The Oxalic Acid Dosimeter Procedure - ACS Publications

39 The Oxalic Acid Dosimeter Procedure NIELS W. HOLM and K. SEHESTED

Downloaded by UNIV OF ROCHESTER on June 12, 2018 | https://pubs.acs.org Publication Date: January 1, 1968 | doi: 10.1021/ba-1968-0081.ch039

The Danish Atomic Energy Commission, Research Establishment Risö, Roskilde, Denmark

A review is given on the experiences with the oxalic acid dosimeter.

The system was first suggested by Draganić,

who has carried out extensive investigations on the dosi metric properties. Further experiments have been carried out at various laboratories—e.g., in the United States, Japan, and Denmark. Although the system suffers from some sys tematic weaknesses, it can be applied successfully, when properly calibrated under the conditions where it is to be used. The present report describes its application for and

60

Co

high dose-rate electron dosimetry.

>Tphe o x a l i c - a c i d dosimeter has a h i s t o r y c o m p a r a b l e to that of t h e ceric-sulfate dosimeter.

M u c h w o r k has b e e n c a r r i e d out, p r o m i s

i n g results h a v e b e e n o b t a i n e d , a n d a n a b u n d a n c e of p u b l i c a t i o n s have a p p e a r e d ; b u t o n l y f e w p e o p l e r e a l l y use these systems.

Still both the

ceric-sulfate dosimeter a n d t h e o x a l i c - a c i d d o s i m e t e r m a y b e a p p l i e d successfully, o n c e t h e y a r e " d e b u g g e d " b y t h e p e o p l e w h o a r e to use t h e m i n the d a i l y r o u t i n e . B o t h systems deserve m u c h a t t e n t i o n as t h e y are a m o n g the f e w p r o m i s i n g candidates o f aqueous c h e m i c a l dosimeters for use i n the m e g a r a d range. T h e o x a l i c - a c i d d o s i m e t e r has some s u b s t a n t i a l advantages o v e r t h e ceric-sulfate (1)

dosimeter,

which

made

us investigate

it more

closely:

i t is q u i t e insensitive t o i m p u r i t i e s , ( 2 ) i t h a s v e r y g o o d energy-

a b s o r p t i o n characteristics, a n d ( 3 ) t h e system is v e r y stable t o n o r m a l storage b e f o r e a n d after i r r a d i a t i o n . T h e system also has some d r a w b a c k s : ( 1 ) t h e d e c o m p o s i t i o n of o x a l i c - a c i d does not p r o c e e d l i n e a r l y w i t h t h e a b s o r b e d dose, a n d ( 2 ) t h e c h e m i c a l y i e l d is n o t f u l l y i n d e p e n d e n t of the r a d i a t i o n c o n d i t i o n s . O t h e r difficulties h a v e b e e n r e p o r t e d a n d h a v e h a m p e r e d the p r a c t i c a l use. T h i s p a p e r identifies some of these difficulties a n d suggests p r a c t i c a l solutions. O n basis of n e w e r e v i d e n c e , i t is b e l i e v e d b y the authors that 568 Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

39.

H O L M AND SEHESTED

Oxalic Acid

569

Dosimeter

the system is v e r y w e l l s u i t e d f o r d o s i m e t r y in—e.g., r a d i a t i o n s t e r i l i z a t i o n of f o o d a n d m e d i c a l p r o d u c t s . Historical

Background

T h e system w a s first d e s c r i b e d i n 1955 ( 3 ) b y D r a g a n i c , w h o p o i n t e d out the advantages l i s t e d above.

I n later p u b l i c a t i o n s (4, 6, 7, 11), d e

t a i l e d procedures w e r e r e p o r t e d f o r

6 0

C o as w e l l as f o r reactor use.


