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MEASUREMENTS OF L-SUBSHELL
FLUORESCENCE YIELDS FOR LIGHT ELEMENTS
J. Auerhammer, H. Genz, A. Richter
To cite this version:
J. Auerhammer, H. Genz, A. Richter. MEASUREMENTS OF L-SUBSHELL FLUORESCENCE
YIELDS FOR LIGHT ELEMENTS. Journal de Physique Colloques, 1987, 48 (C9), pp.C9-621-C9-
624. �10.1051/jphyscol:19879104�. �jpa-00227211�
JOURNAL DE PHYSIQUE
Colloque C9, suppl6ment au n012, Tome 48, dhcembre 1987
J. AUERHAMMER, H. GENZ and A. RICHTER
Institut fiir Kernphysik, Technische Hochschule Darmstadt, 0-6100 Darmstadt, F.R.G.
A b s t r a c t :
-
The L - s u b s h e l l f l u o r e s c e n c e y i e l d s ,y ~ i ,
h a v e b e e n d e t e r m i - n e d f o r t h e f i r s t t i m e f o r v a r i o u s l i g h t a n d medlum h e a v y e l e m e n t s w i t h 2 8 < Z < 4 7 . T h e m e t h o d a p p l i e d i s b a s e d o n t h e s u b s h e l l i o n i z a t i o n b y r e l a - t i v i s t i c e l e c t r o n i m p a c t w i t h a n e l e c t r o n e n e r g y o f Eo= 5 0 keV a n d t h e d e t e c t i o n o f c h a r a c t e r i s t i c X r a y s by m e a n s o f a h i g h r e s o l u t i o n c r y s t a l s p e c t r o m e t e r c a l i b r a t e d a b s o l u t e l y w i t h r e s p e c t t o i t s t r a n s m i s s i o n a n d r e f l e c t i v i t y . The n u m b e r o f i n i t i a l L v a c a n c i e s a n d i t s s u b s h e l l d i s t r i - b u t i o n a s w e l l a s t h e n o r m a l i z e d X - r a y t r a n s i t i o n p r o b a b i l i t i e s , t h e C o s t e r - K r o n i g y i e l d s a n d t h e K - s h e l l A u g e r t r a n s i t i o n r a t e s a r e t a k e n f r o m t h e o r y . The r e s u l t s o b t a i n e d f o r w ~ y i e l d v a l u e s t h a t a r e i n agree- i m e n t f o r a l l t h r e e s u b s h e l l s w i t h t h e predictions o f a w i d e l y u s e d s e m i - e m p i r i c a l f o r m u l a a n d f o r w ~ 2 a n d w ~ g a l s o w i t h t h e t h e o r e t i c a l c a l c u l a - t i o n . The v a l u e s o f w ~ l , h o w e v e r , e x c e e d t h e t h e o r y s y s t e m a t i c a l l y .1 . I n t r o d u c t i o n
U n t i l now L - s u b s h e l l f l u o r e s c e n c e y i e l d s , u L i , w e r e m e a s u r e d o n l y f o r h e a v y e l e m e n t s w i t h Z h 4 5 a n d f o r l i g h t e l e m e n t s t h e y c o u l d b e d e d u - c e d s o l e l y f r o m t h e s e m i - e m p i r i c a l f o r m u l a b y K r a u s e [ I ] . However, w i t h t h e a d v e n t o f m o d e r n t h e o r e t i c a l a p p r o a c h e s t o c a l c u l a t e t h e r a t e a n d t h e d i s t r i b u t i o n a t w h i c h a t o m i c v a c a n c i e s a r e p r o d u c e d by a beam o f e l e c t r o n s [ 2 ] , i t h a s become p o s s i b l e t o d e t e r m i n e w L i a l s o f o r l i g h t e l e m e n t s . The m e t h o d a p p l i e d h e r e r e s u l t s f r o m a f o r m e r work by R e u s c h e t a 1 . [ 3 ] . I t i s b a s e d o n t h e s u b s h e l l i o n i z a t i o n by r e l a t i v i s t i c e l e c - t r o n i m p a c t a n d t h e s u b s e q u e n t d e t e c t i o n o f c h a r a c t e r i s t i c X r a y s w i t h
( " ~ u p ~ o r t e d by the Deutsche Forschungsgemeinechaft
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19879104
JOURNAL DE PHYSIQUE
a Bragg s p e c t r o m e t e r and i t r e q u i r e s t h e knowledge o f t r a n s m i s s i o n a n d r e f l e c t i v i t y o f t h e c r y s t a l s p e c t r o m e t e r . The method was a p p l i e d t o s e - v e n e l e m e n t s w i t h 28<Z<47 b y bombarding s o l i d and g a s e o u s t a r g e t s w i t h e l e c t r o n s o f Eo= 50 keV.
