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CALIBRATION OF ISOMER SHIFTS IN THE HEAVY RARE EARTH BY CONVERSION
ELECTRON SPECTROSCOPY
G. Kalvius, P. Maier-Komor, K. Schreckenbach
To cite this version:
G. Kalvius, P. Maier-Komor, K. Schreckenbach. CALIBRATION OF ISOMER SHIFTS IN THE
HEAVY RARE EARTH BY CONVERSION ELECTRON SPECTROSCOPY. Journal de Physique
Colloques, 1980, 41 (C1), pp.C1-61-C1-62. �10.1051/jphyscol:1980111�. �jpa-00219591�
JOURNAL DE PHYSIQUE Colloque c1, supplgment au n O 1, Tome 41, janvier 1980, page C1-61
CALIBRATION OF ISOMER SHIFTS IN THE HEAVY RARE EARTH BY CONVERSION ELECTRON SPECTROSCOPY
X
G.M. Kalvius, P. Maier-Komor and K. Schreckenbach
Physik Department, Technische Universitift MUnchen, 08046 Garching, F.R. Germany.
r I n s t i t u t e Laue-Lrmgevin, F38 GrenobZe-Cedex, France
A b s t r a c t :
The r a t i o of 0 t o N 1 c o n v e r s i o n c o e f f i c i e n t s was measured f o r t h e 9 4 . 7 keV t r a n s i t i o n i n 1 6 5 ~ 0 and 8 2 . 5 keV t r a n s i t i o n i n 1 6 6 ~ 0 , b o t h i n t h e m e t a l and t h e t r i v a l e n t o x i d e . A 3%
i n c r e a s e i n 0 - c o n v e r s i o n was f o u n d f o r t h e m e t a l c a u s e d by t h e a d d i t i o n a l c o n t a c t d e n s i - t y of t h e c o n d u c t i o n e l e c t r o n s . Comparison w i t h i s o m e r s h i f t d a t a on t h e 26 keV t r a n s i - t i o n i n 1 6 1 ~ ~ l e a d s t o a v a l u e o f n t r 2 > = ( 7 . 2 * 1 . 5 ) ~ 1 0-3fm2 f o r t h i s Miissbauer r e s o n a n c e . The d e n s i t y o f e l e c t r o n s a t t h e n u c l e a r
s i t e , t h e c o n t a c t d e n s i t y 9 ( 0 ) , i s o f t e n used t o 0 b t a i . n i n f o r m a t i o n on t h e v a l e n c e e l e c t r o n s t r u c t u r e i n c h e m i c a l compounds.
Changes i n y ( 0 ) d u e t o v a r i o u s c h e m i c a l e n v i r o n m e n t s a r e most e a s i l y d e t e r m i n e d v i a t h e Mossbauer i s o m e r s h i f t :
S = c o n s t . 8 t r 2 > . 9 ( 0 )
The f a c t o r A < r 2
> ,
t h e c h a n g e i n mean square n u c l e a r r a d i u s on e x c i t a t i o n i s g e n e r a l l y n o t known. I t i s f i x e d e m p i r i c a l l y by com- p a r i n g v a l u e s o f S f o r s e l e c t e d compounds w i t h t h e o r e t i c a l c a l c u l a t i o n s o f F ( 0 )[I].
M o s t l y o n e u s e s s e l f - c o n s i s t e n t f i e l d c a l - c u l a t i o n s which a r e s t r i c t l y v a l i d o n l y f o r f r e e i o n s . Q u e s t i o n s t h e n a r i s e a s t o t h e a p p l i c a b i l i t y o f s u c h a scheme t o i o n s bound i n s o l i d m a t e r i a l s .
