Neutron and Capture Gamma Spectra in a Tissue-equivalent Slab for Isotropic Irradiation

The authors present calculated spectra of neutron and capture gamma rays in a 30 cm thick infinite tissue-equivalent slab irradiated on one face by monoenergetic neutrons with energy in the range from thermal to 10 MeV and which are distributed isotropically. The ROZ-5 code was used for the calculation. The program is a complex of one-dimensional programs for solution of the transfer equation in a plane geometry. It is shown that for neutron isotropic irradiation with any spectral distribution: (1) the neutron spectrum in the slab is softens as depth increases to the back surface of the slab; (2) the capture gamma spectrum in the slab has identical shape with the sharp distinguished peaks produced by the 2.2 and 4.5 MeV gamma-rays of the 1H(n, gamma)2H and 14N(n, gamma)15N reactions. The distributions of the neutron absorbed dose and the dose equivalent were calculated in the slab using these data on the neutron spectrum in the slab. These results are in good agreement with data published by other authors.