Energy Deposition in Tissue and Similar Materials by 14.1-Mev Neutrons

Fast neutrons produced by the prolific H3(d, n)He4 nuclear reaction and having an average energy of 14.1 Mev (1) are becoming increasingly available to workers in radiobiology. The high neutron yield produced by moderate equipment, low 7-ray contamination (2, 3), and well-defined spectrum make these neutrons a source of choice for many studies. When such facilities are set up for physics work, routine measurements of the neutron flux are almost inevitably made. Whether or not 14Mev neutron sources and flux determinations simultaneously become available to the radiobiologist, however, the associated particle method (1) makes the absolute measurement of the flux certainly as easy, if not easier, than the absolute measurement of neutron dose2 rate. Hence, use of the ratio of dose rate to 14.1-Mev neutron flux may directly facilitate neutron dose measurements for many workers. The difficulties, discussed several years ago by Rossi and Failla (5), with this method of determining neutron doses may now be overcome for the monoenergetic 14.1-Mev neutrons for which many inelastic as well as elastic cross sections and the angular distribution of scattered neutrons have since been determined. Furthermore, ionization methods relying on the Bragg-Gray principle for determining neutron dose in tissue usually require the ratio of dose in the chamber wall to that in tissue exposed to the same flux. Hence, the ratio of dose rate to neutron flux for tissue and other hydrogenous materials is of general interest in neutron dosimetry. Taking into account, in so far as information is available, all the elastic and inelastic reactions of 14.1-Mev neutrons with the common elements of tissue, we present here the method of calculation and values of the dose rate of flux ratio for tissue and several other hydrogenous materials. This investigation of the interactions