The Specific Primary Ionization of Cosmic Rays in Helium

Abstract

Values for the specific primary ionization of 46 cosmic rays in helium have been determined from cloud-chamber photographs. A magnetic field allowed separation into two groups: 21 electrons with energies near the energy for minimum ionization had a mean ionization of 7.33\ifmmode\pm\else\textpm\fi{}0.12 per cm, and 26 mesotrons with energies greater than the energy for minimum ionization had a mean ionization of 7.23\ifmmode\pm\else\textpm\fi{}0.12 per cm. The expected value for the latter figure, taking into account a logarithmic rise of ionization with energy, is 8.80 ions/cm. The experimental value for the minimum specific primary ionization in helium (corrected for the ionization in the vapor) is 6.5\ifmmode\pm\else\textpm\fi{}0.1 at N.T.P. Three protons were observed in the ${H}_{\ensuremath{\rho}}$ range in which they can easily be identified; in this ${H}_{\ensuremath{\rho}}$ range three particles constituted approximately one percent of the radiation.