Balloon flight data on cosmic ray electron- positron ratio from 100 MeV to 3 Be

Hartman, R. C.

Hildebrand, R. H.

Meyer, P.

English

NASA Technical Reports Server

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OBSERVATION OF THE COSMIC RAY ELECTRON-POSITRON RATIO 
FROM 100 MEV to 3 BEV in  1964" 
** 
R. C. Hartman and Peter Meyer 
Enrico Fermi Institute for Nuclear Studies 
and Department of Physics 
University of Chicago 
and 
R. H. Hildebrand 
Argonne National Laboratory and University of Chicago 
Submitted to 
February 1965 
Journal of Geophysical Research 
* This research was supported in part by the National Aeronautics and Space 
Administration (Grant No. NsG-144-61) and by the Atomic Energy Commission. 
** NASA-Trainee. 
https://ntrs.nasa.gov/search.jsp?R=19660017924 2020-03-16T19:12:08+00:00Z
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OBSERVATION OF THE COSMIC RAY ELECTRON-POSITRON RATIO 
FROM 100 MEV to 3 BEV in 1964* 
R. C. Hartman** and Peter Meyer 
Enrico Fermi Institute for Nuclear Studies and 
Department of Physics 
University of Chicago 
and 
R. H. Hildebrand 
Argonne National Laboratory and University of Chicago 
A determination of the charge ratio of the primary cosmic ray electrons 
provides important evidence for the origin of the electron c,Gmponent. In 1963 DeShong, 
Hildebrand and Meyer (DeShong, et al, 1964a) reported the results of an experiment 
designed to measure this ratio in the energy interval from 100 to 1000 MeV. They 
found an excess of negative electrons which led them to conclude that the electron com- 
ponent consists mainly of  directly accelerated particles. Their data gave an upper l im i t  
for the contribution of electrons and positrons which are produced by proton - proion 
collisions in  the galaxy. 
In this note we present further results from an experiment carried out 
at balloon altitude over Ft. Churchill, and using the same basic equipment (DeShong, 
et al, 1964b)modified for better energy resolution. Although the new data are of 
poorer statistical accuracy than those of 1963 they do extend the energy range of the 
-- 
measurement. 
A schematic diagram of the instrument i s  shown in Fig. 1. A counter 
telescope defines a beam of vertically incident particles passing through the gap of 
* This research was supported in part by the NASA (Grant No. NsG-14461) and 
by the Atomic Energy Commission. 
NASA -T ra i nee. 
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a permanent magnet. Four s p a r k  chambers, having thin aluminum plates, are used to 
measure the deflection of the particles in the magnetic field. The fifth chamber, con- 
taining about 5 radiation lengths of high Z material is used to identify electrons by 
production of photon-electron showers. The modifications with respect to the previously 
used instrument are as follows: 
1. A gas Cerenkov counter i s  used in the counter telescope replacing 
the liquid Cerenkov counter of the earlier experiment. This greatly reduces the amount 
of matter through which a particle must pass before entering the spark chambers and 
thereby reduces the amount of correction for energy loss by bremsstrahlung. This gas 
counter responds only to protons with energies above 17 BeV. The contribution of 
protons to the total number of recorded events i s  therefore small and the proton tracks, 
which furnish straight lines in the spark chamber array, are used to test for resolution 
and bias in the rigidity measurement. 
2. An anticoincidence counter i s  placed under the permanent magnet 
to discriminate against showers produced in the steel of the magnet. 
3. The fiducial system i s  improved for added precision in the measurement. 
Data were obtained from a balloon flight launched at Ft. Churchill r 
on July 16, 1964. They cover an interval of only 55 minutes at which time one of 
the cameras failed. The balloon was still rising and the residual atmosphere decreased 
2 2 
from 9.0 g/cm to 4.5 g/cm during the measurement. 
Because of the short t ime of exposure, the results of the 1964 measure- 
ments which are shown in Table 1 are statistically less significant than those obtained 
in 1963. The energy intervals, however, are much better defined. For comparison 
* 
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. i  
we have included the 1963 data in the table. The measured fraction of positrons i s  
. 
an upper l i m i t  for the primary electron component since no correction i s  made for 
atmospheric secondaries, which wi l l  have a positive excess. 
We may draw the following conclusions from our observation: 
1. The negative excess of electrons between 100 MeV and loo0 MeV 
which was first observed in 1963 i s  confirmed; 
2. Within the limit of our statistical accuracy we find that the negative 
excess extends to at least 3 BeV, showing that also at higher energies accelerative 
processes are the dominant source of primary electrons. The extension of the observation 
to 3 BeV i s  important since a substantial solar contribution to the electron flux at the 
high energies i s  unlikely. 
We are indebted to Mr. J. A. DeShong who designed maior parts and 
participated in the earlier phase of the experiment. I t  i s  a pleasure to acknowledge 
the contributions of A. Cook, J. Upton and S. Lucero in designing, maintaining and 
executing the experiment. N. Metropolis and R. Dornberger provided the computer 
program for analysis of the events and MIS. J. Dil l  was responsible for scanning and 
measuring. 
We gratefully acknowledge the support given us by the Skyhook program, 
U. S. Office of Naval Researchand the hospitality of the Royal Canadian Air Force, 
at Fort Churchill, Manitoba, Canada. 
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References 
DeShong, J. A., R. H. Hildebrand and P. Meyer, Ratio of Electrons to Positrons in 
the Primary Cosmic Radiation, Phys. Rev. Letters - 12, 3 (1964a). 
De Shong, J. A., R. E. Daniels, R. H. Hildebrand and P, Meyer, Spark Chamber and 
Magnet System for Photographing Cosmic-Ray Tracks at Balloon 
Altitudes, Rev. Scient. lnst. 35, - 1035 (1964b). 
Figure Captions 
Fig. 1. Schematic view of the magnet, spark chambers and counter telescope. 
-5 - 
Time 
July- 
Aug. 1963 
Aug. 1964 
TABLE 1. THE FRACTION OF POSITRONS FOR 
VARIOUS ENERGY INTERVALS 
Av. Atmosp, Depth Energy I nterva I 
g/cm* MeV 
50 - 100* 
100 - 300* 
300 - 1000* 
40 - 100 
100 - 300 
300 - lo00 
1000 - 3000 
2 
4 g/cm 
2 
6/4 g/cm 
N+ 
N+ + N- 
0.31 +0.12 
0.38 0.07 
0.16 7 0.04 
0.79 + 0.40 
0.43 7 0.21 
0.30 T 0.14 
0.33 7 0.16 - 
* The energy intervals in the 1963 experiment are not very accurate. Energy losses in I , 
I 
the liquid Cerenkov counter used at that time wi l l  lead to an underestimate of the 
average electron energy. 
Gas 
i 
49 
b '  
m 
3 
CM 
J 1 1  t 1  - -  4 Permanent Magnet(5.5 Kg) ~ - - -  
I k 
8 CM L, -I 3 CM Gap 12x 12 CM2 
Scintillation Anti -Counter 
3 x 12 CM2 Hole 
I 
27CM - -=I t- Scintillation Counter 
6 . 5 ~ 2 2  CM2 
90" Stereo Mirrors ( 5 )  
Shower Spark Chamber 
Fig. I 


Observation of the Cosmic Ray Electron- Positron Ratio from 100 Mev to 3 Bev in 1964

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