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 $1s2s{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ atoms, depending on the pressure of the gas in which the ${\mathrm{He}}^0$ beam was formed by electron capture from ${\mathrm{He}}^{+}$. 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 ${\mathrm{H}}_2$, 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 ${10}^{-17\mathrm{}}$ ${\mathrm{cm}}^2$ per atom of gas traversed: