New high dispersion, high resolution X ray spectromete

Kalata, K.

Schnopper, H. W.

English

NASA Technical Reports Server

Measurements of t h e  C r  
. .  
ins t rument  w a s  developed p r imar i ly  f o r  space science ap- 
p l i c a t i o n s  it has  a broad range of a p p l i c a t i o n  f o r  normal 
--..  
. 1aborato;y r e s e a r c h  problems. A s  an example of i t s  per- 
spectrum are presented .  
1 8 2  
formance, measurements of t h e  CrKa 
%The observed, uncorrected fu l l -wid ths  a t  half-maximum 
. .  
i - n t e n s i t y  are: Karl=2. 09eV and Kcr2=2. 67eV. ' Fine  s t r u c t u r e  
. 
, d e t a i l s ,  h i t h e r t o  r epor t ed ,  w e r e  a lso observed. 
. *  
. Work supported i n  p a r t  by t h e  N a t i o n a l  Aeronautics an 
- 
https://ntrs.nasa.gov/search.jsp?R=19690026969 2020-03-23T20:41:46+00:00Z
- 2- 
k Models which account f o r  t h e  product ion of x-rays 
a .  
observed f r o m  celestial  sources  also p r e d i c t  t h e  e x i s t e n c e  
' of d i s c r e t e  s p e c t r a l  f e a t u r e s  i n  t h e  f o r m  of emission l i n e s  
and abso rp t ion  and re-combination edges. These f e a t u r e s  
ins t ruments  of l o w  
have alre'ady 'been observed i n  t h e  . .  solar x-ray spectrum wi th  
t o  modest r e s o l u t i o n  . 2 
' .  An ins t rument  
, x'ray a s t r o p h y s i c s  . -  
e a s i l y  adapted t o  t h e  r e q h r e m e n t s  .of 
which permi ts  g r e a t l y  inc reased  r e s o l u t i o n  
- .  
and d i s p e r s i o n  wi thout  much loss of e f f i c i e n c y  is  shown i n  
Fig.  Ea. ' A  convent iona l  Johann spectrometer3 i s  used wi th  
s e v e r a l  modi f ica t ions .  
large cone angle ,  about loo, is  used t o  i l l u m i n a t e  t h e  c r y s t a l .  
Each r ay  r of t h e  beam is  def ined  by a - h o r i z o n t a l  divergence 
A p o i n t  source  of x r ays  wi th  a 
. .  
-* . 
> 
-t 
CL and a ver t ica l  divergence 9. ' I n  gene ra l ,  t h e  r ay  r ( a , $ )  
s t r i k e s  t h e  c r y s t a l  a t  a Bragg angle  which i s  s l i g h t l y  d i f -  
f e r e n t  fromythat of t h e  c e n t r a l  r ay  (0,O) . The d e v i a t i o n  
f r o m  t h e  c e n t r a l  Bragg ang le  i s  given by 
L --- 
- sin(e,+A) = s in(eB+6)cos$  
-- 
. where cos (e,+6) = C O S ~ ~ C O S ~ .  
. .  
For t h e  s u f f i c i e n t l y  s m a l l  01 and 4 ,  A i s  given 
On t h e  focuss ing  circle,  t h e  polychromatic r e f l e c t i o n  
. .  
p a t t e r n  i s  .concentrated i n t o  a narrow l i n e  which i s  conju- 
g a t e - t o ,  t h e  sou rce  p o i n t .  A t  t h e  focus,  t h e  one-to-one 
' 
correspondence between a p o i n t  i n  t h e  image and a p o i n t  on 
e c r y s t a l  is des t royed  by t h e  astigmatic effects of t h e  
y l i n d r i c a l  l e n s .  It  may, t h e r e f o r e ,  be  p o s s i b l e  fo r  s e v e r a l  
_ .  
wavelengths t o  c o n t r i b u t e  t o  t h e  image a t  one po in t .  A l s o ,  
i g h  r e s o l u t i o n  s t u d i c s  are made d i f f i c u l t  by t h e  l o w  d i s -  
p e r s i o n  a t  t h e  focus.  i s  loss of s p e c t r a l  r e s o l u t i o n  can 
e avoided only  by l i m i t i n g  t h e  v e r t i c a l  and h o r i z o n t a l  
divergence of t h e  beam t o  a s m a l l  range of  angles  about t h e  
. .  
a1 ray  ( t y p i c a l l y  +1/4O). 
The basic improvements i n h e r e n t  i n  our  w concept r e s u l t  
p l a c i n g  t h e  f i l m  or d e t e c t o r  near  t h e  c r y s t a l .  F igure  l b  
. .  
shows t h e  images recorded on x-ray f i l m  placed a t  d i f f e r e n t  
dis tances .  ;long and perpendicular  t o  t h e  l i n e  of t h e  reflected 
c e n t r a l  ray.  The ins t rument  w a s  set  f o r  CrKal. A mica 
c r y s t a l  (R=13.5") which r e f l e c t e d  C r K a  r a d i a t i o n  i n  Sa o r d e r  . . -  'c\ 
w a s  used. A s  t h e  d i s t a n c e  from t h e  c r y s t a l  i n c r e a s e s  (1 
through 7), both t h e  d i s p e r s i o n  and r e s o l u t i o n  are decreased. 
