- Email: [email protected]
On the disintegration of 8.0 d 131I
Physica XVII, no 7
J u l i 1951
L E T T E R TO T H E EDITOR
On the disintegration of 8.0 d
131I
M a n y p a p e r s h a v e b e e n p u b l i s h e d o n t h e d i s i n t e g r a t i o n of 8.0 d 131I, b u t as y e t n o level s c h e m e h a s b e e n u n i v e r s a l l y a c c e p t e d . N o d i f f e r e n c e of o p i n i o n s e e m s t o e x i s t as t o t h e o c c u r r e n c e of t w o m a i n b e t a c o m p o n e n t s , o n e h a v i n g a n i n t e n s i t y of a b o u t 8 5 % a n d a m a x i m u m e n e r g y of a b o u t 600 keV, a n d t h e o t h e r h a v i n g a n i n t e n s i t y of a b o u t 15% a n d a m a x i m u m e n e r g y b e t w e e n 250 a n d 350 keV. Also, g a m m a t r a n s i t i o n s of 80, 284, 364 a n d 636 k e V h a v e c o m m o n l y b e e n f o u n d . I n a d d i t i o n a g a m m a t r a n s i t i o n of 163 k e y h a s b e e n d e t e c t e d , o r i g i n a t i n g f r o m a m e t a s t a b l e level i n 131Xe t h a t is fed b y a w e a k b e t a c o m p o n e n t of 807 k e V e n e r g y 4), 5), s), g). F u r t h e r , g a m m a r a y s of 177 k e V e) ~), a n d 724 k e V 7), s), 9) h a v e b e e n observed. T h e t h r e e level s c h e m e s t h a t h a v e b e e n p r o p o s e d h a v e b e e n d r a w n i n t h e i r e s s e n t i a l s i n fig. 1. I n all of t h e m t h e 364 keV g a m m a r a y is c o n s i d e r e d as a c r o s s o v e r t r a n s i t i o n of t h e 2 8 4 - - 8 0 k e V c a s c a d e , as follows f r o m t h e v e r y a c c u r a t e c u r v e d c r y s t a l g a m m a m e a s u r e m e n t s of L i n d e t al. 3). Metzger and DeutschX) s u g g e s t t h a t t h e 636 k e V g a m m a r a y l e a d s t o t h e g r o u n d s t a t e , w h e r e a s K e r n e t al. 2) f i n d a s o m e w h a t s m a l l e r m a x i m u m e n e r g y for t h e w e a k e r b e t a c o m p o n e n t , so t h a t i n t h e i r level s c h e m e t h e 636 k e V t r a n s i t i o n l e a d s t o t h e 80 keV level. T h e f o r m e r v i s i o n w a s s u p p o r t e d b y o u r o w n m e a s u r e m e n t s 9), b u t Z e 1 d e s e t al. s) c o n s i d e r t h e 724 k e V g a m m a t r a n s i t i o n ( a f t e r a s m a l l c o r r e c t i o n of t h e e n e r g y ) as a c r o s s o v e r t r a n s i t i o n of t h e 636 - - 80 keV cascade, so t h a t t h e y f a v o u r t h e l a t t e r vision. T h e t h i r d level scherne, p r o p o s e d b y C o r k e t al. ~) is b a s e d o n e n e r g y c o n s i d e r a t i o n s a l o n e a n d t h e a u t h o r s t h e m s e l v e s s t a t e t h a t i t does n o t s a t i s f y t h e o b s e r v e d r e l a t i v e i n t e n s i t i e s . A c a r e f u l r e e x a m i n a t i o n of o u r o w n m e a s u r e m e n t s h a s led t o t h e c o n c l u sion t h a t a n e n e r g y d i f f e r e n c e of 80 k e y b e t w e e n t h e K c o n v e r s i o n p e a k s of t h e 636 a n d t h e 724 k e V t r a n s i t i o n s w a s o u t s i d e o u r e x p e r i m e n t a l error. Also, t h e m a x i m u m l i m i t of t h e i n t e n s i t y of t h e 177 keV t r a n s i t i o n c a l c u l a t e d f r o m t h e m a x i m u m