T h e r o u t i n e p r o c e d u r e w a s b a s e d o n the f o l l o w i n g : ( 1 ) T h e oxalic a c i d decomposes w h e n subjected to r a d i a t i o n , a n d the a b s o r b e d dose is d e t e r m i n e d f r o m t h e decrease i n o x a l i c - a c i d c o n c e n tration upon irradiation. ( 2 ) T h e o x a l i c - a c i d c o n c e n t r a t i o n measurements are p e r f o r m e d b y ( a ) K M n 0 titration ( 3 ) , ( b ) cupribenzidine spectrophotometry (11), or ( c ) N a O H t i t r a t i o n (19). 4

( 3 ) T h e c h e m i c a l change is n o t a l i n e a r f u n c t i o n of t h e dose. A s a n a p p r o x i m a t i o n i t w a s suggested to use G = 4.9 u p to 3 0 % d e c o m p o s i t i o n , a n d f r o m t h e n o n calculate the dose f r o m a n expression of the f o r m log D = a log C + b, w h e r e D is the a b s o r b e d dose i n e . v . / g r a m , C the n u m b e r of m o l e c u l e s d e c o m p o s e d p e r g r a m , a n d a a n d b constants d e p e n d i n g o n t h e oxalica c i d c o n c e n t r a t i o n b e f o r e a n d after i r r a d i a t i o n . O n this basis the system w a s u s e d successfully at t h e laboratories at R i s o a n d V i n c a ( B o r i s K i d r i c h Institute of N u c l e a r Sciences, B e l g r a d e , Yugoslavia). accurate,

W h i l e t h e K M n 0 - t i t r a t i o n m e t h o d w a s d i s c a r d e d as less 4

the c u p r i b e n z i d i n e m e t h o d w a s d e v e l o p e d f u r t h e r

(11)

and

p r o v e n to b e satisfactory f o r r o u t i n e use. T h e N a O H t i t r a t i o n w a s c o n s i d e r e d a g o o d alternative m e t h o d .

T h e G - v a l u e f o r less t h a n 3 0 % d e

c o m p o s i t i o n w a s r e - d e t e r m i n e d at V i n c a (20) independent Concurrent

b y calorimetry, a n d a n

G - v a l u e d e t e r m i n a t i o n w a s c a r r i e d out elsewhere investigations

for pulsed

electron

beams

took

(15).

place

at

Riso ( 9 ) . D u r i n g these years, the system g a i n e d interest i n the U n i t e d States (6)

as a p r o s p e c t i v e substitute f o r the ceric-sulfate dosimeter i n f o o d -

i r r a d i a t i o n d o s i m e t r y . A n A S T M ( A m e r i c a n Society f o r T e s t i n g & M a t e r i a l s ) s u b c o m m i t t e e d e a l i n g w i t h d o s i m e t r y p r o b l e m s w o r k e d out tenta tive recommended

procedures,

n u m b e r of laboratories.

a n d circulated them

T h e suggestions

f o r testing

f o r the a n a l y t i c a l

in a

procedure

included both spectrophotometry a n d N a O H - t i t r a t i o n . First ASTM

Round

Robin Test

T w o m e m b e r s of t h e A S T M - c o m m i t t e e h a v e p u b l i s h e d the results of their investigations.

Glass (13)

f o u n d that t h e s p e c t r o p h o t o m e t r i c p r o -

Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

570

RADIATION CHEMISTRY

1

c e d i i r e y i e l d e d results 7 - 1 6 % l o w e r t h a n those o b t a i n e d b y the F r i c k e dosimeter.

I n the t i t r a t i o n p r o c e d u r e , the results w e r e 2 - 6 %

lower.

