40 The Ferrous-Cupric Dosimeter E. BJERGBAKKE and K. SEHESTED
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Danish Atomic Energy Commission, Research Establishment Risö, Roskilde, Denmark
Air-free, air-saturated, and oxygenated solutions of the Fe +-Cu dosimeter have been investigated for Co and high dose-rate electron dosimetry. It has been shown that the dosage curves are not completely linear, but that an oxygenated or deaerated system may be used in the range 50 to 800 krad with an accuracy of 1%. The oxygenated system is for a 1.1 μsec. pulse independent of dose-rate up to 100 rads/pulse, and the deaerated solution up to 500 rads/pulse. 2
*T*he F e
2+
2 +
-Cu
60
2 +
dosimeter w a s suggested i n 1954 b y H a r t a n d W a l s h
( 5 ) , a n d t h e r e a c t i o n m e c h a n i s m has b e e n d e s c r i b e d b y H a r t (4). T h e range of t h e system (50-900 k r a d ) makes i t a u s e f u l p r o s p e c t i v e dosimeter—e.g., f o o d - p a s t e u r i z a t i o n processing—therefore, t h e system is of interest to m a n y people. A suggested A S T M p r o c e d u r e f o r testing at a n u m b e r of laboratories last year, a n d t h e present results h a v e b e e n a c c u m u l a t e d f o r the p u r p o s e of e v a l u a t i n g this p r o c e d u r e . A
Experimental Irradiations w e r e c a r r i e d o u t at the C o - g a m m a f a c i l i t y at R i s o (2) a n d at the 10 M e v . l i n e a r e l e c t r o n accelerator at R i s o ( J ) . A l l solutions w e r e i r r a d i a t e d i n 5 cc. borosilicate glass cells, fitted w i t h 5/20 s t a n d a r d taper joints. T h e m e t h o d o f e v a c u a t i o n , saturation, a n d filling is b e i n g d e s c r i b e d elsewhere b y Sehested et al. ( 7 ) . A t a l l g a m m a i r r a d i a t i o n s , doses w e r e d e t e r m i n e d w i t h the F r i c k e dosimeter u s i n g G p = 15.6. A t the electron i r r a d i a t i o n s , 10 vciM F e S 0 4 , 0 - s a t u r a t e d , 0.4M H S 0 (G *+ = 16.1), w h i c h is p r o v e n t o b e doserate i n d e p e n d e n t over t h e dose-rate range s t u d i e d ( 7 ) , w e r e u s e d f o r dose c a l i b r a t i o n . M e t h o d s a n d e q u i p m e n t f o r dose c a l i b r a t i o n at t h e electron i r r a d i a t i o n s are discussed i n d e t a i l elsewhere ( 7 ) . T h e dose h o m o g e n e i t y i n the i r r a d i a t i o n c e l l is estimated to b e better t h a n 2 5 % . T h e t e m p e r a t u r e range d u r i n g i r r a d i a t i o n s w a s 20° to 25°C. 6 0
e
2
s +
2
4
Fe
579 Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
580
RADIATION CHEMISTRY
1
T h e w a t e r w a s p u r i f i e d b y c o n v e n t i o n a l three-stage d i s t i l l a t i o n ( 3 ) . A l l glassware was c l e a n e d b y c o n v e n t i o n a l means a n d h e a t e d to 550 ° C . f o r 10 hours. T h e f o l l o w i n g reagents w e r e u s e d w i t h o u t f u r t h e r purification: (AnalaR) ( Merck, Analytical ) ( Merck, Analytical ) (Merck, Analytical)
H S0 CuS0 ,5H 0 FeS0 (NH ) S0 ,6H 0 3 0 % aqueous H 0 2
4
4
2
4
4
2
4
2
2
2
F e r r i c - i o n concentrations w e r e d e t e r m i n e d b y m e a s u r i n g o p t i c a l d e n sity at 3020 A . w i t h a C a r y 15 d u a l - b e a m spectrophotometer at 25 ° C .
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Experimental
Results
T h e effect of s u l f u r i c a c i d c o n c e n t r a t i o n o n the e x t i n c t i o n of ferrousf e r r i c sulfate solutions w i t h a n d w i t h o u t 10 m M C u S 0 F i g u r e l a . T h e results for f e r r i c sulfate w i t h o u t C u S 0 w i t h results r e p o r t e d b y H a y b i t t l e et al.
4
4
is s h o w n i n
is i n agreement
(6).
W h e n the o p t i c a l d e n s i t y is p l o t t e d against the sulfate
concentra
t i o n i n s t e a d of s u l f u r i c a c i d c o n c e n t r a t i o n , the curves for 1 m M C u S 0 , 4
1 m M f e r r i c - f e r r o u s sulfate, a n d 1 m M ferric-ferrous sulfate
become
parallel (Figure l b ) .