p o s s i b l e i n t e n s i t y of t h e K c o n v e r s i o n line i n o u r m e a s u r e m e n t s , a s s u m i n g electric dipole r a d i a t i o n , was o n l y 3 % , w h i c h rules o u t t h e level s c h e m e of C o r k e t al. Still, we t h o u g h t i t w o r t h - w h i l e t o h a v e a n i n d e p e n d e n t c h e c k o n t h e level s c h e m e b y m e a s u r i n g t h e a b s o r p t i o n of t h a t p a r t of t h e b e t a s p e c t r u m t h a t is in c o i n c i d e n c e w i t h t h e 80 keV t r a n s i t i o n . T h e r e f o r e a s o u r c e of 131I, s i m i l a r t o t h e ones u s e d in t h e m e a s u r e m e n t s of t h e b e t a s p e c t r u m w a s a t t a c h e d t o t h e b o t t o m p l a t e of o u r s p e c t r o m e t e r ( d e s c r i b e d in ref.0)). T h e s o u r c e h o l d e r was r e p l a c e d b y a s e c o n d geiger c o u n t e r w i t h a m i c a w i n d o w of 3.0 m g / c m 2. T h i s c o u n t e r was q u e n c h e d b y
-
-
6,58
-
-
ON T H E D I S I N T E G R A T I O N OF 8 . 0
d 13~I
659
a Den Hartog-Muller circuit similar to the one used for the s p e c t r o m e t e r . A n u m b e r of d i f f e r e n t a b s o r b e r s c o u l d b e p u t b e t w e e n t h e s o u r c e a n d t h e c o u n t e r b y m e a n s of t h e v a c u u m - s e a l e d a x l e of t h e b o t t o m g a t e c o n s t r u c t i o n . T h e s p e c t r o m e t e r w a s a d j u s t e d so as t o d e t e c t K s h e l l c o n v e r s i o n e l e c t r o n s of t h e 80 k e V t r a n s i t i o n . C o i n c i d e n c e s w e r e r e g i s t e r e d b y m e a n s of a c o n v e n t i o n a l c o i n c i d e n c e c i r c u i t w i t h a t i m e c o n s t a n t of 1.58 /~sec. A c o r r e c t i o n f o r t h e n u m b e r of c o i n c i d e n c e s d u e t o t h e b e t a spectrum focused together with the conversion line was found from the n u m b e r of c o i n c i d e n c e s r e g i s t e r e d w h e n t h e s p e c t r o m e t e r w a s a d j u s t e d Oil t h e b e t a s p e c t r u m b e s i d e t h e c o n v e r s i o n line, a n d t h e m e a s u r e m e n t s w i t h a b s o r b e r n o 5 (see t a b l e I) a l l o w e d a c o r r e c t i o n f o r c o i n c i d e n c e s d u e t o gamma and X-rays entering the bottom counter. TABLE I Absorbers used in the coincidence-absorption measurements of ~tI absorber i transmitted fraction of ~atI radiations no.
material
1 ] none 2 paper 3 paper 4 aluminium 5 lucite
i
thickness*)
f1300 keV fl 600 keV X 30 keV J7 > 80 keV I,A u25g ek erV el.
3mg/em = 11 ,, 19 ,, 37 ,, 344 ,,
0.85 0.49 0.27 0.05 0.00
I
0.97 0.85 0.75 0.52 0.00
!
1.0 1.0 1.0 1.0 0.9
I I
I i i
1.0 1.0 1.0 1.0 1.0
I I
!
0 0 0 0 0
*) inclusive of counter window (3 mg/cm z mica).
- 9,'okeV
636 [
91okeV
~
\#~1""
t1- I 80
~',,
80
1178 886
0
tO
20 30 absorber thickness
40 mg/cm2
Fig. 1. A b s o r p t i o n of t h e 1311 b e t a s p e c t r u m i n c o i n c i d e n c e w i t h K s h e l l c o n v e r s i o n e l e c t r o n s of t h e 80 k e V t r a n s i t i o n . T h e c u r v e s h a v e b e e n c a l c u l ated for the following level schemes: I: Metzger and Deutsch (ref. 1)) II:
III:
K e r net
Cork
al. (ref.
2))
e t al. (ref. r)).
