Alpha particle nonionizing energy loss (NIEL)

A method previously developed for proton nonionizing energy loss (NIEL) calculations was extended to alpha particles. The alpha particle NIELs for representative device materials are presented from the damage threshold energy to 1GeV/n. The method used the Ziegler, Biersack, Littmark (ZBL) screened potential for Coulomb interactions and the MCNPX "thin target approximation" for nuclear interactions. The alpha NIEL obtained in this study was compared to the proton NIEL from the previous study. It is seen that for silicon, the NIEL for alphas is about 16 times the NIEL for protons at 1.0 MeV/n where the Coulombic interaction dominates. The ratio drops at higher energies because of the nuclear contributions. Furthermore, a simple radiation transport analysis indicates that in a representative space environment, the contribution of alphas to the damage dose can be comparable to the proton contribution, and that shielding has a marked influence on the relative contributions.