T h e s e measurements c o m p r i s e d 100 m M , 300 m M , a n d 750 m M oxalica c i d solutions. C o n n a l l y a n d G e v a n t m a n n (2)

u s e d the s p e c t r o p h o t o m e t r i c m e t h o d

a n d f o u n d , w i t h i n ± 5 — 1 0 % , agreement w i t h values e x t r a p o l a t e d f r o m measurements w i t h the F r i c k e dosimeter. H a r m e r (14)

a n d W e i s s (22)

h a d i n d i c a t i o n s of i n s t a b i l i t y to u l t r a

v i o l e t l i g h t of the d i l u t e d c o m p l e x s o l u t i o n f o r the s p e c t r o p h o t o m e t r i c Downloaded by UNIV OF ROCHESTER on June 12, 2018 | https://pubs.acs.org Publication Date: January 1, 1968 | doi: 10.1021/ba-1968-0081.ch039

measurement. C h e e k a n d L i n n e n b o m ( 1 ) f o u n d f o r the s p e c t r o p h o t o m e t r i c m e t h o d s t a n d a r d d e v i a t i o n s of the o r d e r of ± 1 0 % b a s e d o n a G - v a l u e of 4.9. F o r the N a O H - t i t r a t i o n m e t h o d t h e y effective r e m o v a l o f C 0

2

emphasized the importance

of

f r o m the i r r a d i a t e d s o l u t i o n . A s a n alternative

to h e a t i n g t h e y p r o p o s e d to r e m o v e the C 0

2

b y p u r g i n g the s o l u t i o n

w i t h a stream of H 0 - s a t u r a t e d , C 0 - f r e e a i r . B y t i t r a t i o n t h e y f o u n d 2

2

the G - v a l u e to b e 4.4 f o r a 75 m M o x a l i c - a c i d s o l u t i o n . Fenger

u s e d the dosimeter f o r g a m m a - f l u x measurements i n

(12)

the t h e r m a l c o l u m n of the D R 2 reactor a n d c a l i b r a t e d the system i n the R i s o C o - 6 0 f a c i l i t y . H e f o u n d f o r a 50 m M o x a l i c - a c i d s o l u t i o n a G - v a l u e of 4.6 ± 0.3. T h e earlier experiences of this l a b o r a t o r y w e r e g o o d i n so f a r as the a c c u r a c y o b t a i n e d w i t h the system w a s i n a c c o r d a n c e w i t h w h a t h a d b e e n stated b y D r a g a n i c (better t h a n 1 0 % ). T h e d i f f i c u l t y i n o b t a i n i n g good

results

procedure.

as r e p o r t e d

above,

however,

made

us re-examine

the

( T h i s w o r k w a s started b y one of the authors ( N . W . H . )

d u r i n g a one-year

stay as v i s i t i n g scientist

at t h e R a d i a t i o n

Sources

B r a n c h of the U . S . A r m y N a t i c k L a b o r a t o r i e s , N a t i c k , M a s s . , U n i t e d States. ) Re-examination

of

Procedure

T h e i n f o r m a t i o n a c c u m u l a t e d b y the first A S T M r o u n d r o b i n test i n d i c a t e d t w o k i n d s of d i f f i c u l t i e s : ( 1 ) T h e scattering of results i n i n d i v i d u a l tests at a n y p a r t i c u l a r l a b o r a t o r y i n d i c a t e d that t h e a n a l y t i c a l p r o c e d u r e w a s either too c o m p l i c a t e d f o r r o u t i n e use, or i n a c c u r a t e o w i n g to systematic errors—e.g., i n s t a b i l i t y to u l t r a v i o l e t l i g h t of the c u p r i b e n z i d i n e c o m p l e x s o l u t i o n . ( 2 ) A p p l i c a t i o n of G = 4.9 f o r 0 - 3 0 % d e c o m p o s i t i o n a n d of t h e l o g - l o g e q u a t i o n d i d n o t fit t h e true d e c o m p o s i t i o n c u r v e a d e q u a t e l y . Analytical Procedures. T h e d e m a n d s o n the c h e m i c a l analysis are v e r y strict as the a b s o r b e d dose is d e t e r m i n e d as a difference b e t w e e n t w o concentrations. T h r e e a n a l y t i c a l m e t h o d s h a v e b e e n suggested f o r use i n o x a l i c - a c i d d o s i m e t r y :


39.