2 . E x p e r i m e n t a l T e c h n i q u e .
The e x p e r i m e n t a l a r r a n g e m e n t i s d i s p l a y e d i n F i g . 1 . A d e t a i l e d d e s - c r i p t i o n o f i t i s p r e s e n t e d e l s e w h e r e [ 4 ] . From F i g . 1 , h o w e v e r , i t b e - comes a p p a r e n t t h a t e l e c t r o n s from a n e l e c t r o n gun w e r e f o c u s s e d o n t o g a s e o u s o r t h i n s o l i d a n d i n most c a s e s s e l f s u p p o r t i n g t a r g e t s w i t h a t h i c k n e s s o f t y p i c a l l y 250 pg/cm 2
.
The e m i t t e d c h a r a c t e r i s t i c X-ray r a d i a t i o n from t h e t a r g e t was d e t e c t e d p e r p e n d i c u l a r t o t h e beam a x i s e m p l o y i n g a h i g h r e s o l u t i o n f l a t c r y s t a l Bragg s p e c t r o m e t e r e q u i p p e d w i t h t h r e e d i f f e r e n t c r y s t a l s ( L i F , PET a n d T R A P ) . The c a l i b r a t i o n o f t h e s p e c t r o m e t e r a c c o r d i n g t o i t s t r a n s m i s s i o n a n d r e f l e c t i v i t y was a c h i e v e d f o l l o w i n g t h e p r o c e d u r e d e v e l o p e d by Reusch e t a 1 . [ 3 ] .F i g u r e 2 d i s p l a y s a t y p i c a l example o f an L X-ray s p e c t r u m which was o b t a i n e d b y bombarding a t h i n Ge t a r g e t on C b a c k i n g w i t h e l e c t r o n s of Eo= 5 0 keV a p p l y i n g a TRAP c r y s t a l . The two l a r g e s t p e a k s a r e due t o t h e most p r o m i n e n t Lal a n d LB1 t r a n s i t i o n s , t h e s m a l l o n e s t o t h e weak LB3, 4 t r a n s i t i o n s r e s u l t i n g f r o m i n i t i a l v a c a n c i e s i n t h e L g , L 2 and L , s u b s h e l l s , r e s p e c t i v e l y . On t h e h i g h e n e r g y s i d e o f t h e p e a k s s e v e - r a l s t r u c t u r e s were n o t i c e d w h i c h a r e a t t r i b u t e d t o m u l t i p l e v a c a n c i e s i n t h e f i n a l s t a t e p r i o r t o t h e d e c a y o f t h e s t a t e . The s p e c t r a w e r e
F i g . 1
-
E x p e r i m e n t a l s e t - u p . H e r e i n d e n o t e : 1 - c a t h o d e ; 2-4 p o t e n t i a l g r i d s ; 5-
l e n s ; 6 , 7 , 1 6-
vacuum v a l v e s ; 8-
d e f l e c t i n g m a g n e t ; 9-
S o l l e r s l i t s ; 1 0-
X-ray d e t e c - t o r ; 11-
Bragg c r y s t a l ; 1 2 , 1 3-
h o r i z o n t a l and v e r t i c a l s t e e r e r ; 14-
t a r g e t chamber; 15-
F a r a d a y c u p .a n a l y z e d a p p l y i n g a f i t t i n g p r o c e d u r e t h a t h a s s u c c e s s f u l l y b e e n e m p l o y - e d p r e v i o u s l y [ 3 1 .
