Mariner space probe ionization chamber and Geiger counter experiments on galactic radiation entering solar syste

Anderson, H. R.

Neher, H. V.

English

NASA Technical Reports Server

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N E  S NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WO 2-41 5 7  WASHINGTON, D.C. 20546 TELS* wo 7-69?', 
FOR RELEASE: 11 AM. EST MONDAY 
RELEASE NO: 65-117-E April 19, 1965 
h 
(One in a series of six releases based on papers presented on 
Mariner IV experiments at the 46th convention of the Ameqican 
Geophysical Union, headquartered at the National Academy of 
Sciences, 2101 Constitution Ave., NW., Washington, D. C., 
April 19, 1965. 23014 I 
IONIZATION EXPERIMENT 
Professor H. Victor Neher, California Institu'ie of Tech- 
nology 
Dr. Hugh R. Anderson, Jet Propulsion Laboratory 
' Measurements made by the ionization experiment on radia- 
tion entering our solar system from galactic sources are higher 
than reported during the Mariner I1 mission to Venus in 1962. 
This experiment has two functions: A Geiger-Mueller tube 
counts individual particles and an ionization chamber rnaasiires 
the effect of these particles on matter (argon gas). 
this information with the count from the Geiger-Mueller tube 
yields the average energy and electrical charge of the particles 
in the energy ranges above 10 million electron volts for pro- 
tons, 3 million electron volts for!electrons and 40 million 
electron volts for alpha particles. 
Combining 
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The particles measured are principally galactic cosmic 
rays. Other particles measured would be solar cosmic rays or 
trapped radiation. 
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https://ntrs.nasa.gov/search.jsp?R=19650013413 2020-03-11T17:27:29+00:00Z
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It is bel ieved that the higher r a d i a t i o n  l e v e l s  detected 
by thisCexperiment are related t o  the f a c t  t ha t  the Sun i s  i n  
a q u i e t  period of i t s  11-year cycle.  I n  an a c t i v e  per iod the 
Sun's magnetic f i e l d  would be c a r r i e d  outward by a s t rong  s o l a r  
wind forming a s t rong  in t e rp l ane ta ry  magnetic f i e l d  and would 
deflect  energe t ic  p a r t i c l e s  away from the s o l a r  system, as 
was the case with Mariner 11. Mariner IV, however, is being 
subjected t o  a heavier  r a i n  of g a l a c t i c  p a r t i c l e s  because the 
in t e rp l ane ta ry  magnetic f ie ld  i s  not  se rv ing  as a sh ie ld  as 
it d i d  f o r  Mariner 11. 
Conversely, t h e  trapped r a d i a t i o n  de tec to r  measuring 
protons from the Sun is  recording less r a d i a t i o n  than  d i d  the 
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same type of experiment on Mariner I1 because of the q u i e t  
Sun period. 
One p a r t  of t h e  i o n i z a t i o n  experiment, the  Geiger'Mueller 
t u b e ,  failed March 3 s h o r t l y  a f te r  a class two s o l a r  f lare  on 
the Sun. I ts  counting ra te  increased during the s o l a r  f l a r e  
per iod and then  fa i led t o  r e t u r n  t o  a normal l e v e l  and f u r t h e r  
data had t o  be discounted. It is poss ib l e  that the s o l a r  f l a r e  
is  r e l a t e d  t o  the f a i l u r e .  - 
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9 .  r .  -3- 
On March 17, the ion  chamber port ion of the  experiment 
a l s o  failed.  
t o  provide any data. 
bel ieved that the f a i l u r e  was i n  t h i s  area. 
A t  that time both parts of the  experiment ceased 
As both had a common power supply it is  
Ear l i e r ,  however, the experiment had reported measurements 
on the s o l a r  f lare of February 5, and on expected high readings 
i n  the EarthIs  magnetosphere before en ter ing  a r e l a t i v e l y  
lower r a d i a t i o n  a rea  i n  in te rp lane tary  space. 
During the s o l a r  flare on February 5, the  Geiger-Mueller 
tube reported an increase i n  r ad ia t ion  80 times above the  normal 
in t e rp l ane ta ry  i n t e n s i t y  and the Ion chamber reported readings 
200 times normal i n  the  t o t a l  amount of r ad ia t ion  a t  the  l e v e l s  
measured by th i s  experiment, The difference i n  the increase 
recorded by each part of the instrument is due t o  the  ion 
chamber being more s e n s i t i v e  t o  the s o l a r  f l a r e  p a r t i c l e s  
than the Geiger 4 u e l l e r  t u b e  . 
A period centered around January 28, was of i n t e r e s t  because 
the spacecraf t  was a t  i n f e r i o r  conjunction with the  Earth, with 
the Earth between the spacecraf t  and the Sun. It was hoped 
that data returned during this  period might provide measurements 
on the Earthrs wake formed by in t e rac t ion  of the s o l a r  wind and 
the Earthre magnetic f ie ld ,  
12 m i l l i o n  miles from Earth and approximately 200,000 miles  above 
The spacecraf t  was approximately 
the Sun-Earth l i n e ,  
experiment nor  vas it detected by o ther  instruments on the spacecraf t ,  
The wake was not  detected by the  ion iza t ion  
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This suggests that the wake does not extend that far from 
Earth or the wake might have been below the spacecsaft. 
IONIZATION CHAMBER EXPERIMENT 
The ionization chamber is a five-inch stainless steel 
sphere with a wall thickness of 1/100th of an inch. 
serves as a shielding that w i l l  only allow radiation above a 
given level to penetrate. 
The metal 
The sphere is filled with argon gas. Particles that pene- 
trate the sphere leave a trail of ions in the gas. The ions 
are detected and an electric pulse is produced that is propor- 
tional to the rate of ionization in the argon gas. This pulse 
is processed and telemetered to Earth. 
The Geiger-Mueller tube is also shielded to allow pene- 
tration by particles in the same range as detected by the chamber. 
The tube consists of an enclosed volume of gas with two electrodes 
at a different electrical potential. 
The tube generates a current pulse each time a charged 
particle passes through the tube. The tube can count particles 
at a maximum rate of 50,000 per second. 
This experiment weighs 2.9 pounds and I s  located on the 
spacecraft's mast. 
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Ionization experiment

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