Calculation and measurement of neutron-produced single-event spectra

Neutron-produced single-event spectra were measured and calculated for spherical tissue equivalent volumes of cellular and subcellular size (6.5 and 1.0 μm effective diameter, respectively). The experimental spectra were obtained by irradiating a 2 in. Rossi counter with monoenergetic fast neutrons of 0.62, 1.02, 2.01, 3.45, 4.44, and 5.85 MeV. For the calculation, a Monte Carlo program was compiled and executed for the same experimental parameters on an IBM 360/65. Good correlation between experimental and calculated spectra was obtained above 5 KeV/μm. There is, however, strong disagreement in the region of smaller event sizes, which is at least partially due to the fact that the gamma-contamination of the neutron beam was not considered in the calculation. The theoretical spectra were calculated using energy-dependent W values. Spectra, which were evaluated with a constant W value, show a greater deviation from the measured spectra.