Cross Sections for Electron Capture by Fast Protons inH2, He,N2, and Ar

Abstract

Cross sections for electron capture by protons have been measured at energies from 440 keV to 13.8 MeV in ${\mathrm{N}}_2$ and in Ar; to 5.41 MeV in He; and to 2.45 MeV in ${\mathrm{H}}_2$. Electron-loss cross sections in the same gases at 1.027 and 2.44 MeV are also presented. The measurements were carried out by analysis of particle-beam composition after exit from a gas target of known composition and thickness. The beam was separated magnetically, and the charged and neutral components were detected by a Faraday cup and a scintillator, respectively. The energy range of our results overlaps that of Barnett and Reynolds between 440 keV and 1 MeV. Our electron-capture cross sections in this region agree within the experimental uncertainty for ${\mathrm{H}}_2$ and He, but are larger by up to 50% in ${\mathrm{N}}_2$ and Ar.