660
O N T H E DISINTEGRATION OF 8.0 d 1311
T h e d i f f e r e n t a b s o r b e r s h a v e b e e n l i s t e d i n t a b l e I. T h e 300 k e V b e t a a b s o r p t i o n c u r v e w a s d e t e r m i n e d f r o m a n a b s o r p t i o n m e a s u r e m e n t of t h e 6°Co b e t a s p e c t r u m . I n fig. 1 t h e r e s u l t s of o u r m e a s u r e m e n t s h a v e b e e n p l o t t e d t o g e t h e r w i t h t h e c u r v e s for t h e d i f f e r e n t l e v e l s c h e m e s . All c u r v e s h a v e b e e n n o r m a l i z e d so as t o p a s s t h r o u g h t h e p o i n t a t zero a b s o r b e r . "Within t h e e x p e r i m e n t a l e r r o r t h e m e a s u r e d p o i n t s c o i n c i d e w i t h t h e c u r v e for t h e level s c h e m e of M e t z g e r and Deutsch, w h i l e t h e y c a n n o t e a s i l y be r e c o n c i l e d w i t h t h e o t h e r level s c h e m e s . G. ,J. NIJGH.
N. F. VERSTER. R. H. NUSSBAUM. R. VAN LIESHOUT
C. J. BAKKER. Instituut voor Kernphysisch Onderzoek, Zeema~-laboratorium, Amsterdam, Nederlaud Received 23-5-5 I.
REFERENCES 1) M e t z g e r , F. and D e u t s c h , M., Phys. Rev. 74 (1948)1640. 2) K e r n , B. D., M i t c h e l l , A. C. G and Z a f f a r a n o , D. J., Phys. Rev. 76 (1949) 94; 75 (1949) 1632. 3) L i n d , D.A., B r o w n , J . , K l e i n , D., M u l l e r , D. a n d D u M o n d , J.W. M., Phys. Rev. 75 (1949) 1544. 4) B r o s i , A. R., D e W i t t, T.W. and Z e l d e s , H., Phys. Rev. 75 (1949) 1615. 5) B e r g s t r S m , I., Phys. Rev. 80 (1950) ll4. 6) C o r k , J. M., K e l l e r , H. B., S a z . v n ~ k i , J., R u t l e d g e , W. C. and Stoddard, A. E., Phys. Rev. 75 (1949) 1621. 7) C o r k , J . M . , R u t l e d g e , W.C., S t o d d a r d , A. E., B r a n v a n , C. E. and C h i l d s , W. J., Phys. Rev. 81 (1951) 482. 8) Z e l d e s , H., B r o s i , A. R. and K e t e l l e , B. H., Phys. Rev. 81 (1951) 642. 9) V e r s t e r , N . F . , N i j g h , G . J . , v a n L i e s b o u t , R. and B a k k e r , C.J., Physica 17 (1951) 637.
J u l i 1951
L E T T E R TO T H E EDITOR
On the disintegration of 8.0 d
131I
M a n y p a p e r s h a v e b e e n p u b l i s h e d o n t h e d i s i n t e g r a t i o n of 8.0 d 131I, b u t as y e t n o level s c h e m e h a s b e e n u n i v e r s a l l y a c c e p t e d . N o d i f f e r e n c e of o p i n i o n s e e m s t o e x i s t as t o t h e o c c u r r e n c e of t w o m a i n b e t a c o m p o n e n t s , o n e h a v i n g a n i n t e n s i t y of a b o u t 8 5 % a n d a m a x i m u m e n e r g y of a b o u t 600 keV, a n d t h e o t h e r h a v i n g a n i n t e n s i t y of a b o u t 15% a n d a m a x i m u m e n e r g y b e t w e e n 250 a n d 350 keV. Also, g a m m a t r a n s i t i o n s of 80, 284, 364 a n d 636 k e V h a v e c o m m o n l y b e e n f o u n d . I n a d d i t i o n a g a m m a t r a n s i t i o n of 163 k e y h a s b e e n d e t e c t e d , o r i g i n a t i n g f r o m a m e t a s t a b l e level i n 131Xe t h a t is fed b y a w e a k b e t a c o m p o n e n t of 807 k e V e n e r g y 4), 5), s), g). F u r t h e r , g a m m a r a y s of 177 k e V e) ~), a n d 724 k e V 7), s), 9) h a v e b e e n observed. T h e t h r e e level s c h e m e s t h a t h a v e b e e n p r o p o s e d h a v e b e e n d r a w n i n t h e i r e s s e n t i a l s i n fig. 1. I n all of t h e m t h e 364 keV g a m m a r a y is c o n s i d e r e d as a c r o s s o v e r t r a n s i t i o n of t h e 2 8 4 - - 8 0 k e V c a s c a d e , as follows f r o m t h e v e r y a c c u r a t e c u r v e d c r y s t a l g a m m a m e a s u r e m e n t s of L i n d e t al. 3). Metzger and DeutschX) s u g g e s t t h a t t h e 636 k e V g a m m a r a y l e a d s t o t h e g r o u n d s t a t e , w h e r e a s K e r n e t al. 2) f i n d a s o m e w h a t s m a l l e r m a x i m u m e n e r g y for t h e w e