Nuclear Decay Data - ACS Symposium Series (ACS Publications)

14 Nuclear Decay Data An Important Interface Between Basic and Applied Science

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on February 28, 2016 | http://pubs.acs.org Publication Date: November 14, 1986 | doi: 10.1021/bk-1986-0324.ch014

C. W. Reich Idaho National Engineering Laboratory, EG&G Idaho, Inc., Idaho Falls, ID 83415 In this paper, we discuss several categories of decay data which have contributed to low-energy nuclear physics, indicate some of the ways they are useful in solving problems in other areas and identify needs for further measurements. Illustrations include half-life and emission-probability data of actinide nuclides important for reactor technology and useful as reference standards for nuclear-data measurements. Decay data of highly neutron-rich fission-product nuclides are important in such diverse areas as astrophysics and reactor-safety research. Some of these data needs and experimental approaches suitable for satisfying them are presented. 1.

Introduction

Data on t h e decay p r o p e r t i e s ( e . g . , t o t a l and p a r t i a l h a l f - l i v e s , t o t a l decay e n e r g i e s , e n e r g i e s and e m i s s i o n p r o b a b i l i t i e s o f t h e e m i t t e d r a d i a t i o n s ) have i n t h e p a s t made m a j o r c o n t r i b u t i o n s t o o u r knowledge o f n u c l e a r p r o p e r t i e s a t low e x c i t a t i o n e n e r g i e s and o f t h e v a r i o u s modes o f m o t i o n t h a t g i v e r i s e t o them. E v i d e n c e t h a t t h e s e d a t a c o n t i n u e t o have a s i g n i f i c a n t i n f l u e n c e on t h i s f i e l d , and i n d e e d o f t h e c o n t i n u i n g v i t a l i t y o f t h e f i e l d i t s e l f , i s p r o v i d e d by t h e l a r g e number and b r e a d t h o f c o n t e n t o f t h e p a p e r s b e i n g p r e s e n t e d a t t h i s symposium. Beyond t h i s h i g h l y i n t e r e s t i n g , b u t r e l a t i v e l y r e s t r i c t e d a p p l i c a t i o n , h o w e v e r , n u c l e a r decay d a t a p l a y an i m p o r t a n t r o l e i n many o t h e r a r e a s o f b a s i c and a p p l i e d s c i e n c e . I n any d i s c u s s i o n o f decay d a t a and t h e i r a p p l i c a t i o n s , t h e f o l l o w i n g s h o u l d be k e p t i n m i n d . I n s p i t e o f t h e i r wide a p p l i c a b i l i t y , t h e p r i m a r y m o t i v a t i o n f o r t h e i r measurement has l a r g e l y been t h e i n f o r m a t i o n w h i c h t h e y provide f o r low-energy nuclear physics. The e x t e n s i v e measurement a c t i v i t y i n t h i s a r e a o v e r t h e p a s t t h r e e decades o r so has p r o d u c e d a l a r g e amount o f f a i r l y d e t a i l e d d a t a on t h e decay p r o p e r t i e s o f u n s t a b l e n u c l e i . However, because o f t h e i n t e r e s t s and o b j e c t i v e s o f most o f t h e m e a s u r e r s o f t h e s e d a t a , t h e e x i s t e n c e o f t h i s e x t e n s i v e body o f i n f o r m a t i o n does n o t n e c e s s a r i l y mean t h a t t h e d e c a y - d a t a needs o f any g i v e n a r e a a r e s a t i s f i e d . Such needs f r e q u e n t l y a r e h i g h l y s p e c i a l i z e d and r e q u i r e a d d i t i o n a l c h a r a c t e r i s t i c s n o t u s u a l l y c o n s i d e r e d by an e x p e r i m e n t e r whose i n t e r e s t s l i e in other areas. To s a t i s f y such n e e d s , s p e c i a l i z e d measurements, occasionally u t i l i z i n g techniques s p e c i f i c a l l y t a i l o r e d t o the p a r t i c u l a r a p p l i c a t i o n , are r e q u i r e d . As a r e s u l t , t h e f i e l d o f d e c a y - d a t a measurement, a l t h o u g h by many s t a n d a r d s a m a t u r e o n e , c o n t i n u e s t o p r e s e n t e x c i t i n g new c h a l l e n g e s as e x p e r i m e n t a l c a p a b i l i t i e s d e v e l o p and a d d i t i o n a l needs i n o t h e r a r e a s o f b a s i c and a p p l i e d s c i e n c e c o n t i n u e t o be i d e n t i f i e d . 0097-6156/ 86/ 0324-0094S06.00/ 0 © 1986 American Chemical Society

