Neutron cross-sections and kerma values for carbon, nitrogen and oxygen from 20 to 50 MeV

The advent of high energy neutron radiotherapy will require the neutron cross-section data and kerma factors for elements of biomedical importance to be extended up to and possibly above 50 MeV. Nuclear model calculations have been employed to produce a set of neutron cross-sections for C, N and O from 20 to 50 MeV. The strategy employed involves the optical model fitting of experimental total cross-sections to produce elastic and non-elastic cross-sections. The non-elastic cross-section is then used to normalise the individual reaction cross-sections and charged particle spectra produced by the statistical model of level densities. Kerma values are obtained from charged particle and recoil nucleus spectra. A comparison is made with other kerma calculations, based on the intranuclear cascade-evaporation model, which are consistently lower than the results presented in this paper.