The Dependence of RBE on Energy of Fast Neutrons: 2. Biological Evaluation at Discrete Neutron Energies in the Range 0.43 to 1.80 Mev

Abstract

Seven hundred and sixty 4-week-old female mice were exposed to graded doses of whole-body irradiation with (1) 250 kvp X-rays at 66 r/min, and (2) monoenergetic neutrons at 5 separate energies. The latter, obtained by bombarding a tritium target with 2.8 Mev protons, were delivered at 17 r/hr. Spleen and thymus weight loss 4 days after irradiation indicated RBE (relative biological effectiveness) values of 5.1 for spleen and 4.4 for thymus, declining with increasing energy. Plotting of this data with values at other energies in the literature indicated compatibility with a linear relation to LET (linear energy transfer).