In Nuclei Off the Line of Stability; Meyer, Richard A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

14.

REICH

95

Nuclear Decay Data

To a d e q u a t e l y t r e a t t h e s e many a p p l i c a t i o n s and t o i l l u s t r a t e t h e s p e c i f i c ways i n w h i c h decay d a t a make u s e f u l , i f n o t c r u c i a l , c o n t r i b u t i o n s t o them i s a t a s k t h a t l i e s beyond t h e space and t i m e l i m i t a t i o n s o f t h i s paper. We have t h u s chosen t o l i m i t t h e scope o f t h i s p r e s e n t a t i o n t o t h e d i s c u s s i o n o f s e v e r a l s e l e c t e d e x a m p l e s , drawn m o s t l y f r o m t h e a r e a o f fission-reactor physics. These i n c l u d e t h e r e s u l t s o f r e c e n t s i g n i f i c a n t d e v e l o p m e n t s i n a c t i n i d e - n u c l i d e decay d a t a a n d , i n t h e s p i r i t o f t h i s symposium, decay d a t a o f f i s s i o n - p r o d u c t n u c l i d e s o f f t h e l i n e o f β s t a b i l i t y and some o f t h e p r o b l e m s and c h a l l e n g e s t h e y p r e s e n t t o b o t h e x p e r i m e n t a l c a p a b i l i t i e s and n u c l e a r t h e o r y .


2.

An I n t e r n a t i o n a l C o o r d i n a t e d Program o f A c t i n i d e - N u c l i d e Measurement and E v a l u a t i o n

