Zhimin Shen, Z a i y o n g Wang and Ruali Wang, C h i n e s e Journal of M i c r o w a v e and R a d i o - f r e q u e n c y Spectroscopy. 4, 161 (1987) (9) D e f f n e r U.and R e g u ; ; a D.F. Nulear Instruments and Methods 175,134 (1980) (10) Simmons J.h.and Bewley D.g. Radiation Research 65, 197-201 (1976)