Oxalic Acid

Dosimeter

571

( 1 ) TITRATION WITH K M N 0 (4, 6). T h i s m e t h o d is n o t v e r y spe cific as h y d r o g e n p e r o x i d e a n d o r g a n i c b y - p r o d u c t s f o r m e d b y the r a d i olysis are t i t r a t e d together w i t h the oxalic a c i d . G o o d r e p r o d u c i b i l i t y is d e p e n d e n t u p o n a subjective k i n d of r o u t i n e o n the p a r t of the operator, a n d the m e t h o d is therefore not c o n s i d e r e d s u i t a b l e as a s t a n d a r d dosimetry procedure. 4


(2)

SPECTROPHOTOMETRY

OF

THE

CUPRIBENZIDINE

COMPLEX

OF

O X A L I C A C I D (4, 5,6). Z . D r a g a n i c a n d I. D r a g a n i c (10,11) h a v e d e v e l o p e d a m e t h o d f o r s p e c t r o p h o t o m e t r i c d e t e r m i n a t i o n of o x a l i c a c i d b y means of a reagent m a d e u p of a n aqueous s o l u t i o n of c u p r i c acetate, b e n z i d i n e d i h y d r o c h l o r i d e , a n d acetic a c i d . T h e o x a l i c - a c i d s o l u t i o n is d i l u t e d a n d m i x e d w i t h the c o m p l e x i n g reagent, a n d the o p t i c a l d e n s i t y is r e a d at 2 4 6 τημ. T h e m o l a r e x t i n c t i o n coefficient of t h e c o m p l e x is r e p o r t e d to be 2490, a n d it is stated that it m a y v a r y w i t h i n 1 0 % f r o m b a t c h to b a t c h a c c o r d i n g to reagent p u r i t y (6). A negative temperature coefficient of 0 . 7 % / ° C . is r e p o r t e d for the c o m p l e x a n d the c e l l c o m p a r t m e n t s h o u l d therefore b e t e m p e r a t u r e c o n t r o l l e d . ( 3 ) T I T R A T I O N W I T H N A O H . T h i s m e t h o d w a s suggested b y M a t s u i ( 1 9 ) , w h o r e m o v e d the c a r b o n d i o x i d e f r o m the i r r a d i a t e d s o l u t i o n b y h e a t i n g the s a m p l e i n a w a t e r b a t h f o r 3 0 m i n u t e s . O t h e r experimenters (6, 13, 17) h a v e c h e c k e d this m e t h o d , b u t the agreement o b t a i n e d w a s not q u i t e satisfactory. T h e reason seems to b e i n a d e q u a t e r e m o v a l of carbon dioxide. T h e experiments at N a t i c k a n d at R i s e r e g a r d i n g the a n a l y t i c a l p r o cedures gave the f o l l o w i n g results (9): ( 1 ) S P E C T R O P H O T O M E T R Y . T h e a n a l y t i c a l reagents w e r e p r e p a r e d as d e s c r i b e d b y D r a g a n i c et al. (5) a n d the a n a l y t i c a l p r o c e d u r e w a s c h e c k e d b y p r e p a r i n g a set of 0.1, 0.2, a n d 0.3 m M o x a l i c - a c i d c o m p l e x solutions. T h e measurements w e r e c a r r i e d out o n a G a r y m o d e l 15, d u a l b e a m spectrophotometer ( N a t i c k ) a n d o n a Zeiss P M Q I I s i n g l e - b e a m spectrophotometer ( R i s e ) , b o t h w i t h t e m p e r a t u r e - c o n t r o l l e d c e l l c o m partments. A c a l i b r a t i o n c u r v e o b t a i n e d w i t h t h e s t a n d a r d D r a g a n i c ( 5 ) reagent is s h o w n i n F i g u r e 1. T h e O . D . of a 0.1 m M o x a l i c - a c i d c o m p l e x s o l u t i o n w a s d e t e r m i n e d to b e 0.250 ( c o r r e s p o n d i n g to a m o l a r e x t i n c t i o n coeffi cient of 2 5 0 0 ) . A s s u m i n g L a m b e r t - B e e r ' s l a w to b e v a l i d i t w a s t h e n expected that the O . D . of a 0.2 m M a n d 0.3 m M w o u l d b e 0 . 5 0 0 a n d 0.750 respectively. T h e readings, h o w e v e r , w e r e persistently h i g h e r , n a m e l y 0.530 a n d 0.815. T h i s w a s o b s e r v e d at b o t h laboratories a n d c h e c k e d i n several d e t e r m i n a t i o n s . ( I n a c c e l e r a t o r - i r r a d i a t e d solutions w e f o u n d that some of the r e a c t i o n p r o d u c t s f r o m the r a d i o l y s i s h a d a n a b s o r p t i o n of t h e i r o w n , w h i c h i n t e r f e r e d ( u p to 5 - 1 0 % ) w i t h the o x a l i c - a c i d deter m i n a t i o n . ) A systematic i n v e s t i g a t i o n w a s u n d e r t a k e n to c l a r i f y w h e t h e r other s t o i c h i o m e t r i c c o m p o s i t i o n s m i g h t l e a d to a better straight-line r e l a t i o n s h i p . It w a s f o u n d that the f o l l o w i n g concentrations gave a better a p p r o x i m a t i o n to a straight l i n e : ( 1 ) Solution A: D i s s o l v e 51.4 m g . b e n z i d i n e h y d r o c h l o r i d e i n 1 0 m l . 3 0 % v o l . acetic a c i d a n d d i l u t e w i t h d i s t i l l e d w a t e r to 2 5 0 m l . ( 0 . 8 m M ) ; a n d ( 2 ) Solution B: D i s s o l v e 159.7 m g . c u p r i c acetate i n 2 5 0 m l . d i s t i l l e d w a t e r ( 3 . 2 m M ) .