Decay-Data

I n 1975, t h e IAEA convened an A d v i s o r y Group M e e t i n g on T r a n s a c t i n i u m I s o t o p e N u c l e a r Data a t K a r l s r u h e , F.R.G. [TND76] t o s u r v e y t h e r e q u i r e m e n t s f o r and s t a t u s o f t r a n s a c t i n i u m i s o t o p e n u c l e a r d a t a r e l e v a n t t o f i s s i o n r e a c t o r r e s e a r c h and t e c h n o l o g y . I t was f o u n d t h a t t h e a c c u r a c y o f many o f t h e decay d a t a was n o t s u f f i c i e n t t o s a t i s f y a number o f t h e needs f o r such a p p l i c a t i o n s as m a t e r i a l s s a f e g u a r d s , f u e l a s s a y , sample-mass d e t e r m i n a t i o n and s t a n d a r d s p r e p a r a t i o n . One o f t h e recommendations drawn up a t t h i s m e e t i n g c a l l e d f o r an i n t e r n a t i o n a l l y c o o r d i n a t e d program o f d e c a y - d a t a measurement and e v a l u a t i o n t o a d d r e s s t h i s s i t u a t i o n . Subsequently, in 1 9 7 7 , t h e IAEA o r g a n i z e d a C o o r d i n a t e d Research Program (CRP) t o measure and e v a l u a t e decay d a t a f o r s e l e c t e d t r a n s a c t i n i u m n u c l i d e s . Research g r o u p s f r o m f i v e l a b o r a t o r i e s a r o u n d t h e w o r l d a g r e e d t o p a r t i c i p a t e i n t h i s CRP; and work g o t underway i n t h e S p r i n g o f 1978. The work o f t h i s CRP has r e c e n t l y c o n c l u d e d and a r e p o r t s u m m a r i z i n g t h e r e s u l t s o f t h i s t a s k has been p r e p a r e d . New, h i g h l y p r e c i s e decay d a t a on t o t a l and/or p a r t i a l h a l f - l i v e s f o r 7 n u c l i d e s , α - p a r t i c l e emission p r o b a b i l i t i e s ( P a ) f o r 7 n u c l i d e s , and γ - r a y e m i s s i o n p r o b a b i l i t i e s ( Ρ γ ) f o r 21 n u c l i d e s have been p r o d u c e d . The f i n a l l i s t o f recommended decay d a t a i n c l u d e s t h e s e r e s u l t s , as w e l l as t h o s e f r o m o t h e r r e c e n t measurements, t o g e t h e r w i t h c a r e f u l l y e v a l u a t e d i n f o r m a t i o n on a number o f other nuclides. I n a l l , t h i s l i s t i n c l u d e s h a l f - l i f e v a l u e s f o r 125 n u c l i d e s a n d , f o r t h e more p r o m i n e n t t r a n s i t i o n s o n l y , P a v a l u e s f o r 30 n u c l i d e s and Ργ v a l u e s f o r 47 n u c l i d e s . [Some o f t h e s e d a t a r e p r e s e n t simply the r e s u l t s of previously published e v a l u a t i o n s . ] These d a t a w i l l be i n c l u d e d i n t h e f i n a l r e p o r t o f t h e CRP, t o be p u b l i s h e d as one o f t h e IAEA Technical Reports S e r i e s . One example o f t h e improvement i n t h e q u a l i t y o f t h e d a t a r e s u l t i n g f r o m t h i s measurement program i s p r o v i d e d by t h e Ργ v a l u e s f o r U. These d a t a were measured by t h r e e o f t h e CRP p a r t i c i p a n t s . When combined w i t h a n o t h e r r e c e n t measurement, t h e s e l e d t o a recommended Ργ v a l u e o f 5 7 . 2 + 0 . 5 p h o t o n s / 1 0 0 decays f o r t h e p r o m i n e n t 1 8 5 . 7 - k e V γ r a y . The p r e v i o u s l y a c c e p t e d v a l u e [NDS77, T 0 I 7 8 ] f o r t h i s q u a n t i t y was 5 4 . , w i t h no u n c e r t a i n t y g i v e n . 2 3 5

3.

Actinide Half-Lives

as S t a n d a r d s f o r

N u c l e a r Data Measurements

A knowledge o f t h e h a l f - l i f e i s r e q u i r e d f o r any a p p l i c a t i o n i n w h i c h q u a n t i t a t i v e assay o f m a t e r i a l f o r r a d i o n u c l i d e c o n t e n t i s d e s i r e d . In f i s s i o n - r e a c t o r r e s e a r c h and t e c h n o l o g y , f o r e x a m p l e , a c c u r a t e h a l f - l i f e


96

NUCLEI OFF THE LINE OF STABILITY

d a t a a r e r e q u i r e d f o r many a r e a s r e l a t e d t o t h e s a f e g u a r d i n g o f s p e c i a l nuclear m a t e r i a l s . I n t h e p r e c i s e measurement o f n e u t r o n - i n d u c e d r e a c t i o n c r o s s s e c t i o n s i m p o r t a n t f o r s t u d i e s o f f a s t - r e a c t o r f u e l c y c l e s , such i n f o r m a t i o n i s n e c e s s a r y f o r t h e a c c u r a t e mass assay o f , and t h e c o r r e c t i o n f o r n u c l i d e decay i n , t h e samples u t i l i z e d . I n r e c o g n i t i o n o f t h e s e n e e d s , a l i s t o f recommended h a l f - l i f e v a l u e s f o r a number o f a c t i n i d e n u c l i d e s u s e f u l as s t a n d a r d s f o r n u c l e a r - d a t a measurements was p r e p a r e d s e v e r a l y e a r s ago [ V A N 8 3 ] . T h i s l i s t i n c l u d e d b o t h t o t a l and p a r t i a l h a l f - l i f e d a t a f o r 11 such n u c l i d e s - t h e i m p o r t a n t i s o t o p e s o f U, Np and P u , as w e l l as Cf. S u b s e q u e n t l y , t h e s e d a t a were r e v i s e d [ R E I 8 5 a ] t o i n c o r p o r a t e t h e r e s u l t s o f new measurements, some o f them f r o m t h e work o f t h e CRP. These d a t a a r e g i v e n i n a r e c e n t paper [ R E I 8 5 b ] , as w e l l as i n t h e f i n a l r e p o r t o f t h e IAEA CRP.


