Electron Slowing-Down Spectrum in Irradiated Silicon

An electron slowing-down flux spectrum has been measured for $\beta$ particles, $\delta$ rays, and secondaries in neutron-activated silicon over the energy range from a few eV to 30 keV. The spectrum is found to be similar to slowing-down spectra generated in metals by $\beta$ particles. Absolute agreement with predictions of the Spencer—Fano theory is found for energies above 10 keV. Experimental fluxes are somewhat larger for lower energies. A companion theoretical calculation has been carried out based on model cross sections for Si. These include the effects of plasmon creation and electron-hole pair production in the valence band and excitation of electrons from the $K$ and $L$ levels. The latter processes were described on the basis of sum-rule-corrected classical cross sections. Monte Carlo calculations of the slowing-down spectrum were made. The present theory, as well as an empirically shell-corrected Spencer—Attix theory, gives spectra which are smaller than experiment by a factor of ∼ 4 in the 10- to 100-eV range.