I n d e p e n d e n t methods of o b t a i n i n g v a l u e s o f y ( 0 ) a r e a v a i l a b l e . F o r gamma t r a n s i t i o n s w i t h MI m u l t i p o l a r i t y i t i s e s t a b l i s h e d t h a t t h e s u b - s h e l l c o n v e r s i o n c o e f f i c i e n t s a r e d i r e c t l y p r o p o r t i o n a l t o t h e s u b - s h e l l c o n t a c t d e n s i t i e s e n s ( 0 ) . F o r e x a m p l e , o n e may l o o k a t t h e c h a n g e s i n o u t e r s h e l l con- v e r s i o n f o r s a m p l e s o f d i f f e r e n t c h e m i c a l n a t u r e . Such m e a s u r e m e n t s have been c a r r i e d o u t m a i n l y f o r 5 7 ~ e and
I g 9 s n
w i t h h i g h r e s o l u t i o n e l e c t r o n s p e c t r o m e t e r s 1 2 1 . I n t h e s e c a s e s , t h e low Z and t h e low t r a n s i - t i o n e n e r g y (-20 keV) a r e o f c o n s i d e r a b l e h e l p . Here we r e p o r t t h e f i r s t measurements f o r n u c l e i a s heavy a s t h e r a r e e a r t h and f o r t r a n s i t i o n e n e r g i e s a s h i g h a s 100 keV.The heavy r a r e e a r t h (Eu-Yb) p l a y an impor- t a n t r o l e i n Mossbauer s p e c t r o s c o p y . T h e i r
i s o m e r s h i f t p r o p e r t i e s h a v e been r e v i e w e d e x t e n s i v e l y 131. S i m i l a r l y much e f f o r t has gone i n t o s e l f - c o n s i s t e n t f i e l d c a l c u l a - t i o n s f o r t h o s e e l e m e n t s [4].
The m e a s u r e m e n t s w e r e p e r f o r m e d w i t h t h e
"on l i n e " e l e c t r o n s p e c t r o m e t e r BILL a t t h e h i g h f l u x r e a c t o r i n G r e n o b l e 1 5 1 . T h i s i n s t r u m e n t p o s s e s s e s an e x t r e m e r e - s o l v i n g power i n t h e r a n g e between 50 and 150 keV and a l l o w s a f u l l s e p a r a t i o n o f N and 0 c o n v e r s i o n l i n e s . We d e t e r m i n e d t h e i n t e n s i t i e s o f t h e 0 and N1 l i n e s ( F i g . l ) f o r b o t h , t h e 94.7 keV t r a n s i t i o n i n
1 6 5 ~ o and t h e 8 2 . 5 keV t r a n s i t i o n i n 1 6 6 ~ o f o r an o x i d e and a m e t a l s a m p l e . The a c t i - v i t i e s w e r e p r o d u c e d by s i n g l e and d o u b l e n e u t r o n c a p t u r e on h i g h l y e n r i c h e d 1 6 4 ~ y t a r g e t s of 501.1g/cm~ t h i c k n e s s . O u r r e s u l t s a r e ,summarized i n t a b l e 1 . The e l e c t r o n i c s t r u c t u r e o f a heavy r a r e e a r t h m e t a l can be r e g a r d e d t o c o n s i s t of t h e a d d i t i o n of an s - d c o n d u c t i o n band t o t h e t r i v a l e n t i o n i c c o r e 16'1. The l a t t e r i s n a k e d l y p r e s e n t i n t h e o x i d e . The 3% i n c r e a s e i n 0 - c o n v e r s i o n i n t h e m e t a l t h u s a r i s e s d i r e c t l y from t h e a d d i t i o n a l c o n t a c t den- s i t y p r o d u c e d by t h e c o n d u c t i o n e l e c t r o n s . T h i s a d d i t i o n a l d e n s i t y i s a l s o t h e o r i g i n o f t h e d i f f e r e n c e i n i s o m e r s h i f t between t h e r a r e e a r t h m e t a l and i t s t r i v a l e n t o x i d e .