2 5 2

I m p o r t a n t comments r e g a r d i n g some o f t h e s e v a l u e s need t o be made. For e x a m p l e , t h e p r e s e n t l y recommended h a l f - l i f e v a l u e s f o r N p and Cf a r e , r e s p e c t i v e l y , ( 2 . 1 4 ± 0 . 0 1 ) x l 0 y and ( 2 . 6 4 5 + 0 . 0 0 8 ) y . Although the q u o t e d p r e c i s i o n o f t h e f o r m e r i s q u i t e good ( M ) . 5 % ) , t h i s v a l u e i s based on t h e r e s u l t s o f o n l y one measurement. Some e v i d e n c e t h a t i t may be s i g n i f i c a n t l y i n e r r o r has been g i v e n by [MEA83], who f i n d s t h a t h i s measured r a t i o o f t h e N p f i s s i o n cross section to t h a t of U in the MeV r e g i o n o f n e u t r o n e n e r g i e s d i f f e r s f r o m t h o s e o f o t h e r e x p e r i m e n t e r s who used d i f f e r e n t t e c h n i q u e s . One p o t e n t i a l s o u r c e o f t h i s d i s c r e p a n c y i s t h e mass assay o f t h e N p s a m p l e s , w h i c h depends u l t i m a t e l y on t h e v a l u e used f o r t h e Np half-life. A satisfactory resolution of this d i s c r e p a n c y w o u l d h e l p s u p p o r t t h e use o f ' N p as a n e u t r o n f l u x s t a n d a r d i n t h e MeV r e g i o n . Regarding the C f h a l f - l i f e , [SMI83] r e p o r t s i n a recent analysis t h a t the present s i t u a t i o n i s confused. The r e s u l t s o f t e n measurements r e p o r t e d w i t h h i g h p r e c i s i o n s ( r a n g i n g f r o m M).4% t o ^0.04%) o v e r t h e p a s t t w e n t y y e a r s , t e n d t o c l u s t e r a r o u n d two d i s t i n c t v a l u e s , v i z . 2 . 6 3 8 y and 2 . 6 5 1 y . Evidence e x i s t s which p r o v i d e s s u p p o r t f o r each o f t h e s e , and i t i s t h u s n o t c l e a r w h i c h ( i f i n d e e d e i t h e r ) o f them represents the " c o r r e c t " Cf half-life. 2 3 7

2 5 2

6

2 3 7

2 3 5

2 3 7

2 3 7

2 3

2 5 2

2 5 2

The s t a t u s o f t h e s e v a l u e s emphasizes t h e i m p o r t a n c e o f t h e o b s e r v a t i o n t h a t s i m p l y because d a t a e x i s t whose q u o t e d p r e c i s i o n i s q u i t e a d e q u a t e f o r c e r t a i n ( i n d e e d many) p u r p o s e s i t c a n n o t be assumed t h a t t h e r e i s no need f o r f u r t h e r measurements. W h i l e i t i s h i g h l y u n l i k e l y t h a t any changes i n t h e s e two h a l f - l i f e v a l u e s w h i c h r e s u l t f r o m t h e e v e n t u a l r e s o l u t i o n o f these above-mentioned d i s c r e p a n c i e s w i l l s i g n i f i c a n t l y a f f e c t basic nuclear p h y s i c s , t h e s e d i s c r e p a n c i e s n o n e t h e l e s s p r e s e n t s e r i o u s p r o b l e m s f o r many r e a c t o r - r e l a t e d nuclear-measurement e f f o r t s . 4.

