A new measurement of the intensity of cosmic-ray ionization at sea level

Abstract

Using a new type of ion chamber, featuring a technique that discriminates against residual wall currents, and a thin plexiglas wall, cosmic-ray ionization measurements have been made at ambient pressures ranging approximately from 71 to 77 cm Hg. A least-squares interpolation at sea level yields an ionization density of (2.18±.05) I. (I corresponds to one ion pair per second per cm3 of NTP air.) The variation with pressure is found to be −3.96%/cm Hg, which compares favorably with the published values of the cosmic-ray barometer coefficient.