572

RADIATION CHEMISTRY

1

T h e m o l a r e x t i n c t i o n coefficient of the c o m p l e x w a s 2100. T h e re agent w a s u s e d i n a 1:4 ratio as earlier. T h e s t a b i l i t y of the reagent has b e e n q u e s t i o n e d b y some users, a n d a test w a s m a d e to examine this p r o b l e m . A set of solutions A a n d Β was stored f o r one m o n t h . A n o t h e r set of solutions w a s m i x e d to ( A + B ) a n d s i m i l a r l y stored. A f t e r the storage p e r i o d a f r e s h set of reagents was p r e p a r e d , a n d a l l three sets of reagents w e r e tested. T h e y gave i d e n t i c a l r e a d i n g s , b u t the p r e m i x e d a n d stored reagent w a s u n s t a b l e i n the spectrophotometer. A n o t h e r k i n d of i n s t a b i l i t y was o b s e r v e d i n the w o r k w i t h the C a r y s p e c t r o p h o t o m e t e r at N a t i c k . T h e O . D . readings decreased as i f a d e c o m p o s i t i o n of the c o m p l e x was t a k i n g place. T h i s p h e n o m e n o n was not o b s e r v e d w i t h the s i n g l e - b e a m spectrophotometer at R i s o . A s i m p l e test i n w h i c h a c o m p l e x s o l u t i o n was exposed to intense u l t r a v i o l e t l i g h t s h o w e d that a f e w m i n u t e s ' exposure decreased the o p t i c a l d e n s i t y some 5 0 % . A p r o c e d u r e , w h i c h takes care of this p r o b l e m is d e s c r i b e d i n Ref. 25. N A O H T I T R A T I O N . T h e o n l y p r o b l e m w i t h this m e t h o d is the q u a n t i tative r e m o v a l of C 0 , p r o d u c e d b y the d e c o m p o s i t i o n of oxalic a c i d . P u r g i n g of the s o l u t i o n w i t h w a t e r - s a t u r a t e d air w o r k s w e l l . A n easier m e t h o d is to take a n a l i q u o t f r o m the i r r a d i a t e d sample, w e i g h it, d i l u t e w i t h d i s t i l l e d w a t e r , a n d heat the s o l u t i o n for 30 m i n u t e s before t i t r a t i o n . 2


39.


