Production and shielding of 15 MeV neutrons

Abstract The characteristics of various types of D-T neutron generators are described and the current status of the development of fast neutron therapy machines is reviewed. For clinical applications a minimum average yield of 4 × 10 12 neutrons/sec is required. However, it is concluded that at present no 15 MeV neutron radiotherapy system can produce this output for a reasonable period of time, e.g. 50 hr. Further developments of all systems are urgently required. The properties of tritium targets are discussed with respect to the target life time and the radiation hazards. Experimental data are presented on the neutron yield as a function of the energy of the bombarding deuterons and target age. The tritium contents of the oil of the accelerator vacuum pumps and the tritium contents of the gas released at the exhaust opening of the rotary pump have been measured. It is concluded that only a small fraction of the total amount of tritium originally present in the target is expelled through the forepump exhaust. With regard to the shielding of 15 MeV neutrons, a summary has been given of experimental attenuation data for various materials.