Development of portable long counter with two different moderator materials

Tanimura, Yoshihiko   ; Tsutsumi, Masahiro; Yoshizawa, Michio  

A Long Counter (LC) is the most appropriate detector to measure neutron fluence due to flat response over a wide neutron energy range. Therefore, it is usually employed as a neutron fluence monitor. The weight of the LC used at FRS is 50 kg. It is too heavy to transfer it from one room to another room. Then we developed a new portable long counter whose weight is 15 kg. The portable LC consists of a He or BF counter and a cylindrical moderator. It was designed to have an almost flat response from a few eV to a few MeV. While typical LCs have air gaps in the front surface, which allow lower-energy neutrons to penetrate deeper into the moderator, the portable LC has little space to make such air gaps due to the small size. Then we employed a polystyrene (PS) moderator instead of a polyethylene (PE) one as a front part of the moderator. As the hydrogen density of PS is nearly half that of PE, lower-energy neutrons can penetrate the PS moderator deeper than the PE moderator.