Oxalic Acid

Dosimeter

573

C O N C L U S I O N . T h e experiments s h o w e d that t h e s p e c t r o p h o t o m e t r i c m e t h o d as w e l l as t h e t i t r i m e t r i c m e t h o d c o u l d r e n d e r r e p r o d u c i b l e r e sults ( w i t h i n ± 2 - 3 % ) . T h e t i t r i m e t r i c m e t h o d m a y b e p r e f e r r e d as b e i n g m o r e r e l i a b l e a n d s i m p l e i n r o u t i n e use. Decomposition Curve. T h e refinements i n the a n a l y t i c a l p r o c e d u r e p e r m i t t e d a m o r e a c c u r a t e d e t e r m i n a t i o n of t h e o x a l i c - a c i d d e c o m p o s i t i o n c u r v e . T h e e x p e r i m e n t a l d a t a d e m o n s t r a t e d that t h e y i e l d decreases c o n t i n u o u s l y w i t h i n c r e a s i n g dose t h r o u g h o u t t h e d e c o m p o s i t i o n range. A d e c o m p o s i t i o n c u r v e f o r a 100 m M o x a l i c - a c i d s o l u t i o n o b t a i n e d at R i s o is s h o w n i n F i g u r e 2. ANx10" mol/ i


,8

m

Riso 100mM oxalic acid

40

32

24

16 Δ = spectre^photometry Ο = titratio η 8

Dx10- ev/ 9 , 16 M

"θ

4

8

12

Figure 2. Calibration curve for oxalic-acid de composition vs. absorbed dose as determined by titration and by spectrophotometry for 100 mM oxalic acid D r a g a n i c suggested ( 8 ) that first order r e a c t i o n kinetics w o u l d a p p l y for t h e r a d i o l y t i c d e c o m p o s i t i o n . S u c h a r e l a t i o n corresponds v e r y w e l l w i t h t h e e x p e r i m e n t a l results o b t a i n e d at R i s o a n d at V i n c a as seen i n F i g u r e s 3 a , 3 b , a n d 3c. T h e d a t a


574

RADIATION

CHEMISTRY

1

f r o m the t i t r a t i o n analysis are u s e d as they are c o n s i d e r e d t o b e m o r e accurate. R e c e n t d a t a o b t a i n e d at V i n c a (18) b y s p e c t r o p h o t o m e t r y are plotted for comparison.

0.8

50mM oxalic acid

togSc

Δ


0.6 - o - Natick -Δ-

Risô

-χ-

Vinca

1 M Ci

Δ

10 k Ci 2 kCi

χ

A,^^

0.4

^

Ο

—^ x

0.2

D * ev/g »10" 1

2

3

4

5

20

6

Figure 3a. Calibration curves for oxalic-acid decomposition (log c /c vs. absorbed dose) obtained at Natick, Risô and Vinca (Ref. 18) 0

CONCLUSION.

F r o m F i g u r e s 3a, 3 b a n d 3c, i t m a y b e seen t h a t :

( 1 ) T h e v a l i d i t y of a l o g a r i t h m i c e q u a t i o n is s u p p o r t e d b y a l l t h e e x p e r i m e n t a l data. ( 2 ) A systematic bend-off of d a t a f r o m the straight l i n e c a n b e seen at h i g h e r d e c o m p o s i t i o n values, o w i n g to the b u i l d - u p of r a d i o l y t i c b y - p r o d u c t s w h i c h take p a r t i n the process. T h i s sets a n u p p e r l i m i t of a p p r o x . 6 0 % d e c o m p o s i t i o n to the range of u s e f u l a p p l i c a t i o n o f the dosimeter at a p a r t i c u l a r i n i t i a l c o n c e n t r a t i o n . ( 3 ) Results o b t a i n e d at the different installations s h o w different yields—i.e., different p r o p o r t i o n a l i t y factors i n a l o g a r i t h m i c e q u a t i o n . It is b e l i e v e d that the differences i n y i e l d b e t w e e n the different i n s t a l l a tions m a y b e caused b y a " l e n g t h of i r r a d i a t i o n " effect. A m o n g t h e first p r o d u c t s f o r m e d are g l y o x a l a n d g l y o x y l i c a c i d (21), w h i c h react f u r t h e r i n s l o w c o n d e n s a t i o n reactions. W h e n the i r r a d i a t i o n t i m e is of t h e same o r d e r o f m a g n i t u d e — o r l e s s — t h a n the " l i f e t i m e " of g l y o x a l a n d g l y o x y l i c a c i d i n the s o l u t i o n , these p r o d u c t s w i l l react to a greater extent w i t h t h e p r i m a r y r a d i c a l s thus decreasing the y i e l d . F o r t h e c o n d i t i o n s e x a m i n e d here the difference i n y i e l d c a n b e m o r e t h a n 1 0 % .


