Tk
K F K I 3/1969
ANOMALOUS HYPERFINE FIELD AT RECOILED Rh NUCLEI OF LOW ENERGY
IN Fe Rh ALLOY 51.5 48 5
L Varga, I. Demeter, L Keszthelyi, L. Pócs and Z. Szőkefalvi-Nagy
HUNGARIAN ACADEMY OF SCIENCES CENTRAL RESEARCH INSTITUTE FOR PHYSICS
B U D A P E S T
ANOMALOUS HYPERFINE FIELD AT RECOILED Hh NUCLEI OF LOW ENERGY IN F e ^ - ^ R h ^ g ^ ALL0Y
L .V arg a, I . D em eter, L . K e s z t h e l y i , L .P ó cs and Z. S z ő k e f a l v i - Nagy C e n t r a l R e s e a rc h I n s t i t u t e f o r P h y s i c s , B u d a p e s t, H ungary
The r o t a t i o n a n g le s f o r th e 298 keV and 362 keV s t a t e s o f 103^Rh w ere m easu red a f t e r Coulomb e x c i t a t i o n w ith 2 , 5 MeV p r o to n s i n F e ^ 5 -^ 4 8 5 a l l o y , a s - O.OI72 + 0 ,0 0 3 7 and + 0 ,0 2 9 5 + 0 ,0 1 2 1 r e s p e c t i v e l y .
These v a l u e s a r e i n t e r p r e t e d b y c o n s i d e r i n g th e e x i s t e n c e o f a t r a n s i e n t f i e l d a t s u c h low e n e r g i e s , t o o .
L a s t y e a r we r e p o r t e d th e m easu rem en t o f t h e g - f a c t o r s o f some n u c l e i i n e x c i t e d s t a t e b y o b s e r v in g t h e a n g le coT o f i n t e g r a l r o t a t i o n o f th e a n g u l a r d i s t r i b u t i o n o f th e У - r a d i a t i o n from s t a t e s p ro d u c e d by Coulomb e x c i t a t i o n o f n u c l e i i n f e r r o m a g n e tic a l l o y s [ 1 , 2 , 3 ] . R e c e n tly an a tte m p t was made to m easure i n FeRh w i t h 4 8 .5 a t . % o f Eh th e
g - f a c t o r s o f th e 298 keV 3 /2 “ an d 362 keV 5 / 2 “ s t a t e s o f " ^ E h . The
l i f e t i m e s o f th e s e s t a t e s a re Tj= 9*1 p s e c and T2 = 85 p s e c , r e s p e c t i v e l y [ 4 ] . T h is a l l o y i s f e r r o m a g n e tic [5 ] . The s t a t i c h y p e r f i n e f i e l d a t Rh n u c l e i was m easu red a t 1°K a s Hg t = i3 0 + kG [6] b u t i t s s ig n was n o t d e te r m in e d . The h y p e r f i n e f i e l d a t th e Fe n u c l e i v a r i e s v e r y s lo w ly w ith te m p e r a t u r e s b e lo w th e room te m p e r a tu r e [5 ] • The same i s assum ed f o r th e f i e l d a t t h e Rh n u c l e i . The e x t e r n a l f i e l d a p p l i e d to s a t u r a t e th e Fe-R h t a r g e t was ~ 2000 kO e. The l i q u i d n i t r o g e n c o o le d t a r g e t was bom barded w ith 2 ,5 MeV p r o t o n s .
The a n g u l a r d i s t r i b u t i o n c o e f f i c i e n t s e x p r e s s e d i n te r m s o f co s 2 n e g l e c t i n g b^ w ere found to b e
b 2 (298 keV) = - 0 ,2 5 5 ± 0 ,0 1 2
and b 2 (362 keV) = + 0 ,1 0 3 + 0 ,0 1 5
w ith th e p r e c e s s i o n a n g le s
H i t 298 keV si - 0 ,0 1 7 2 + 0 ,0 0 3 7 (ш ? )2 362 keV = + 0 ,0 2 9 5 + 0 ,0 1 2 1
S in c e ^°^R h i s an odd p ro to n n u c l e u s , t h e S ch m id t l i m i t s g iv e p o s i t i v e g - f a c t o r s f o r t h e s e s t a t e s . T h u s, th e o p p o s i t e s ig n s o f th e m e asu re d
(u>T) / and (to7)2 a r e i n c o n t r a d i c t i o n w i t h th e t h e o r e t i c a l l i m i t s w hich a r e v i o l a t e d o n ly e x c e p t i o n a l l y [7 ] .
