Determination of neutron fluence in 1.2 and 2.5 MeV mono-energetic neutron calibration fields at FRS/JAEA

Tanimura, Yoshihiko   ; Tsutsumi, Masahiro; Yoshizawa, Michio  

1.2 and 2.5 MeV Mono-energetic neutron calibration fields have been developed at Facility of Radiation Standards (FRS) by using a 4MV Pelletron accelerator and employing H(p,n)He reaction. For the calibration, neutron fluence should be precisely evaluated. A silicon semiconductor detector with a polyethylene converter (hereinafter CH-SSD) was developed to determine the neutron fluence. The detection efficiency of a common CH-SSD is not large enough to determine the neutron fluence. Then we developed a CH-SSD with high efficiency by using a large silicon semiconductor detector with 3,000 mm sensitive area. This makes it possible to determine the neutron fluence with satisfactory accuracy. The detection efficiency of the CH-SSD was calculated with NRESP-ANT code and PHITS code. The maximum neutron fluence at 1 m from the target were evaluated to be about 1,000 and 2,000 cms in the 1.2 and 2.5 MeV neutron fields, especially.