Polarization prediction in modulated beam of ground state hydrogen atoms crossed by dc electron bea

Fite, W. L.

Kauppila, W. E.

Ott, W. R.

English

NASA Technical Reports Server

SPACE RESEARCH COORDINATION CENTER 
POLARIZATION OF LYMAN ALPHA RADIATION 
EMITTED BY H(2S)ATOMS IN 
WEAK ELECTRIC FIELDS 
BY 
W. L. F I T E ,  W. E. KAUPPILA AND 
W. R. OTT 
DEPARTMENT OF PHYSICS GPO PRICE $ 
SRCC REPORT NO. 70 
UNIVERSITY O F  PITTSBURGH 
PITTSBURGH, PENNSYLVANIA 
21 FEBRUARY 1968 
CFSTI PRICE(S) $ 
Hard copy (HC) 
Microfiche (MF) b s  - 
ff 653 July 65 
https://ntrs.nasa.gov/search.jsp?R=19680008153 2020-03-12T09:10:00+00:00Z
The SpaceResearchCoordinationCenter, established in May, 1963, has the following functions: (1) it ad- 
ministers predoctoral and postdoctoral fellowship in space-related science and engineedng programs; ( 2) it makes 
available, on application and after review, allocations to assist new faculty members in the Division of the 
Natural Sciences and the School of Engineering to initiate research programs or to permit established faculty 
members to do preliminary work on rearch ideas  of a novel character; (3) in the Division of the Natural Sciences 
it makes an annual allocation of funds to the interdisciplinary Laboratory for Atmospheric and Space Sciences; 
(4) in the School of Engineering it makes a similar allocation of funds to the Department of Metallurgical and 
Materials Engineering and to tbe program in Engineering Systems Management of the Department of Industrial 
Engineering; and (5) in concert with the University's Knowledge Availability Systems Center, it seeks to assist 
in the orderly transfer of new space-generated knowledge in industrial application. The Center also issues pe- 
riodic reports of space-oriented research and a comprehensive annual report. 
Thecenteris supported by an Institutional Grant (NsG-416) from the National Aeronautics and Space Ad- 
ministration, strongly supplemented by grants from the A. W. Mellon Educational and Charitable Trust, the 
Maurice FalkMedical Fund, theRichard King Mellon Foundation and the Sarah Mellon Scaife Foundation. Much 
of the work described in SRCC reports is financed by other grants, made to individual faculty members. 
l e v e l .  
angular d i s t r i b u t i o n  of t h e  Lyman alpha r a d i a t i o n  produced when 
t h e  metastable atoms were quenched i n  a weak dc e l e c t r i c  f i e l d .  
While Stebbings e t  a1 had used a p o l a r i z a t i o n  f r a c t i o n  of u n i t y  
i n  reducing t h e i r  data, Lichten argued t h a t  a p o l a r i z a t i o n  f r a c t i o n  
The po in t  i n  quest ion concerned t h e  p o l a r i z a t i o n  and 
I 
1 
I n  'preparet ion f o r  repeat ing and extending t h e  experiments of 
Ref. 2 an experimental check of; t l ie quench r a d i a t i o n  p o l a r i z a t i o n  
tras c a r r i e d  out i n  an t i c ipa t ion '  t h a t  Lichten's z e r o  po la r i za t ion  
p red ic t ion  would be quickly v e r i f i e d .  I n  t h e  experiment a nodulated 
beam of groundstate hydrogen atoms vas crossed by a dc e l ec t ron  beam 
I 
I 
* 
Research supported by t h e  National Science Foundation. 
. 
2 
and metastable  Ii(  2s) atoms were produced by electron-impact , 
exc i t a t ion .  
s tate atom beam and passed between two p a r a l l e l  p l a t e s  providing 
a.weak e l e c t r i c  quench f i e l d .  The Lyman alpha r a d i a t i o n  produced ' 
by t h e  e l e c t r i c  quenching of t h e  metastable  atoms was dc tec ted  
The I f (  2s) atoms proceeded aomstrenm ir i th  t h e  ground- . .  
at goo with r e spec t  t o  the  quench f i e l d  d i r e c t i o n  and i t s  po la r i za t ion  
w a s  examined using a LiF Rrevs te r ' s  angle  r e f l e c t o r  po la r i za t ion  
de tec to r ,  
counter .  
4 
followed by an oxygen-fil tered iodine-vapor-fi l led photon 
The-quenching f i e l d  ranged from 3 t o  15 v/cm. 
Surpr i s ing ly ,  it vas found t h a t  t h e  , p o l a r i z a t i o n  was  not  zero,  
. t h a t  t h e  i n t e n s i t y  (I,) of t h e  compoiient ,with t h e  e l e c t r i c  f i e l d  
vcc to r  p a r a l l e l  t o  t h e  d i r e c t i o n  of t h e  quench f i e l d  w a s  weaker 
than  t h e  i n t e n s i t y  (Ia) of t h e  opposite p o l a r i z a t i o n ,  and t h a t  t h e  
po la r i za t ion  f r a c t i o n ,  P = (I, - Ia)/(I, + Io) w a s  -0.30 2 0.02, 
after cor rec t ions  for  t h e  f i n i t e  aper ture  and mul t ip l e  r e f l e c t i o n s  
of t h e  Brewster 's  angle  po la r i ze r ,  
and for  c o l l i s i o n  quenching i n  the  r e s i d u a l  gas  i n  t h e  vacuum. 