- 2 -
T h is c o n t r a d i c t i o n , h o w e v er, can b e o v ercom e, i f one c o n s i d e r s th e a p p e a ra n c e o f a v e r y i n t e n s i v e p o s i t i v e t r a n s i e n t m a g n e tic f i e l d o f s h o r t l i f e t i m e
a t th e n u c l e i a s a r e s u l t o f t h e slo w in g down p r o c e s s and s i m i l a r to t h a t o b s e rv e d i n t h e IMPACT e x p e r im e n ts o f G ro d z in s e t a l . [8 ] . Then, th e m easu red v a l u e s o f 00T7 an d u>T2 c an be d e s c r i b e d a s
(w T) i = - ( H t Tt + H st T j ) i i-1,2 (1)
and th e v a lu e o f
H J t
c a n be c a l c u l a t e d fro m t h e e x p r e s s io n(2)
C o n s id e r in g th e m easu red v a l u e s o f ( t o T ) f and ( c o T a s w e ll a s th e S c h m id t l i m i t s ( 0 ,0 4 5 - 7 ,3 ) o f g]_ / g2 , th e r a t i o i n (2) must b e p o s i t i v e . I t f o ll o w s t h a t
1 . The s i g n a d o p te d fro m r e f . [8] f o r b e i n g p o s i t i v e , r e q u i r e s t h a t o f Hg j. t o be n e g a t i v e . T h is i s c o n s i s t e n t w i t h th e m e a su re d p o s i t i v e s i g n o f (coT)2 an<i* i f one a c c e p t s th e S ch m id t p r e d i c t i o n o f g2 , t h i s
p o s i t i v e s i g n i s n o t i n c o n s i s t e n t w ith th e e x i s t e n c e o f ow ing to th e r e l a t i v e l y h ig h v a lu e o f T2 •
2 . W ith in t h e l i m i t s o f th e S c h m id t p r e d i c t i o n o f g-, / g2 th e v a l u e o f Ht Tt i s a lw ay s => 0 and l i e s i n t h e r a n g e o f th e t r a n s i e n t f i e l d v a l u e s o b s e rv e d i n h ig h r e c o i l e n e rg y e x p e r im e n ts on th e n e ig h b o u r in g
e le m e n ts (P d , Rn, C d ): 9*Ю ~^ Gauss s e c [8] ( s e e P i g . l ) .
I f , we a t t r i b u t e t h e 20% d i f f e r e n c e o f t h e m e asu re d (c o l) = 0 ,0 7 7 ± 0 ,0 0 5 o f t h e 528 keV s t a t e o f x^ P t o b ta in e d on Coulomb e x c i t a t i o n w ith 2 ,5 MeV p r o to n s [3 ] fro m th e s t a t i c v a lu e o>T= 0 ,0 9 5 + 0 ,0 0 3 C91 n o t a s i n [3 ] t o c r y s t a l l i n e e f f e c t , b u t t o t h a t o f t h e t r a n s i e n t f i e l d , we g e t f o r H+- ¥+. =
= + ( 1 1 »6 + 4 ,3 ) 1 0 " 0 G auss s e c , i n s u r p r i s i n g l y good a g re e m e n t w ith t h e + ( 1 6 ,2 + 4 , 1 ) . 1 0 " ° G auss s e c . e v a l u a t e d from IMPACT e x p e r im e n ts a t 12 MeV r e c o i l e n e r g i e s o f 1 •' ^Pt.
The e f f e c t o f th e r e c o i l e n e rg y on t h e v a lu e o f cuT f o r th e 847 keV s t a t e i n v ^Fe h a s b e e n a l r e a d y i n v e s t i g a t e d i n two e x p e r im e n ts [ 1 0 ,1 1 ] . 'T h e ir
- 3 -
r e s u l t s a r e c o n t r a d i c t o r y . The p r e s e n t r e s u l t c o n f ir m s th e o b s e r v a t i o n s i n th e l a t t e r e x p e r im e n t [ 1 1 ] .
The e x i s t e n c e o f t h e h ig h i n t e r s i t y t r a n s i e n t f i e l d ev en a t r e c o i l e n e r g ie s o f maximum 100 keV , w hich seem s to b e e v i d e n t fro m th e p r e s e n t e x p e r im e n t, c a n n o t be a t t r i b u t e d to th e e l e c t r o n p r o c e s s e s s u g g e s te d f o r t h e e x p la n a t i o n o f th e t r a n s i e n t f i e l d o b se rv e d i n IMPACT m e a su re m e n ts. The v e l o c i t i e s a t s u c h low r e c o i l e n e r g i e s a r e to o s m a l l f o r p i c k i n g up e l e c t r o n s from Fe, t h e e n erg y l o s s i s m a in ly n u c l e a r [8] s in c e e l e c t r o n p r o c e s s e s , su c h as i o n i z a t i o n , c h a r g e ex ch an g e c e a se t o be i m p o r t a n t . However, t h e s i m i l a r v a lu e s o f th e t r a n s i e n t f i e l d a t th e h i g h and low r e c o i l e n e r g i e s s u g g e s t
a common o r i g i n . T h is i s th o u g h t t o b e t h e f i n a l s t a g e o f th e s lo w in g
down p r o c e s s when th e slow moving r e c o i l e d n u c l e i a p p ro a c h e i n t h e c o l l i s i o n s th e p o l a r i z e d Fe h o s t atom s b y w hich t h e s - e l e c t r o n s o f th e r e c o i l p a r t i c l e become s t r o n g l y p o l a r i z e d , t o o , and p ro d u c e a t r a n s i e n t f i e l d b y c o re
p o l a r i z a t i o n . The o b se rv e d e f f e c t o f H^. f ^ з е е т з to be th e i n t e g r a t e d c o n t r i b u t i o n fro m t h e s e i n v i d u a l c o l l i s i o n s .