S h o r t - L i v e d F i s s i o n - P r o d u c t Decay Data

Because o f t h e i r i n t i m a t e l i n k w i t h e n e r g y p r o d u c t i o n i n n u c l e a r r e a c t o r s , f i s s i o n p r o d u c t s and t h e i r n u c l e a r d a t a have l o n g o c c u p i e d an important position in reactor technology. In recent years, i n t e r e s t in s h o r t - l i v e d f i s s i o n - p r o d u c t decay d a t a has i n c r e a s e d m a r k e d l y , as t h e i r r e l e v a n c e t o d i f f e r e n t a r e a s o f r e s e a r c h and t e c h n o l o g y has become r e c o g n i z e d . In a d d i t i o n t o t h e i r importance f o r e s t i m a t i o n o f the f i s s i o n - p r o d u c t decayheat source term i n nuclear r e a c t o r s , the i n c r e a s i n g a t t e n t i o n being focused on t h e assessment o f t h e h a z a r d s a s s o c i a t e d w i t h t h e r e l e a s e , t r a n s p o r t and


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Nuclear Decay Data

97


d e p o s i t i o n o f f i s s i o n p r o d u c t s f o l l o w i n g p o s t u l a t e d r e a c t o r a c c i d e n t s has p r o d u c e d a need f o r a d d i t i o n a l i n f o r m a t i o n on t h e i r e n e r g y s p e c t r a , e s p e c i a l l y f o r the isotopes o f the v o l a t i l e elements. In astrophysics there i s a need [MAT84] f o r d a t a on t h e h i g h l y n e u t r o n - r i c h f i s s i o n - p r o d u c t n u c l i d e s t o h e l p r e f i n e and f u r t h e r c o n s t r a i n p r e s e n t models o f e l e m e n t a l synthesis in s t e l l a r environments. In the analysis o f recent experiments a t n u c l e a r r e a c t o r s [B0E84] t o s e a r c h f o r n e u t r i n o o s c i l l a t i o n s , a knowledge o f the r e a c t o r a n t i n e u t r i n o spectrum, e s p e c i a l l y the high-energy region (which depends s e n s i t i v e l y on t h e decay p r o p e r t i e s o f t h e s h o r t - l i v e d f i s s i o n p r o d u c t s ) , i s needed. I n a d d i t i o n t o t h e d i f f i c u l t i e s i n p r o d u c i n g good s a m p l e s , t h e s t u d y o f s h o r t - l i v e d f i s s i o n - p r o d u c t decay schemes p r e s e n t s s p e c i a l p r o b l e m s . Because o f t h e c o m p l e x i t y o f t h e s p e c t r u m o f t h e e m i t t e d r a d i a t i o n and t h e l a r g e number o f e n e r g y l e v e l s t h a t can be p o p u l a t e d , t h e o b s e r v a t i o n o f a l l t h e γ - r a y t r a n s i t i o n s and t h e c o r r e c t p l a c e m e n t o f them w i t h i n t h e d a u g h t e r - n u c l e u s l e v e l scheme i s a d i f f i c u l t and e x t r e m e l y t i m e - c o n s u m i n g p r o c e s s , i f i t i s indeed p o s s i b l e a t a l l . Consequently, i n actual p r a c t i c e , i t i s almost never done. For most p u r p o s e s i n l o w - e n e r g y n u c l e a r p h y s i c s t h i s i s not a serious problem, since i t i s usually only the level properties i n t h e f i r s t MeV o r two o f e x c i t a t i o n t h a t a r e o f i n t e r e s t , and t h e s e can be o b t a i n e d w i t h c o n s i d e r a b l e c o n f i d e n c e f r o m even a r e l a t i v e l y i n c o m p l e t e decay scheme. I n cases where an a c c u r a t e knowledge o f how t h e e m i t t e d e n e r g y i s d i s t r i b u t e d , h o w e v e r , t h e l a c k o f a c o m p l e t e decay scheme can be a fundamental l i m i t a t i o n . A simole i l l u s t r a t i o n o f t h i s , discussed in [ R E I 8 5 b ] , i s p r o v i d e d by t h e ° B r decay ( T w ? = 5 5 . 7 s ) . A r e c e n t v e r y d e t a i l e d s t u d y [RAM83] has l e d t o a deduced d i s t r i b u t i o n o f t h e β i n t e n s i t y feeding the l e v e l s i n the ° K r daughter t h a t i s q u i t e d i f f e r e n t from t h a t i n [NDS79]. [RAM83] a l s o r e p o r t Ργ v a l u e s ^30% s m a l l e r t h a n those i n [NDS79]. These d i f f e r e n c e s i n t h e p r o p o s e d decay scheme l e a d t o s i g n i f i c a n t l y d i f f e r e n t v a l u e s f o r t h e a v e r a g e e n e r g i e s p e r decay ( i m p o r t a n t f o r r e a c t o r d e c a y - h e a t a s s e s s m e n t ) , as shown i n T a b l e 1 . 7