I '
I I I Ia d d
J J J L X - r a y s p e c t r u m
\ I /
T P A P c r y s t a l Eo = 5 0 k e V
E n e r g y ( k e V )
F i g . 2
-
Germanium L X - r a y s p e c t r u m o b t a i n e d by b o m b a r d i n g a t h i n ( 2 0 5 pg/cm2) 32Ge t a r g e t w i t h e l e c t r o n s o f 5 0 keV u s i n g a f l a t TRAP c r y s t a l . The d o t t e d l i n e s d i s p l a y t h e r e s u l t o f a f i t t o t h e i n d i v i d u a l d i a g r a m ( L a 1 , L a 2 , LB1, LB3 4 ) a n d s a t e l l i t e ( L a , , LBs) l i n e s . The s o l i d l i n e i s t h eshm
o f t h e i n d i v i d u a l l i n e s .3 . R e s u l t s a n d D i s c u s s i o n
The L - s u b s h e l l f l u o r e s c e n c e y i e l d s f o r 2 8 N i , 29Cu, 32Ge, 3 6 K r , 3 8 S r , 4 2 M ~ a n d 47Ag a r e l i s t e d i n T a b l e I . T h e y w e r e d e d u c e d f r o m t h e X - r a y t r a n s i t i o n r a t e s u s i n g t h e n o r m a l i z e d r a d i a t i v e t r a n s i t i o n p r o b a b i l i - t i e s by S c o f i e l d [ 5 ] , t h e C o s t e r - K r o n i g y i e l d s by K r a u s e [ I ] a n d t h e A u g e r p r o b a b i l i t i e s by Rao e t a 1 . [ 6 1 . The e r r o r s q u o t e d a r e o n t h e
a v e r a g e ~ 1 8 % . The m a i n s o u r c e s o f u n c e r t a i n t i e s o r i g i n a t e f r o m i n a c c u - r a c i e s o f t h e t r a n s m i s s i o n o f t h e B r a g g s p e c t r o m e t e r ( + 9 % ) , o f t h e c r y s t a l r e f l e c t i v i t y ( + 8 % ) a n d i n some c a s e s o f t h e X - r a y a b s o r p t i o n i n s i d e t h e d e t e c t o r window. W h i l e t h e i n a c c u r a c y o f t h e t a r g e t t h i c k - n e s s m e a s u r e m e n t w a s e s t i m a t e d t o b e i n g e n e r a l o f + 4 % , we h a v e a s s i g n e d i n a d d i t i o n a n e r r o r o f + 5 % t o e a c h o f t h e t h e o r e t i c a l q u a n - t i t i e s .
A c o m p a r i s o n w i t h o t h e r e x p e r i m e n t a l d a t a i s p o s s i b l e o n l y i n t h e c a s e o f 4 7 A g . I t s h o w s t h a t t h e v a l u e of B u d i c k a n d Derman [ 7 1 f o r W ~ l i s m o r e t h a n t w i c e a s l a r g e a s o u r v a l u e w h i l e f o r w L 2 a n d e s p e - c i a l l y w , , ~ l o w e r v a l u e s a r e q u o t e d b y t h e a u t h o r s .
--
A s i m i l a r b e h a v i - o u r i s o b s e r v e d f r o m a r e c e n t m e a s u r e m e n t o f w L i f o r 45Rh d e d u c e d byC9-624 JOURNAL DE PHYSIQUE
Table I. L-subshell fluorescence yields
z
2 8N i 2 gC u 3 2G e
3 6K r
3 8S r
42M°
4 7 A8
0, 0.
0.
0.
0.
0.
UL1 .0016±0.
.0017+0.
,0027+0.
.0055+0, ,014 ±0.
,016 +0.
.0003 .0003 .0006
.0008 .002 ,003
"L2 0.0075+0.0014 0.014 ±0.003 0.011 +0.002 0.014 ±0.004 0.030 ±0.005 0.037 +0.005 0.055 +0.009
WL3 0.0055±0.0010 0.012 ±0.002 0.012 ±0.003 0.016 ±0.005 0.034 ±0.005 0.040 ±0.006 0.058 +0.010
the same group [8]. The reason for this discrepancy is not obvious but it might be caused from the poor resolution of the former work and the obstacle that a precise measurement of to., the average L-shell fluores- cence yield, is needed for that method.
The values ofoi. as deduced in the present work are in accordance with the widely used semi-empirical formula by Krause [1]. A comparison with theory [4] shows good agreement with the calculations of Chen et al.
[9] at least for u>. _ and w.,. In the case of u. . , however, the experi- mental values do exceed systematically the theoretical predictions. The
reason for this discrepancy is not obvious.
References
[1] Krause, M.O.: J. Phys. Chem. Ref. Data 8_ (1979) 306 [2] Scofield, J.H.: Phys. Rev. AJ_8 (1978) 963
[3] Reusch, S., Genz, H., Low, W., Richter, A.: Z. Phys. D - Atoms, Molecules and Clusters 3^ (1986) 379
[4] Auerhammer, J., Genz, H., Richter, A.: Z. Phys., in press [5] Scofield, J.H.: At. Data Tables J_4 (1974) 121
[6] Rao, P.V., Chen, M.H., Crasemann, B.: Phys. Rev. AS (1972) 997 [7] Budick, B., Derman, S.: Phys. Rev. Lett. 2_9 (1972) 1055
[8] Markevich, D., Budick, B.: J. Phys. B: At. Mol. Phys. J_4 (1981)1553 [9] Chen, M.H., Crasemann, B., Mark, H.: Phys. Rev. A2_4 (1981) 177
