The calculation of charged particle fluence and LET spectra for the irradiation of biologically significant materials by neutrons.

As a preliminary step to evaluating recent theories concerning the biological effect of ionizing radiation, the charged particle fluence distributions and the dose distribution in linear energy transfer have been computed analytically for targets of biological and dosimetric interest irradiated by neutrons. Specifically, 14.7 MeV neutrons, the 252Cf neutron spectrum and a cyclotron generated neutron spectrum are considered to irradiate water, tissue-equivalent plastic and standard man tissue and results are given for all these cases. From a knowledge of the target composition, and the cross-sections and kinetics of all the possible neutron induced reactions in the elements hydrogen, carbon, nitrogen and oxygen, the secondary particle spectrum is calculated. By combining with stopping power data for the ions in the target, the charged particle fluence spectra and dose distribution in linear energy transfer are derived. Secondary quantities computed are kerma, energy expended as nuclear elastic scattering, specific ionization and mean quality factor. Stopping powers have been derived from published atomic stopping powers by summing according to the Bragg rule. A comparison between tissue-equivalent plastic and standard man tissue had been made for each of the neutron spectra.