7

The B r decay has a number of simplifying features [ R E I 8 5 b ] , w h i c h make i t s s t u d y s i m p l e r t h a n t h o s e o f most o f the s h o r t - l i v e d f i s s i o n products. S i n c e , even f o r t h i s Quantity [RAM83] ÇNDS79] " s i m p l e " case ( w h i c h even so took several years to 1643. 1861. complete), a d e t a i l e d study 2122. 2358. o r o d u c e d such d r a s t i c changes 3204. 4113. i n many o f t h e deduced decay sum* 6969. 8332. p r o p e r t i e s , c a u t i o n s h o u l d be taken i n using p r e s e n t l y For a " p e r f e c t " i n t e n s i t y b a l a n c e , t h e a v a i l a b l e d a t a on such t h r e e a v e r a g e - e n e r g y v a l u e s s h o u l d sum n u c l i d e s f o r many a p p l i c a t i o n s . t o Qg(=6830 + 1 2 0 ) . I t seems l i k e l y , [ R E I 8 5 b ] , f o r e x a m p l e , t h a t t h e somewhat p o o r e r p r e d i c t i o n o f t h e β- and γ - r a y components o f t h e d e c a y - h e a t s o u r c e t e r m u s i n g t h e ENDF/B-V decay d a t a t h a n was o b t a i n e d u s i n g ENDF/B-IV r e s u l t e d f r o m t h e i n c l u s i o n i n t h e f o r m e r o f decay d a t a f o r a number o f s h o r t - l i v e d f i s s i o n p r o d u c t s t h a t were o b t a i n e d f r o m j u s t such i n c o m p l e t e l y d e t e r m i n e d decay schemes. Table 1 Comparison o f a v e r a g e d e c a y - e n e r g y v a l u e s ( i n keV) f o r B r deduced f r o m two d i f f e r e n t s e t s o f d a t a

