Progress in research of reactor neutron spectra

A review is presented on the progress in the research of the reactor neutron spectra as for the following categories: (1) reactor physics related to the reactor core design, (2) irradiation techniques using reactor neutrons, (3) radiation shielding for reactors, (4) time-dependence of the slowing down neutron spectra in a bulk of the reactor materials, and (5) experimental techniques to measure fast neutron spectra. Brief discriptions are also given for the outstanding experiments and calculations, recently performed in Japan. It is pointed out that further improvement of the experimental techniques for the fast neutron spectra are urgently required. (auth.)