39.


Oxalic Acid

575

Dosimeter

100 mM oxalic acid 0.8

0.6 -o-

Natick

1 M Ci

- Δ -

Riso

10 I

χ

Vinca


0.4

0.2

Figure 3b. Calibration curves for oxalic-acid decomposition (log c /c vs. absorbed dose) obtained at Natick, Riso and Vinca (Ref. IS) G

log :

200 mM oxalic acid

0.8

Δ Risô Q6

χ Vinca

10 k Ci 2 k Ci

Q4

02

Dx10' ev/g 20

12

16

20

24

Figure 3c. Calibration curves for oxalic-acid decomposition (log c /c vs. absorbed dose) obtained at Natick, Riso and Vinca (Ref. IS) 0


576

RADIATION CHEMISTRY

Second ASTM

1

Round Robin Test

T h e s e c o n d r o u n d r o b i n test w h i c h took p l a c e i n 1966 w a s b a s e d o n a proposed procedure w o r k e d out b y H o l m

(15).

F i v e laboratories i n

t h e U n i t e d States took p a r t i n testing the p r o c e d u r e , w h i c h was b a s e d o n NaOH-titration.

It s h o w e d that laboratories a c c u s t o m e d to w o r k i n g o n

a n a l y t i c a l - c h e m i c a l p r o b l e m s got f a i r l y consistent a n d r e p r o d u c i b l e re sults. W h e n the results w e r e r e c a l c u l a t e d so as to express a values, these values r a n f r o m 37 to 49 (16).

A t V i n c a w h e r e these d a t a w e r e c o m p i l e d


f o r c o m p a r i s o n , the dose r e l a t i o n is u s e d i n the f o l l o w i n g f o r m : D = -c a

0

log^-.

D is the a b s o r b e d dose i n e.v./grams, a a p r o p o r t i o n a l i t y factor a n d

c

0

a n d c the concentrations i n m o l e c u l e s p e r m l . b e f o r e a n d after i r r a d i a t i o n .

Figure 4. Dose-rate dependence of 50 m M , 100 mM and 200 mM oxalicacid solutions, plotted as the number of molecules decomposed per unit energy input vs. the distance in centimeters from the beam exit window

Conclusions for

Co

60

Dosimetry

E x p e r i e n c e has s h o w n that the o x a l i c - a c i d dosimeter is not as s i m p l e i n use as o r i g i n a l l y a n t i c i p a t e d . T h e m o r e recent experiments h a v e l e d to refinements i n the a n a l y t i c a l p r o c e d u r e s a n d a d d e d to the u n d e r s t a n d i n g of the d e c o m p o s i t i o n process. It is necessary t h o u g h to c a l i b r a t e the system u n d e r the c o n d i t i o n s w h e r e it is to b e u s e d . W h e n that is d o n e , the system c a n b e expected to r e n d e r precise, r e l i a b l e a n d s i m p l e service.


39.