Checks f o r  experimental  e r r o r s  included changing t h e  d i r e c t i o n  of 
4 f o r  r e s i d u a l  He i n  t h e  beam 
t h e  e l e c t r i c  f i e l d  (the' plane of p o l a r i z a t i o n  t racked)  , changing 
t h e  quench f i e l d  s t r e n g t h ' ( t h e  po la r i za t ion  f r a c t i o n  of  t h e  quench 
r a d i a t i o n  remained cons t an t ) ,  usiqg o the r  quench f i e l d  e lec t rodes  
and configurat ions (no change of r e s u l t s ) ,  varying t h e  exc i t i ng  
e l ec t ron  energy from 10.7 t o  200 eV (no change of r e s u l t s )  and 
I 
. .  
. 
using a magnetic quench f i e l d  r a the r  than  an e l e c t r i c , f i e l d .  With 
t h e  magnetic quench f i e l d  t h e  po la r i za t ion  w a s  zero ,  exac t ly  as 
expected on t h e  b a s i s  of Zeeman mixing of t h e  2*S (m = -$i) and 
. 
1/2 J 
t h e  2% (ni = +%) states with r a d i a t i o n  from the  5 state ,  
l / 2  J 1 /2 
'Riere seemed no ques t ion  t h a t  t h e  apparatus  was working c o r r e c t l y  
and t h a t  e l e c t r i c  f i e l d s  operat,ing on t h e  H(2S) atoms do produce 
part ia  l l y  polar  iz ed qu enc h r a d i  a t  i o n , 
The dilemma presented by these r e s u l t s  i s  now understood thanks 
5 t o  U. Fano who pointed o u t  t h a t  Lichten. l i t i s  . i n  e r r o r  i n  assumj.ng 
t h a t  because t h e  2'??3/2 s ta te  i s  a b o u t ' t e n  t imes as far removed i n  
energy from t h e  2S mctastEble s t a t e  as i s  t h e  2 P s t a t e ,  i t s  e f f e c t s  
c) 
2 
1 / 2  
could b e  neglected i n  the  weak-field S ta rk  q ix ing  problem. Although 
t h e  2% admixture i s  only about  lo$ of t h a t  of t h e  . ?  2 PlI2 s t a t e ,  3/ 2 
both  s t a t e s  should be r e t a ined  i n  a time-independent pe r tu rba t ion  
expansion. The d ipole 'mat r ix  elanent f o r  r a d i a t i o n  t o  t h e  ground 
s t a t e  t hen  c o n s i s t s  of two terms, one involving t h e  2Pl/2 s t a t e  and 
t h e  o the r  t h e  P state.  Upon s q u s r i r e  t o  f i n d  t h e  r a d i a t i o n  
i n t e n s i t y ,  a c ross  prod.uct between these  terms r e s u l t s  which would be 
2 
3/2 
2 b 
of t h e  ord.er of 20% of t h a t  f r m  t h e  P s t a t e  a lone.  
1 /2 
We have worked through t h e  d e t a i l s  of t h i s  elementary c a l c u l a t i o n ,  
neglect ing hyperf ine e f f e c t s ,  and f i n d  t h a t  a p o l a r i z a t i o n  of -32.9% 
is  predic ted .  
experimental  va lue  of -30% and the  t h e o r e t i c a l '  va lue  -32.9: hes any 
Whether t h e  s l i g h t  discrepancy *between' t h e  prel iminary 
s i g n i f i c a n c e  i s  not'known at  present .  
This newer va lue  of t h e  p o l a r i z a t i o n  a f f e c t s  t h e  cross sec t ions  
for e x c i t a t i o n  t o  the  2s s t a t e  obtained f r m  t h e  data of Ref .  2 ,  'oy 
increas ing  t h e  values  approximately 105 above those  given i n  Ref. 3 .  
h s e d  on those data,  t h e  m a x i m ~ m  i i i  t h e  c'ross s e c t i o n  a t  app-oxi-xately 
-I_---- - -..- - - * 
IIote: I n t e r f e r e n c e  tel.ias a-isins from c ross  proclucts i n  squares of sums 
i n  cases sinilar t o  t h i s  have been notcd by o the r s .  
G .  B r e i t ,  Rcv. Ked. Piiys. 2, 31 (1933) and Colepove,  Franken, Imris  and 
Sands,  Phys. Rev. L e t t e r s  2, h2.0 (l35?). 
See f o r  exarnp1.e 
I .  
12 ev would be about 0.18 ~ ( a  which is only about 20% l e s s  than 
0 
6 the recent  ca lcu la ted  value of Burke, Taylor and Ormonde using 
c lose  coupling w i t h  cor re la t ion  terms, 
We are deeply indebted t o  Professor U .  Fano f o r  go in t ing iout  
. .  
t h e  co r rec t  t h e o r e t i c a l  argwnents, thereby making unnecessary a 
'ma,jor e f f o r t  t o  prove even more conclvszbely on experimental 
grounds t h a t  t h e  apparatus was functioning properly,  a n d - t o  
Professor E. .Clerjuoy f o r  h i s  i n t e r e s t  i n  
and o ther  experiments involving hydrogen 
REFERENCES: 
and discussion of t h i s  
. .  . .  
atoms. 
1. 
2. 
3. 
4. 
W. Lichten, Phys. Rev. Le t te rs  5, 12,  1961. 
Stebbings,  F i t e ,  Hummer and Brackmann, Phys. Rev. - 119, 1939, 1960. 
Stebbings,  F i t e ,  Hummer and Brackmann, Phys. Rev. _I 1211, 2051, 1961. 
W. R. O t t ,  W. E. Kauppila and W. L. F i t e ,  Phys. Rev. Le t t e r s  2-9, 
1361, 1967. 
5. U. Fano, p r i v a t e  communication. 
6 .  P. G. Burke, A. J. Taylor and S. Ormonde, Proc. Phys. Soc. (Lond) E, 
336, 3.967. 


Polarization of Lyman alpha radiation emitted by H/2S/ atoms in weak electric fields

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server