The Primary Cosmic-Ray Electron Spectrum Near Solar Minimum

The Astrophysical Journal1967Vol. 148, pp. 399–399

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Abstract

Two balloon flights were made from Fort Churchill, Manitoba, in the summer of 1965 to continue our investigation of the flux and energy spectrum of the primary cosmic-ray electron component. The spectrum was studied for energies from 20 MeV to 5.5 BeV. Above 1.2 BeV, the differential energy spectrum can be represented by a power la of the form dJ/dE = (48 + 15)E-(2 110 3) electrons . For energies below 1 BeV the spectrum becomes flatter (slope <= 1.6). Between 20 and 270 MeV the total flux rather than the differential flux has been measured. Its value is 180 + 30 electrons . A comparison of our results with data at higher energies obtained by other authors indicates that the spectrum is steeper above 10 BeV ( = 2.45). Our data are also compared with the results obtained from the observations of the non-thermal radio emission from high galactic latitudes. The electron energy spectrum obtained in this experiment is, for energies greater than 1 BeV, in agreement with the spectrum of galactic electrons as derived from the radio-noise measurements. Below 1 BeV the measured electron energy spectrum is flatter than would be predicted on the basis of the radio-noise frequency spectrum for frequencies less than 50 Mc/s (corresponding to electrons below 1 BeV). This might be an indication that solar modulation, even near solar minimum, affects the electron spectrum measured at Earth. The measurements were carried out using a counter system A total-absorbtion lead-glass Cerenkov counter was used to obtain the energy of the electrons Low-energy protons were rejected by the use of a gas (erenkov threshold counter. Guard counters served to identify high-energy protons.

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Abstract

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