0.70
Optical Density
0.55
10"
10"
10"
Figure la.
Optical density as function of sulfuric-acid concentration Fe and F e /F e -Cu *-solutions 3+
Θ HSOi + lOmM CuSO, + ImM A HSQ + ImM Fe /Fe f
4
i+
2+
3+
2
Fe* /Fe +
s+
3+
Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
M/l
in
Fe / 2+
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40.
BJERBAKKE A N D SEHESTED
Figure
lb.
Ferrous-Cupric
Optical density as function of sulfate-ion concentration Fe and F e /F e -Cu -solutions 3+
2+
0 ESO>, + lOmM CuSO,, + ImM A H,SO + lmMFe' /Fe +
/t
3+
e
F e
2+
Fe /Fe i+
5+
1
in l O m M C u S 0 , 0.005M H S 0 4
The Fe
Fe /
s+
3 +
in 0.4M H S 0
= 2 1 9 7 M " c m . " ( 6 ) . U s i n g this v a l u e as a reference, 1
in
2+
T h e r e c o m m e n d e d e x t i n c t i o n coefficient f o r F e 3 +
581
Dosimeter
2
4
2
e H , a n d i n t h e 0 - s a t u r a t e d s o l u t i o n to H 0 + Ο Ι Ϊ 2
2
2
- » H 0 , w h i c h transfers a r e d u c i n g specie i n t o a n o x y g e n a t i n g specie.
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2
3
K)'
10'
1
Figure
3.
1
G *+ as function Fe
1 Dose rate 10 Krad/pulse
I 1
of dose-rate from a linear electron
accelerator
T h e r e l i a b i l i t y of t h e c o n v e n t i o n a l system 10 m M C u S 0 , 1 m M 4
F e S 0 , 10 m l V H S 0 4
2
4
as a d o s i m e t e r d e p e n d s o n t h e c o n c e n t r a t i o n o f
gases i n t h e s o l u t i o n . W e b e l i e v e that it is easier to p r e p a r e a n a d e q u a t e o x y g e n a t e d s o l u t i o n t h a n a c o m p l e t e l y d e a e r a t e d s o l u t i o n . W e therefore r e c o m m e n d u s i n g the o x y g e n a t e d system a n d i n c l u d i n g t h e f o l l o w i n g steps i n t h e p r o c e d u r e : (1) T h e oxygen concentration should be defined a n d reproducible —e.g., o x y g e n b u b b l i n g f o r 30 m i n u t e s . ( 2 ) T h e system s h o u l d b e c h e c k e d against the F r i c k e - d o s i m e t e r to p r o v e t h e a d e q u a c y of t h e o x y g e n a t i o n . (3) N e w solution should be made every d a y ( s i m p l y b y adding C u S Ô to a stock s o l u t i o n of 1 m M F e C 0 i n 10 mN H S 0 ). 4
4
2
4
Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
584
RADIATION CHEMISTRY
T h e advantages a n d a p p l i c a b i l i t y of t h e F e
2 +
-Cu
2 +
1
system m a y b e
s u m m a r i z e d as f o l l o w s : ( 1 ) T h e d o s i m e t e r c a n b e u s e d w i t h a n a c c u r a c y of 1 % i n t h e region 50-800 krad. (2)
T h e measurements i n v o l v e d are r a p i d , s i m p l e , a n d accurate.
( 3 ) T h e d o s i m e t e r is r a t h e r i n s e n s i t i v e to i m p u r i t i e s a n d s t a n d a r d sealed glass-ampules c a n b e u s e d as i r r a d i a t i o n cells. ( 4 ) T h e air-free F e - C u system is dose-rate i n d e p e n d e n t u p t o 500 rad//xsec. T h e 0 - s a t u r a t e d F e - C u system is dose-rate i n d e p e n d ent u p t o 100 rad/jusec. 2 +
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2 +
2 +
2
2 +
Literature Cited (1) Brynjolfsson, Α., Holm, N. W., Sehested, K., Thaarup, G., Proc., Ind. Uses of Large Radiation Sources, Vol. II, IAEA (1963), pp. 281-295. (2) Brynjolfsson, Α., Holm, N. W., Proc., Large Radiation Sources in Ind., IAEA (1960), pp. 115-120. (3) Fricke, H., Hart, E. J., "Radiation Dosimetry II," p. 167, Academic Press, Ν. Y., 1966. (4) Hart, E. J., Radiation Res. 2, 33 (1955). (5) Hart, E. J., Walsh, P. D., Radiation Res. 1, 342 (1954). (6) Haybittle, J. L., Saunders, R. D., Swallow, A. J., J. Chem. Phys. 25, 1213 (1956). (7) Sehested, K., Lang-Rasmussen, O., Fricke, H., J. Phys. Chem. 72, 626 (1968). RECEIVED January 23,
1968,
Hart; Radiation Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
