Physical modification of thermal neutron-induced biological effects

The biological effects and/or clinical application of various kinds of high-LET (linear energy transfer) radiation, including neutrons, protons, heavy particles, and pions, have been studied. The fast neutrons have been associated with biological and clinical research, but little is known of the biological effects of thermal neutrons, the final form of fast neutrons that lose energy in the materials. It is difficult to acquire massive thermal neutrons unless a nuclear reactor is available. In this chapter the thermal neutrons are considered as those with energies of 0.250 E-7 MeV. In International Commission on Radiation Units and Measurements (1969), the thermal neutrons are defined as the neutrons with energies with an effective cadmium cutoff of less than about 0.5 eV. Factors regarding thermal neutrons studied in radiation biology can be classified into two categories: Physicotechnological factors and biological factors. These factors are mainly discussed with reference to the radiobiological experiments