[Basic Knowledge of Neutron: Physics].

Neutrons are uncharged particles and exhibit strong ability to penetrate matter. Various charged particles and gamma rays are emitted from nuclear reactions induced by neutrons passing through the matter. It is important to consider contributions of neutrons for estimating such quantities used in radiation protection as absorbed dose, equivalent dose and effective dose. In this article basic knowledge of neutron is briefly summarized concerned with physical properties of neutrons, neutron reactions, neutron sources, fluence to karma conversion coefficient, absorbed dose, equivalent dose, effective dose.