a k e r b e t a c o m p o n e n t , so t h a t i n t h e i r level s c h e m e t h e 636 k e V t r a n s i t i o n l e a d s t o t h e 80 keV level. T h e f o r m e r v i s i o n w a s s u p p o r t e d b y o u r o w n m e a s u r e m e n t s 9), b u t Z e 1 d e s e t al. s) c o n s i d e r t h e 724 k e V g a m m a t r a n s i t i o n ( a f t e r a s m a l l c o r r e c t i o n of t h e e n e r g y ) as a c r o s s o v e r t r a n s i t i o n of t h e 636 - - 80 keV cascade, so t h a t t h e y f a v o u r t h e l a t t e r vision. T h e t h i r d level scherne, p r o p o s e d b y C o r k e t al. ~) is b a s e d o n e n e r g y c o n s i d e r a t i o n s a l o n e a n d t h e a u t h o r s t h e m s e l v e s s t a t e t h a t i t does n o t s a t i s f y t h e o b s e r v e d r e l a t i v e i n t e n s i t i e s . A c a r e f u l r e e x a m i n a t i o n of o u r o w n m e a s u r e m e n t s h a s led t o t h e c o n c l u sion t h a t a n e n e r g y d i f f e r e n c e of 80 k e y b e t w e e n t h e K c o n v e r s i o n p e a k s of t h e 636 a n d t h e 724 k e V t r a n s i t i o n s w a s o u t s i d e o u r e x p e r i m e n t a l error. Also, t h e m a x i m u m l i m i t of t h e i n t e n s i t y of t h e 177 keV t r a n s i t i o n c a l c u l a t e d f r o m t h e m a x i m u m p o s s i b l e i n t e n s i t y of t h e K c o n v e r s i o n line i n o u r m e a s u r e m e n t s , a s s u m i n g electric dipole r a d i a t i o n , was o n l y 3 % , w h i c h rules o u t t h e level s c h e m e of C o r k e t al. Still, we t h o u g h t i t w o r t h - w h i l e t o h a v e a n i n d e p e n d e n t c h e c k o n t h e level s c h e m e b y m e a s u r i n g t h e a b s o r p t i o n of t h a t p a r t of t h e b e t a s p e c t r u m t h a t is in c o i n c i d e n c e w i t h t h e 80 keV t r a n s i t i o n . T h e r e f o r e a s o u r c e of 131I, s i m i l a r t o t h e ones u s e d in t h e m e a s u r e m e n t s of t h e b e t a s p e c t r u m w a s a t t a c h e d t o t h e b o t t o m p l a t e of o u r s p e c t r o m e t e r ( d e s c r i b e d in ref.0)). T h e s o u r c e h o l d e r was r e p l a c e d b y a s e c o n d geiger c o u n t e r w i t h a m i c a w i n d o w of 3.0 m g / c m 2. T h i s c o u n t e r was q u e n c h e d b y
-
-
6,58
-
-
ON T H E D I S I N T E G R A T I O N OF 8 . 0
d 13~I
659
a Den Hartog-Muller circuit similar to the one used for the s p e c t r o m e t e r . A n u m b e r of d i f f e r e n t a b s o r b e r s c o u l d b e p u t b e t w e e n t h e s o u r c e a n d t h e c o u n t e r b y m e a n s of t h e v a c u u m - s e a l e d a x l e of t h e b o t t o m g a t e c o n s t r u c t i o n . T h e s p e c t r o m e t e r w a s a d j u s t e d so as t o d e t e c t K s h e l l c o n v e r s i o n e l e c t r o n s of t h e 80 k e V t r a n s i t i o n . C o i n c i d e n c e s w e r e r e g i s t e r e d b y m e a n s of a c o n v e n t i o n a l c o i n c i d e n c e c i r c u i t w i t h a t i m e c o n s t a n t of 1.58 /~sec. A c o r r e c t i o n f o r t h e n u m b e r of c o i n c i d e n c e s d u e t o t h e b e t a spectrum focused together with the conversion line was found from the n u m b e r of c o i n c i d e n c e s r e g i s t e r e d w h e n t h e s p e c t r o m e t e r w a s a d j u s t e d Oil t h e b e t a s p e c t r u m b e s i d e t h e c o n v e r s i o n line, a n d t h e m e a s u r e m e n t s w i t h a b s o r b e r n o 5 (see t a b l e I) a l l o w e d a c o r r e c t i o n f o r c o i n c i d e n c e s d u e t o gamma and X-rays entering the bottom counter. TABLE I Absorbers used in the coincidence-absorption measurements of ~tI absorber i transmitted fraction of ~atI radiations no.
material
1 ] none 2 paper 3 paper 4 aluminium 5 lucite
i
thickness*)
f1300 keV fl 600 keV X 30 keV J7 > 80 keV I,A u25g ek erV el.