8 7

8 7


98

NUCLEI OFF THE LINE OF STABILITY


Many o f t h e a p p l i c a t i o n s , p a r t i c u l a r l y t h e more c h a l l e n g i n g o n e s , o f f i s s i o n - p r o d u c t decay d a t a have i n v o l v e d t h e f i s s i o n p r o d u c t s as a g r o u p . Because o f t h e i r l a r g e number (>700) and t h e f a c t t h a t a l m o s t no d a t a have been a v a i l a b l e f o r many o f t h e m , i t has a l w a y s been n e c e s s a r y f o r such a p p l i c a t i o n s t o u t i l i z e c a l c u l a t e d v a l u e s f o r t h e unmeasured q u a n t i t i e s . To do t h i s , a number o f d i f f e r e n t approaches have been t a k e n t o d e s c r i b e t h e β-decay p r o p e r t i e s ( β - s t r e n g t h f u n c t i o n s ) o f t h e s e n u c l i d e s [TAK72, MAN82, K L A 8 3 ] . The most c o m p r e h e n s i v e o f t h e s e approaches has been t h a t o f K l a p d o r and h i s c o - w o r k e r s [KLA83] who, u s i n g a s p e c i f i c model f o r t h e β - s t r e n g t h f u n c t i o n , p r o v i d e p r e d i c t i o n s f o r a wide v a r i e t y o f f i s s i o n - p r o d u c t - r e l a t e d phenomena i n a s t r o p h y s i c s and n u c l e a r p h y s i c s . These d i f f e r e n t approaches g i v e d i f f e r e n t p r e d i c t i o n s f o r many o f t h e phenomena o f i n t e r e s t ; and i f one i s t o a p p l y them w i t h some degree o f c o n f i d e n c e t o t h e s o l u t i o n o f a w i d e range o f p r o b l e m s , i t i s n e c e s s a r y t o e s t a b l i s h which approaches, or which aspects o f the d i f f e r e n t approaches, a r e r e l i a b l e and w h i c h a r e n o t . T h i s i s n o t always a simple m a t t e r . Part o f t h e p r o b l e m i n a s s e s s i n g t h e v a r i o u s t h e o r e t i c a l approaches r e s u l t s f r o m the complexity o f the s i t u a t i o n . I n d i f f e r e n t a p p l i c a t i o n s , one i s r e a l l y t e s t i n g d i f f e r e n t a g g r e g a t e s o f v a r i o u s t y p e s o f d a t a ( f i s s i o n y i e l d s , Q$ v a l u e s , a v e r a g e decay e n e r g i e s , e t c . ) ; and i t i s d i f f i c u l t t o i s o l a t e t h e e f f e c t o f any one i n d i v i d u a l component. To p e r m i t r e l i a b l e p r e d i c t i o n s o f phenomena r e l a t e d t o t h e decay p r o p e r t i e s o f f i s s i o n p r o d u c t s as a g r o u p , a more s y s t e m a t i c a p p r o a c h i s r e q u i r e d . Based on p a s t e x p e r i e n c e , t h e o u t l i n e s o f such an a p p r o a c h a r e c l e a r . Both t h e o r y and e x p e r i m e n t , i n c l o s e c o l l a b o r a t i o n , a r e needed t o r e f i n e t h e models used t o c a l c u l a t e t h e β-decay p r o p e r t i e s o f t h e i n d i v i d u a l n u c l i d e s . On t h e t h e o r e t i c a l s i d e , a number o f i n t e r e s t i n g f e a t u r e s a r e b e g i n n i n g t o emerge. U s i n g a model o f t h e β - s t r e n g t h f u n c t i o n r e c e n t l y d e v e l o p e d by [ K R U 8 4 ] , [KRA85] has c a l c u l a t e d t h e decay p r o p e r t i e s o f a number o f n u c l i d e s . From t h e s e r e s u l t s , he r e a c h e s t h e f o l l o w i n g c o n c l u s i o n s . Because o f n u c l e a r s t r u c t u r e e f f e c t s , t h e r e i s no s i m p l e , g l o b a l β - s t r e n g t h f u n c t i o n s y s t e m a t i c s t h a t i s s e n s i t i v e enough t o p e r m i t r e l i a b l e e x t r a p o l a t i o n s . In g e n e r a l , deformation e f f e c t s in the f a r unstable nuclei tend to s h i f t the β s t r e n g t h down, r e s u l t i n g i n l a r g e r v a l u e s and s m a l l e r v a l u e s as compared t o s p h e r i c a l n u c l i d e s w i t h t h e same Q$ v a l u e . Perhaps most i m p o r t a n t , no s h e l l model a p p e a r s c a p a b l e o f p r o v i d i n g r e l i a b l e βs t r e n g t h p r e d i c t i o n s o v e r t h e w h o l e mass range w i t h o n l y one p a r a m e t e r s e t . E x p e r i m e n t a l l y , t h e measurements must be t a i l o r e d s p e c i f i c a l l y t o p r o d u c e t h a t i n f o r m a t i o n most s e n s i t i v e t o r e f i n i n g t h e t h e o r e t i c a l concepts. Because i t i s n o t f e a s i b l e t o measure a]J_ t h e n u c l i d e s , o n l y t h o s e whose i n f o r m a t i o n i s t h e most i m p o r t a n t s h o u l d be s t u d i e d . C o n v e n t i o n a l decay-schemes s t u d i e s do n o t seem a p p r o p r i a t e , because o f t h e c o m p l e x i t y o f t h e decay schemes, t h e e r r o r s t o w h i c h t h e y a r e s u b j e c t ( c f . the discussion o f B r above) and t h e l a r g e amount o f t i m e needed t o c a r r y them o u t . D i r e c t measurement o f t h e β - s t r e n g t h f u n c t i o n s t h e m s e l v e s , u t i l i z i n g t o t a l - a b s o r p t i o n y s p e c t r o m e t r y a n d , where r e l e v a n t , d e l a y e d - n e u t r o n - g a m m a c o i n c i d e n c e t e c h n i q u e s , p r o m i s e s t o p r o v i d e a means o f producing the necessary i n f o r m a t i o n i n a reasonable t i m e . Acknowledgments T h i s work was c a r r i e d o u t under t h e a u s p i c e s o f t h e U.S. Department o f Energy under DOE C o n t r a c t No. DE-AC07-76ID01570. 8 7



