Recent activities on neutron standardization in Japan

NMIJ provides national standards on neutron fluence as well as neutron emission rate in Japan. The neutron fluence standards are established for thermal neutrons, monoenergetic neutrons at seven energies from 24 keV to 14.8 MeV, radionuclide-source neutrons from 252 Cf and 241 Am-Be. The neutron emission standards are provided for these radionuclide sources. These are basically prepared in accordance with ISO 8529-1. Worldwide consistency of the standards has been supported by participating in key comparisons organized by BIPM. NMIJ issues calibration certificates accepted worldwide within the range specified in our calibration and measurement capabilities listed in the BIPM web page. The development of the 19 MeV neutron field is in progress to complete standardization in 2011. The radionuclide-source neutron fluence standards were extended in 2008 so that calibrations are also available in terms of ambient/personal dose equivalent. The Japan calibration service system has launched to improve the traceability of neutron measurement in Japan. A new thermal neutron calibration field is developing with a guided beam at the research reactor JRR-3M of JAEA. Aiming at the establishment of the 20-100 MeV high-energy neutron standard, comparison studies are currently being conducted between the cyclotron facilities TIARA of JAEA and CYRIC of the Tohoku University. -1 ) in Japan. We report the present status and recent activities of these neutron standards.