Electron Loss Cross Sections for Helium Atoms in the Kinetic Energy Range 100-450 kev

New measurements of the electron loss cross section for helium atoms in the kinetic energy range 100-450 kev are reported. It has been suggested that previous discrepancies between observers have been partially due to the fact that the neutral beams used contained varying amounts of metastable 1s2s³S₁ atoms, depending on the pressure of the gas in which the He⁰ beam was formed by electron capture from He⁺. It is established that the new measurements were made on helium atomic beams whose loss cross sections were independent of the pressure at which they were prepared over a 10-fold variation. The new values show the same trend with kinetic energy and the same relative values in H₂, He, and air as those previously reported in the 100-450 kev range, but their absolute values are lower. The new values agree with those obtained in other laboratories in the range 100-200 kev. The results are shown in the following table, in units of 10^-17 cm² per atom of gas traversed: