Neutron fluence monitoring system in mono-energetic neutron fields at FRS/JAEA

Tanimura, Yoshihiko   ; Fujii, Katsutoshi ; Tsutsumi, Masahiro; Yoshizawa, Michio  

Mono-energetic neutron calibration fields have been developed at Facility of Radiation Standards (FRS) using a 4 MV Pelletron accelerator. The neutron energies are available between 8 keV and 19 MeV for determining the energy responses of neutron dosemeters. The neutron energies are well adjusted to the energy points specified in the international standard (ISO 8529-1) and Japanese standard (JIS Z4521). Precise neutron fluence is the most important parameter for the calibration. In order to determine the fluence a Long Counter (hereinafter LC) is installed in the field for monitoring the neutron emission rate from the target. The fluence can be precisely determined using the output counts of the LC, the distance from the target, calibration coefficient of the LC and the air attenuation factor. This presentation describes the neutron monitors, outline of our monitoring system, determination of the air attenuation factor and procedure to determine the neutron fluence.