We make u s e o f t h e p r o p o r t i o n a l i t y
do = c o n s t
35s
( 0 ) and@,,,, = c o n ~ t $ ~ ~ ( 0 ) I n b o t h c a s e sens
a l s o c o n t a i n s a s m a l l c o n t r i b u t i o n from r e l a t i v i s t i c p I l 2 e l e c -Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980111
C1-62 JOURNAL DE PHYSIQUE
t r o n s . We t h e n u s e t h e D i r a c - F o c k v a l u e f o r ? 4 s ( ~ ) w h i c h i s c o m p a r a t i v e l y s a f e s i n c e we d e a l w i t h a n i n n e r s h e l l . T h i s t h e n g i v e s t h e v a l u e s ? 5 s ( 0 ) l i s t e d i n t a b l e 2. No i s o m e r s h i f t d a t a i s a v a i l - a b l e f o r Ho t h u s we h a v e t o r e f e r t o t h e n e i g h b o u r i n g e l e m e n t Dy. I t h a s b e e n p r o v e n , t h a t t h e r e l a t i v e c h a n g e i n i s o - m e r s h i f t ( ~ ( m t ) - S ( O X $ S ( ~ N i s c o n s t a n t f o r a l l h e a v y r a r e e a r t h . T h u s , a f t e r a s i m p l e c o r r e c t i o n o n y(0) f o r t h e c h a n g e i n Z, t h i s p r o c e d u r e i s s a f e . U s i n g i s o m e r s h i f t d a t a o f t h e 2 6 keV t r a n s i t i o n i n 1 6 1 ~ y ( s e e r e f . 3 ) we f i n d a S / a f ( O ) w h i c h d i r e c t l y d e t e r m i n e s t h e v a l u e o f A(r 2 > o f t h i s r e s o n a n c e . T h e n u m b e r l i s t e d i n t a b l e 2 s h o u l d b e c o m p a r e d w i t h t h e v a l u e
2 3 2
a c r > = ( 7 . 4 x 1 O V ) f m o b t a i n e d f r o m D i r a c - F o c k c a l c u l a t i o n s a n d s h i f t m e a s u r e m e n t s ~ l ] on D ~ a n d D~ + ~ i o n s i n a f l u o r i d e m a t r i x . ~ + The g o o d a g r e e m e n t shows t h a t a t l e a s t f o r
6 A.J. FREEMAN i n " M a g n e t i c P r o p e r t i e s o f R a r e E a r t h M e t a l s " , R. ELLIOT, ed.
P l e n u m P r e s s , New Y o r k 1 9 7 2 .
TABLE i: E x p e r i m e n t a l R e s u l t s :
I
0 . 1 7 5 8 ( 8 ) 0 . 1 7 0 4 ( 7 )
mean: 0 . 0 3 0 ( 7 )
TABLE 2: C o m p a r i s o n w i t h I s o m e r s h i f t d a t a :
,
--
- ----I-----. It h e r a r e e a r t h t h e s e l f - c o n s i s t e n t f i e l d . c a l c u l a t i o n s w o r k w e l l f o r i o n i c s o l i d s a n d t h a t c a l c u l a t e d c o n t a c t d e n s i t i e s c a n b e u s e d w i t h some c o n f i d e n c e .
4 A.J. FREEMAN a n d D.E. E L L I S i n "Moss- 1 8 1 . 5 8 2 . 0 82.5
b a u e r I s o m e r S h i f t s " ( s e e R e f . 2 ) ELECTRON ENERGY ( k e V 1 O u r t h a n k s go t o P r o f . T . v . E g i d y f o r h i s
c o n s t a n t i n t e r e s t i n t h e e x p e r i m e n t , t o r COUHTRATE ( 5 - 1 )
5 W. MAMPE, K. SCHRECKENBACH, P. JEUCH,
B.P.K. MAIER, F. BAUMANDL, J. LARYSZ F i g . 1 : O u t e r c o n v e r s i o n e l e c t r o n 1 i n e s a n d T.v. EGIDY, N u c l . I n s t r . M e t h .
154,
( o x i d e t a r g e t ) o f t h e 82.47 keV1 2 7 ( 1 9 7 2 ) gamma r a y o f 1 6 6 ~ o .
Mr. G. B l a n c f o r t e c h n i c a l a s s i s t a n c e a n d t o D r . P. J e u c h who d e s i g n e d t h e c o m p u t e r - i z e d c o n t r o l s y s t e m o f t h e s p e c t r o m e t e r . R e f e r e n c e s :
1 G.M. KALVIUS a n d G.K. SHENOY, A t o m i c D a t a a n d N u c l e a r D a t a T a b l e s
14,
6 4 3( 1 9 7 4 )
2 F. PLEITER a n d H. DEWAARD i n " M o s s - b a u e r I s o m e r S h i f t s n , G.K. SHENOY a n d F.E. WAGNER, e d s . N o r t h H o l l a n d P u b l .
b
N 1: i I
Co. A m s t e r d a m 1 9 7 8
3 E.R. BAUMINGER, G.M. KALVIUS, a n d I. NOWIK i n " M o s s b a u e r I s o m e r S h i f t s "
( s e e R e f . 2 )