Present status of calibration fields for neutron measuring instruments in Japan

The present status of calibration fields for neutron measuring instruments in Japan has been summarized according to the classification of International Standard ISO/DIS 8529, which specifies the neutron reference radiations produced by radioactive sources, electrostatic accelerators and nuclear reactors in an energy range from thermal energy up to 20 MeV, for calibration of neutron measuring devices used for radiation protection purposes. The neutron sources of 252Cf and 241Am-Be are often used for the calibration of neutron measuring instruments in several domestic facilities. The electrostatic accelerators providing protons and deuterons up to an energy of 4 MeV can generate monoenergetic neutrons in the energy range from 10 keV to 20 MeV. Only limited facilities can provide the calibration services to determine the sensitivities or response functions for neutron detectors. Unidirectional beams of thermal and filtered neutrons can be provided by several research reactors. The calibration fields based on the units of neutron emission rate and monoenergetic neutron fluence have been established in some limited facilities but the calibration method for neutron dose equivalent instruments has not been established satisfactorily. It is highly desirable to establish a traceability system for the calibration of neutron measuring instruments used for radiation protection purposes. (author)