Application

Oxalic Acid

of the Oxalic-Acid

577

Dosimeter

Dosimeter for High Dose-Kate

Work

A n u m b e r of experiments h a v e b e e n c a r r i e d o u t at Risô (8, 9) o n the b e h a v i o r of the o x a l i c - a c i d system at extreme h i g h dose rates. T h e results of those experiments are s u m m a r i z e d i n F i g u r e 4, w h i c h shows the n u m b e r of m o l e c u l e s d e c o m p o s e d p e r u n i t energy i n p u t vs. t h e distance i n c m . f r o m the b e a m exit w i n d o w . B a s e d o n a dose c a l i b r a t i o n , these figures c o u l d b e r e c a l c u l a t e d so as to express the y i e l d as a f u n c t i o n of dose rate i n t h e p u l s e at a t o t a l d e c o m p o s i t i o n of 2 5 % .

It w a s f o u n d


that the d e c o m p o s i t i o n f o r a g i v e n dose is i n d e p e n d e n t of dose rate u p to : 2 X 1 0 rads/sec. for 50 m M oxalic acid 8

2 X 1 0 rads/sec. for 100 m M oxalic acid 9

2 X 10

1 0

rads/sec. for 200 m M oxalic acid

It is i m p o r t a n t t o note that t h e system is o n l y safe i n a r e a s o n a b l y homogeneous

field.

I n a v e r y i n h o m o g e n e o u s field a large s p e c t r u m of

t o t a l a b s o r b e d doses is f o u n d i n t h e s a m p l e a n d therefore also large differences i n c h e m i c a l y i e l d s .

Literature Cited (1) Cheek, Linnenbom, Naval Research Laboratory, Washington, D.C.,pri vate communication (1964). (2) Connally, E. F., Gevantmann, L. H., U. S. Naval Radiol. Defense Lab. USNRDL-ER-14 (1963). (3) Draganic, I. G.,J.Chim. Phys. 52, 595 (1955). (4) Ibid., J. Chim. Phys. 56, 9 (1959). (5) Draganić, I. G., Holm, N. W., Maul, J. E., Risö Report No. 22 (1961). (6) Draganić, I. G., Nucleonics 21 No. 2, 33-35 (1963). (7) Draganić, I. G., Radak, B. B., Marković, V. M., Intern. J. Appl. Radiation Isotopes 16, 145-152 (1965). (8) Draganić, I. G., Proc. Symp. Radiation Chem. 2nd, Budapest, Hungary, 1967. (9) Draganić, I. G., Sehested, K., Holm, N. W., Risö Report No. 112 (1967). (10) Draganić, Z. D., Draganić, I. G., Bull. Inst. Nucl.Sci."Boris Kidrich" (Belgrade) 7, No. 126 (1957). (11) Draganić, Z. D., Anal. Chim. Acta 28, 394 (1963). (12) Fenger, J., Risö Report No. 67 (1963). (13) Glass, A. L., AML Report No. NAEC-AML-1854 (1964). (14) Harmer, D., Dow Chemical Company, private communication ( 1964). (15) Holm, N. W., Bjergbakke, E., Sehested,K.,Draganić,I. G.,RisöReport No. 111 (1967). (16) Holm, N. W., Draganić, I. G. (in press). (17) Josimovic, Lj., Draganić, I., Sci. Paper I.P.C.R. Japan, 57, No. 1, 29-30 (1963). (18) Marković, V., Draganić, I. G., IBK Report (to be published)-and unpub lished results. (19) Matsui, M., Sci. Paper I.P.C.R. Japan 53, No. 1528 (1954). (20) Radak, B. B., Karapandzić, M., Gal, O., Nucleonics 22, No. 11, 52-54 (1964).


578

RADIATION CHEMISTRY

1

(21) Sehested, K., Bjergbakke, E., Holm, N. W., Proc. Symp. Radiation Chem. 2nd, Budapest, Hungary, pp. 149-160, 1967. (22) Weiss, J., HIRDL, Brookhaven National Laboratory, private communica tion (1964).


RECEIVED January 16, 1968.


The Oxalic Acid Dosimeter Procedure - ACS Publications

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