3mg/em = 11 ,, 19 ,, 37 ,, 344 ,,
0.85 0.49 0.27 0.05 0.00
I
0.97 0.85 0.75 0.52 0.00
!
1.0 1.0 1.0 1.0 0.9
I I
I i i
1.0 1.0 1.0 1.0 1.0
I I
!
0 0 0 0 0
*) inclusive of counter window (3 mg/cm z mica).
- 9,'okeV
636 [
91okeV
~
\#~1""
t1- I 80
~',,
80
1178 886
0
tO
20 30 absorber thickness
40 mg/cm2
Fig. 1. A b s o r p t i o n of t h e 1311 b e t a s p e c t r u m i n c o i n c i d e n c e w i t h K s h e l l c o n v e r s i o n e l e c t r o n s of t h e 80 k e V t r a n s i t i o n . T h e c u r v e s h a v e b e e n c a l c u l ated for the following level schemes: I: Metzger and Deutsch (ref. 1)) II:
III:
K e r net
Cork
al. (ref.
2))
e t al. (ref. r)).
660
O N T H E DISINTEGRATION OF 8.0 d 1311
T h e d i f f e r e n t a b s o r b e r s h a v e b e e n l i s t e d i n t a b l e I. T h e 300 k e V b e t a a b s o r p t i o n c u r v e w a s d e t e r m i n e d f r o m a n a b s o r p t i o n m e a s u r e m e n t of t h e 6°Co b e t a s p e c t r u m . I n fig. 1 t h e r e s u l t s of o u r m e a s u r e m e n t s h a v e b e e n p l o t t e d t o g e t h e r w i t h t h e c u r v e s for t h e d i f f e r e n t l e v e l s c h e m e s . All c u r v e s h a v e b e e n n o r m a l i z e d so as t o p a s s t h r o u g h t h e p o i n t a t zero a b s o r b e r . "Within t h e e x p e r i m e n t a l e r r o r t h e m e a s u r e d p o i n t s c o i n c i d e w i t h t h e c u r v e for t h e level s c h e m e of M e t z g e r and Deutsch, w h i l e t h e y c a n n o t e a s i l y be r e c o n c i l e d w i t h t h e o t h e r level s c h e m e s . G. ,J. NIJGH.
N. F. VERSTER. R. H. NUSSBAUM. R. VAN LIESHOUT
C. J. BAKKER. Instituut voor Kernphysisch Onderzoek, Zeema~-laboratorium, Amsterdam, Nederlaud Received 23-5-5 I.
REFERENCES 1) M e t z g e r , F. and D e u t s c h , M., Phys. Rev. 74 (1948)1640. 2) K e r n , B. D., M i t c h e l l , A. C. G and Z a f f a r a n o , D. J., Phys. Rev. 76 (1949) 94; 75 (1949) 1632. 3) L i n d , D.A., B r o w n , J . , K l e i n , D., M u l l e r , D. a n d D u M o n d , J.W. M., Phys. Rev. 75 (1949) 1544. 4) B r o s i , A. R., D e W i t t, T.W. and Z e l d e s , H., Phys. Rev. 75 (1949) 1615. 5) B e r g s t r S m , I., Phys. Rev. 80 (1950) ll4. 6) C o r k , J. M., K e l l e r , H. B., S a z . v n ~ k i , J., R u t l e d g e , W. C. and Stoddard, A. E., Phys. Rev. 75 (1949) 1621. 7) C o r k , J . M . , R u t l e d g e , W.C., S t o d d a r d , A. E., B r a n v a n , C. E. and C h i l d s , W. J., Phys. Rev. 81 (1951) 482. 8) Z e l d e s , H., B r o s i , A. R. and K e t e l l e , B. H., Phys. Rev. 81 (1951) 642. 9) V e r s t e r , N . F . , N i j g h , G . J . , v a n L i e s b o u t , R. and B a k k e r , C.J., Physica 17 (1951) 637.