-.c. 
-/ 
A t '  t h e  focus ,  Fig; lb-5, where measurements with t h i s  type  
are usua l ly  made, t h e  d i s t i n c t i o n  between ctl and a2 i s  almost 
t o t a i l y  10s t. 
A high despers ion  photographic image of t h e  CrKala2 
t h  doub le t  i n  8 order (mica) i s  shown i n  Fig.  IC. I n  t h i s  
case t h e  ins t rument  w a s  set wi th  t h e  c e n t r a l  r ay  a t  an ang le  
. .  
-4- 
s l i g h t l y  larger t h a n  eB f o r  Kaz. The f i l m  was rep laced  by 
a p r o p o r t i o n a l  counter  w i th  a p inhole  ape ra tu re  i n  f r o n t  
of t h e  acceptance window. Seve ra l  scans were made i n  t h e  
~ vertical  d i r e c t i o n .  The data were reduce t o  an ene r  
pectrum, Fig.  2 ,  .. through t h e  use of Eqn. 3 .  Seyera l  sca 
. .  
were also made keeping t h e  d e t e c t o r  i n  a f i x e d  p o s i t i o n  
h e ' c r y s t a l  and slowly r o t a t i n g  t h e  c r y s t a l .  With 
u l t i e s  i n h e r e n t  i n  t h e  focussed image removed, 
.. 
he r e s o l u t i o n  i s  l i m i t e d  only by t h e  r e f l e c t i n g  p r o p e r t i e s  
f t h e  c r y s t a l ,  t h e  source  i n t e n s i t y  d i s t r i b u t i o n  and t h e  
s i z e  of t h e  detector ape ra tu re .  
h i t h e r t o  unresolved even wi th  the. best techniques of two 
Seve ra l  s p e c t r a l  f e a t u r e s ,  
. -  
I I ', were observed. c r y s t a l  spectroscopy A- r e c e n t  th ree-  
- 
. *  A ,  ' a .  
. c r y s t a l  spectrometer  s tudy  of  ' t h e  Kal l i n e  by Shah and 
. . .  
DasGupta7 a l s o  shows s i m i l a r  f e a t u r e s .  The ' r e s u l t s  presented  . 
-in Table I a r e  of a p re l imina ry  n a t u r e  and are meant t o  
.) 
.convey t h e  power of t h e  technique. More p r e c i s e ,  h igher  
r e s o l u t i o n  s p e c t r a  and t h e i r  i n t e r p r e t a t i o n  w i l l  be obta ined  
s h o r t l y  and p resen ted  elsewhere. The method of a n a l y s i s  i s  
such t h a t  p r e c i s i o n  bending of t h e  c r y s t a l  i s  n o t  r equ i r ed  
. 
5 -  
s i n c e  any i r r e g u l a r i t i e s  i n  t h e  loc i  of equal  A can be 
determined e m p i r i c a l l y  and t h e i r  e f f e c t s  can be incorpora ted  
i n t o  a computerized a n a l y s i s .  
Optimum use  of t h e  spectrometer  w i l l  be p o s s i b l e  when 
_ .  the p r o p o r t i o n a l  counter  i s  rep laced  by a multi-channel 
0 sens  e es and a 
uorescen t  sc reen .  This  dev ice  
of t h e  photographi'c f i l m .  Rapid 
would then  be t h e  analog 
scanning of  t h e  sc reen  
. .  
would determine t h e  coord ina te s  of each photon and a l i n e  
profile can be ob ta ined  by i n t e g r a t i n g  t h e  i n t e n s i t y  a long 
l i n e s  of equa l  A on t h e  s c r e e n . .  
I 
. .  
The spec t rometer  desc r ibed  i s  i d e a l l y  s u i t e d  t o  t h e  
eeds  of a s p a c e c r a f t  borne ob e rva to ry .  Concentrator  
e l secopes*  already.  i n '  use  g i  h igh ly  space-resolved . 
. .~ 
images which are s u i t a b l e  source  p o i n t s  f o r  t h e  spectrometer .  . _  
The . .  Parge acceptance angle  of t h e  ins t ruments  i n s u r e s  
i m u m  e f f i c i e n c y  . 
The. advice  and h e l p  of Prof .  K; DasGupta was of major 
importance i n  t h e  course  of t h i s  r e sea rch .  M r .  P. K r a m e r  
c . -  
s s i s t e d  us  i n  s e t t i n g  up t h e  experiment and M r .  T. Ou 
a ided  us  i n  t h e  r eco rd ing  and a n a l y s i s  of t h e  d a t a .  
-b- 
- l-  
- 149, 79 (1967). 
*R. Giacconi,  W. P. R e i d  
and T. F. Zehnpfennig, - Space Sci. Rev. 2, 3 ( 1 9 6 9 ) .  
.. f e a t u r e s  which w e  obseived are i n d i c a t e d  by arrows. 
' i The x-ray t u b e  was operated a t  20KV and 20ma. 
Point Source of X-rays 
3 



New high-dispersion, high-resolution X-ray spectrometer - Measurements of the chromium K alpha 1 and 2 lines

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