Measurement of the Energy Spectra of Cosmic Ray Electron Component and Protons at Ground Level

Using a superconducting magnet spectrometer, we have measured the energy spectra of electrons, positrons, and protons at ground level at an atmospheric depth of 945 g/cm². The differential energy spectrum of the electron component has been determined in the momentum interval between 0.1 and 2.0 GeV/c. This spectrum can be described by two power laws, one below 600 MeV with a spectral index of −1.8 ± 0.1 and the other above this energy with an index of −2.9 ± 0.2. The absolute flux values measured here are not in agreement with the earlier results. The fraction of positrons varies from a value of 0.45 at 200 MeV to about 0.5 above 1 GeV, which is consistent with the theoretical expectation. The momentum dependence of the e/µ ratio in the region between 0.25 and 2.0 GeV/c is proportional to p −2.2, and it appears that the soft component of the ionizing radiation might dominate at ground level at kinetic energies below about 70 MeV. The proton energy spectrum has been determined as a power law in kinetic energy between 2.9 and 19.1 GeV with a spectral index of −2.66 ± 0.26. The p/µ ratio obtained from this experiment seems to have a steeper momentum dependence than from previous experiments.