Computed LET distributions in the build-up region of tissue for 14 MeV neutrons.

Experimental radiobiological investigations of fast neutron beams involve irradiation of thin cell layers. The irradiation of cells is done either in free air or with a material such as graphite, TE plastic or bone-equivalent plastic covering the cells. This paper discusses the computed dose distributions in LET at shallow depths between 5 or 10 micrometers and the equilibrium depth, and the influence of the overlying materials on the distributions. The secondaries considered are elastic recoils of H, C, N and O, and 22 alpha particle groups and the corresponding heavy recoils arising from (n, alpha) events in C, N, O, P and Ca. Dose-average LET and curves of detailed dose distributions in LET as a function of depth in tissue are given for various overlying materials.