[Basic Knowledge of Neutron: Generation of Neutrons Accompanied with the High-Energy Photon Therapy].

Photo neutrons are generated from high-energy medical X-ray linacs via photo-nuclear reactions with the materials of target and collimator as well as therapeutic X-rays. Such photo neutrons sometimes make unwanted influences and are not negligible for the aspects of radiation protection and radiation control. In this article, fundamental principle of such photo-neutron generation is briefly explained. The side effects induced by the photo neutrons are summarized. In addition, some techniques of the detection and measurement of photo neutrons are introduced.