Neutron-detection efficiency of hybrid resistive plate chambers as estimated by using the MC50 cyclotron at KIRAMS

We present the neutron-detection efficiencies of a Gd-coated single-gap resistive plate chamber (RFC) and a LiF-coated double-gap RPC. The experiments were performed by using indirect neutrons provided by the MC50 cyclotron at the Korea Institute of Radiological and Medical Science. Both RPCs show a decrease in the efficiency with increasing beam current, especially the Gd-coated RPC at the highest beam current (50 nA) that we received. Such a decrease in the efficiency could be understood in terms of a decrease in the effective electric field in the gas gap under high-particle-rate environment. The operational plateaus start at about 8 kV for the Gd-coated RPC and at about 6.7 kV for the LiF-coated RPC. The neutron-detection efficiencies of the Gd-coated and the LiF-coated RPCs are about 2.5 and 1.8 %, respectively, at the operational high-voltage-plateau region. These results are completely consistent with the previous efficiencies obtained by using an intense ²⁵²Cf source.