Trapped radiation detector on Mariner  IV space probe measurement of outer Van Allen belt - feasibility of detecting trapped radiation at Mar

Frank, L. A.

Hills, K.

Krimigas, S. M.

Van Allen, J. A.

English

NASA Technical Reports Server

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W o  2-41 5 5  
WASHINGTON, D.C. 20546 WO 3-6925 
C?T95-(=5 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
FOR RELEASE: 11 A,M. EST, MONDAY 
Apr i l  19, 1965 
RELEASE NO: 65-117-C -- 
(One i n  a s e r i e s  of six re leases  based on papers presented 
on Mariner IV experiments a t  the 46th convention of  the 
American Geophysical Union, headquartered a t  the National 
Academy of Sciences, 2101 Const i tut ion Ave., N.W,, Washington, 
D.C., Apr i l  19, 1965.) 
I I - ,  N 65-22 63 2 
&LE -/ I .$ TRAPPED RADIATION EXPERIMENT - 
D r .  James A, Van Allen, S t a t e  Universi ty  of 
D r .  Louis A. Frank, State Universi ty  of  Iowa 
Stamatios M. Krimigas, State Universi ty  of Iowa 
Kent H i l l s ,  S t a t e  Universi ty  of Iowa 
The trapped r ad ia t ion  de tec tor  (TRD) reported sharp increases  
i n  the r ad ia t ion  monitored by t h i s  instrument on Jan. 8 and 12 
and Feb. 5, recorded the bes t  measurement ye t  made on the ou te r  
regions of the Van Allen b e l t s ,  and i s  i n  exce l len t  working 
condi t ion t d  f u l f i l l  i t s  primary objec t ive  of de tec t ing  trapped 
radiatgQn, if any, a t  Mars. 
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This experiment cons i s t s  of four  detectors :  t h ree  Geiger 
Mueller tubes and a s o l i d  s t a t e  detector .  
Tubes A and B w i l l  d e t ec t  protons g r e a t e r  than 500 
thousand e l ec t ron  v o l t s  and e lec t rons  greater than 40 thousand 
e l ec t ron  vo l t s .  
Tube C w i l l  d e t ec t  protons greater than 3.1 mi l l ion  
e l ec t ron  v o l t s  and e lec t rons  g rea t e r  than 150 thousand e lec t ron  
4/15/65 
v o l t s .  > - more - 
https://ntrs.nasa.gov/search.jsp?R=19650013031 2020-03-11T17:27:26+00:00Z
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The s o l i d  s t a t e  de t ec to r  w i l l  measure protons i n  two 
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ranges: from 500 thousand e l ec t ron  v o l t s  t o  11 mi l l ion  e lec t ron  
v o l t s  and from 880 thousand e l ec t ron  v o l t s  t o  four  mi l l i on  
e l e c t r o n  vol t s .  It I s  not  s e n s i t i v e  t o  e lec t rons .  
One of the tubes I s  i d e n t i c a l  t o  one flown on Mariner I1 
t o  Venus ix 1962 and provides a basis f o r  comparing data. 
TRD i s  s e n s i t i v e  t o  low energy protons and e l ec t rons  and during 
the  c ru i se  por t ion  of the f l i g h t  t o  Mars i s  recording g a l a c t i c  
cosmic rays and e lec t rons .  
The 
The TRD made exce l l en t  measurements i n  the ou te r  f r inges  
of  the  Earth 's  magnetosphere, t he  best recorded t o  da te .  The 
readings were made a t  a d i s t ance  from Earth as far as 92,000 
miles .  The f i n a l  evidence of the inf luences of Earth was 
de tec ted  a t  a d is tance  of 104,000 miles. 
A t  approximately 12 mi l l i on  miles from Earth, when t h e  
Ear th  was between the spacecraf t  and the Sun, i t  was expected 
t h a t  t h i s  instrument and o the r s  might d e t e c t  the E a r t h ' s  wake 
formed by the  s o l a r  wind streaming past the  Ear th ' s  magnetic 
f i e l d  and leaves a t r a i l  of r a d i a t i o n  and 
plasma and magnetic f i e l d s  behind the  Earth. 
a per iod centered on Jan. 28, and the  spacec ra f t  was 200,000 
miles  above the Sun-Earth l i n e .  The TRD d i d  no t  d e t e c t  the 
wake a t  t h i s  time o r  within a per iod of t h ree  weeks centered 
on this time. This was the f i r s t  measurement by the  western 
world t o  be made as t h i s  d i s t ance  from Earth and i n  t h i s  d i r ec t ion .  
d i s turbed  s o l a r  
T h i s  was i n  
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The c l a s s  two s o l a r  f lare o f  Peb. 5 was observed by the 
TRD. It recorded l eve l s  50 times normal f o r  p a r t i c l e s  i n  the 
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upper range of  the ins tnunent t s  s e n s i t i v i t y .  
i; 
It was noted during t h i s  event that  the higher energy 
p a r t i c l e s  from the Sun had reached their  peak and were decl ining 
i n  numbers before many low energy p a r t i c l e s  reached the  space- 
c r a f t .  
p a r t i c l e s  move more slowly o r  were def lected more by the  
in t e rp l ane ta ry  magnetic f ie ld .  
It I s  conjectured t h a t  t h i s  is because the lower energy 
P r io r  t o  t h i s  event t h e  Instrument had recorded above-normal 
readings on Jan. 8 and the 12. These readings have not  been 
assoc ia ted  with any hown s o l a r  flares but  the study o f  t h i s  
data is  continuing. 
I n  comparison with measurements by the TRD on Mariner I1 
i n  1962, the TRD on Mariner N is recording much less r ad ia t ion  
in i t s  t r a n s i t  through in te rp lane tary  space. This is bel ieved 
t o  be due t o  the q u i e t  period of the Sun i n  l a t e  1%4 and t h i s  
year as compared with 1962. H i g h e r  energy p a r t i c l e s ,  however, 
are  more numerous than i n  1962, as observed by other  instruments 
aboard the  spacecraf t .  
A t  Mars, the instrument I s  expected t o  de t ec t  trapped 
r a d i a t i o n  assoc ia ted  with any dipole magnetic f i e l d  l a r g e r  
than three  per  cent  of the E a r t h ' s .  
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TRAPPED RADIATION DETECTOR INSTRUMENTS 
The purpose of  t h i s  experiment i s  t o  search f o r  
magnetically trapped r a d i a t i o n  i n  the v i c i n i t y  of Mars that,  if 
i t  e x i s t s ,  might be similar t o  the Earth 's  Van Allen be l t s  
of trapped r ad ia t ion .  
The experiment c o n s i s t s  of  four  de tec tors ,  three Geiger- 
Mueller tubes and one s o l i d  s t a t e  de tec tor ,  a s i l i c o n  diode 
covered with t h i n  n i c k e l  f o i l  t o  exclude l i g h t .  
The three GM tubes are shielded s o  that  low energy 
pa r t i c l e s  can  only e n t e r  by passing through a window a t  the  
end of  each tube. 
The experiment i s  located on the  top of the spacecraf t  
bus and weights about 2-1/4 pounds. 
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Trapped radiation experiment

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