14. REICH

Nuclear Decay Data

99

[BOE84].

References See, for example, F. Boehm and P. Vogel, Ann. Rev. Nucl. Part. Sci. 34, 125 (1984).

[KLA83].

H. V. Klapdor, Prog. Part. Nucl. Phys. 10, 131 (1983) and references contained therein.

[KRA85].

K.-L. Kratz, private communication (1985); see also Nucl. Phys. A417, 447(1984).

[KRU84].

J. Krumlinde and P. Möller, Nucl. Phys. A417, 419 (1984).

[MAN82].

F. M. Mann, C. Dunn and R. E. Schenter, Phys. Rev. C 25, 524 (1982).

[MAT84].

See, for example, G. J. Mathews, in Proceedings of the NEANDC Specialists Meeting on Yields and Decay Data of Fission Product Nuclides, Brookhaven National Laboratory, October 24-27, 1983, U.S. DOE Report BNL-51778 (1984), pp. 485-502.

[MEA83].

J. W. Meadows, Nucl. Sci. Engr. 85, 271 (1983).

[NDS77].

Nuclear Data Sheets 21, 91 (1977).

[NDS79].

Nuclear Data Sheets 27, 389 (1979).

[RAM83].

S. Raman, B. Fogelberg, J. A. Harvey, R. L. Macklin, P. H. Stelson, A. Schröder and K.-L. Kratz, Phys. Rev. C 28, 602 (1983). [REI85a]. C. W. Reich, in Proceedings of the IAEA Advisory Group Meeting on Nuclear Standard Reference Data, Geel, Belgium, 12-16 November, 1984, IAEA-TECDOC-335 (IAEA, Vienna, 1985) pp. 390-396. [REI85b]. C. W. Reich, "Nuclear Decay Data: Some Applications and Needs", invited paper included in the Proceedings of the International Conference on Nuclear Data for Basic and Applied Science, Santa Fe, NM, 13-17 May, 1985 (to be published). [SMI83].

J. R. Smith, U.S. DOE Report EGG-PBS-6406 (September, 1983).

[TAK72].

K. Takahashi, Progr. Theor. Phys. 47, 1500 (1972) and references contained therein.

[TND76].

Proceedings of the IAEA Advisory Group Meeting on Transactinium Isotope Nuclear Data, Karlsruhe, F.R.G., Nov. 3-7, 1985, IAEA Report IAEA-186, Vols. I-III, (IAEA, Vienna, 1976.)

[TOI78].

Table of Isotopes, 7th Edition, C. M. Lederer and V. S. Shirley, eds., (John Wiley, New York, 1978).

[VAN83].

R. Vaninbroukx and A. Lorenz, in Nuclear Data Standards for Nuclear Measurements, IAEA Technical Reports Series, No. 227 (IAEA, Vienna, 1983) pp. 69-70.

RECEIVED August 11, 1986


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