Angular and energy distributions of secondary electrons from helium. Slow electrons ejected by electron impact

Recommended angular and energy distributions of slow secondary electrons produced from helium by electron impact are presented in a compact table. The table lists coefficients for the Legendre polynomials from which all angular and energy distributions can be generated for scattering angles between 0° and 180°, secondary-electron energies between 0 and 40 eV, and incident-electron energies between 100 and 2000 eV. The distributions represent double-differential cross sections that are consistent with expected asymptotic behavior, angular symmetry, and integrated cross sections. These cross sections should be sufficiently reliable to serve as normalization standards for experiments on secondary-electron distributions.