To g e t a b e t t e r i n s i g h t i n t o th e s e i n t r i c a t e phenom ena, i t w o u ld be o f i n t e r e s t to c o n tin u e t h e i r s t u d y , p o s s i b l y , by v a r y i n g th e e n e r g y o f th e r e c o i l e d p a r t i c l e s .
R e fе г е п с е з
1 . L . R e s z t h e l y i , I .D e m e te r , Z. S z ő k e f a lv i- N a g y and Z .z á m o r i, i n H y p e rfin e S t r u c t u r e and N u c le a r R a d i a t i o n , e d . b y E . M a tth ia s and D . A .S h i r l e y / N o r t h -Но11and P u b l i s h i n g Company, A m sterdam , 1 9 6 8 /.
p .1 9 2 .
2 . L . R e s z t h e l y i , I . D em eter, Z.SzőkefaJ.vi_Nagy a-Qd L .V a rg a , N u c l.P h y s . A120 (1 9 6 8 ) 5 4 0 .
5 . L . V a rg a, I . D e m e te r, L .K e s z t h e l y i , Z .S z ő k e f a lv i- N a g y and Z .Z á m o ri, P h y s.R e v . / t o b e p u b l i s h e d / .
4 . F.K.McGowan an d P .H .S t e l s o n , P h y s .R e v . 109 (1 9 5 8 ) 9 0 1 .
5 . G .S h ir a n e , C.W. Chen, P .A .F lin n an d R .N a th a n s , P h y s .R e v . 151 (1965) 1 8 5 .
6 . B .D re y fu s , P .S 'te ts e n k o and D .T h o u lo n z e , P h y s. L e t t e r s 24A (1 9 6 7 ) 454.
7 . E. B o d e n s te d t and J .D .R o g e r s , i n P e r t u r b e d A n g u la r C o r r e l a t i o n s , ed . by E .K a r ls s o n , E .M a tth ia s and K .S ie g b a h n /N o r th - H o ila n d P u b li s h i n g Company, A m sterdam , 1 9 6 4 ./ p .9 1 .
8 . L .G r o d z in s , i n H y p e rfin e S t r u c t u r e and N u c le a r R a d i a t i o n , e d .b y .
E . M a tth ia s and D .A .S h ir l e y /N o r th - H o lia n d P u b l i s h i n g Company, Amsterdam, 1 9 6 8 / . p .6 o 7 .
R .R .B o r c h e r s , J .D .B r o n s o n , B .K e r s k in d , L .G r o d z in s , R .K a lis h and D.E.
M u rn ic k , P b y s. Rev. L e t t e r s 20 (1 9 6 8 ) 4 2 4 .
9 . R .B e ra u d , I . B e r k e s , J . D a n ie r e , M .Lévy, G .M a re s t, R .R ougny, H .B ern as and D .S p a n J a a rd , i n H y p e rfin e S t r u c t u r e and N u c le a r R a d i a t i o n , e d .b y . E .M a tth ia s and I ) ,A .S h i r l e y / N o r th - H o lla n d P u b l i s h i n g Company,
A m sterdam , 1 9 6 8 / p.199*
1 0 . R .K a lis h and W .J .K o s s le r , P h y s .R e v .L e t t e r s 20 (1 9 6 8 ) 2 7 1 .
1 1 . D .E .M u rn ic k , I.R .M c D o n a ld , R .R .B o r c h e r s , G .H ee stan d and B .H e r s k in d , C o n fe re n c e on I o n I m p l a n t a t i o n and H y p e rfin e I n t e r a c t i o n s , L ondon, 1 9 6 8 . / u n p u b l i s h e d / .
- 5 -
F i g . 1 V a r i a t i o n o f Ht T t w ith g 1 / g2 .
The a rro w s m ark th e l i m i t s o f t h e S ch m id t p r e d i c t i o n . The e s t i m a t e d e r r o r o f Тд_ and / T 2 i s 10 %.
Ob в
- 6
fig. 1.
P r i n t e d i n th e C e n t r a l R e s e a rc h I n s t i t u t e f o r P h y s i c s , B u d ap e st K ia d ja a K ö n y v tá r- é s K ia d ó i O s z t á l y . O. v . s d r . F a rk a s I s tv á n n á Szakm ai l e k t o r : Zám ori Z o l t á n . N y e lv i l e k t o r : K ovács Jen ő n é P éld án y szám : 100 Munkaszám: KFKI 4170 B u d a p e s t, 1969 J a n u á r 3*
K é s z ü lt a KFKI h á z i s o k s z o r o s í t ó j á b a n . F . v . : Gyenes Im re
