CALCULATIONS OF CHARGED-PARTICLE RECOILS, SLOWING-DOWN SPECTRA, LET AND EVENT-SIZE DISTRIBUTIONS FOR FAST-NEUTRONS AND COMPARISONS WITH MEASUREMENTS

A rapid system has been developed for computing charged-particle distributions generated in tissue by any neutron spectra less than 4 MeV. Oxygen and carbon recoils are derived from R-matrix theory, and hydrogen recoils are obtained from cross-section evaluation. Application to two quite different fission-neutron spectra demonstrates the flexibility of this method for providing spectral details of the different type of charged-particle recoils. Comparisons are made between calculations and measurements of event-size distributions for a sphere of tissue 1 mu m in diameter irradiated by these two neutron spectra. LET distributions have been calculated from computed charged-particle recoils and also derived from measurements using the conventional approximation that all charged particles traverse the chamber. The limitations of the approximation for these neutron spectra are discussed.