Neutron kerma values above 15 MeV calculated with a nuclear model applicable to light nuclei

Abstract

Accurate neutron dosimetry is currently dependent on the availability of neutron kerma values (ICRU 1980) to convert absorbed dose as measured with a dosemeter into absorbed dose in tissue. Apart from two experimental determinations at approximately 15 MeV for carbon (Goldberg et al. 1978, De Luca et al. 1983), only calculations based on neutron cross-sections are available. The author has developed a model, applicable to low-mass nuclei, in which experimental nuclear structure information is explicitly included. Details of the model which is based on an intranuclear cascade calculation followed by Fermi breakup (INC/FB) are discussed in Brenner et al. (1981) and Subramanian et al. (1983). The calculations do not include the channel for shape-elastic scattering and this has been separately calculated using an optical potential. Kerma values were calculated for carbon, nitrogen and oxygen at 18 energy points between 16 and 80 MeV, and it was noted that they could be fitted to a simple functional form. The differences between this calculation and others are clearly significant, and ultimately result in significant uncertainties in the calculated absorbed dose delivered during high energy neutron radiotherapy. In principle, the choice of which set of calculations to use should be based on the applicability of the nuclear model to the range of nuclear masses, neutron energies under consideration.