Needle counter for neutron counting

A radiation counter with a needle anode has been developed for detection of thermal neutrons; the diameter of sensitive area is 5 mm and the filling gas is the mixture of 3He and Q gas (4He + 1%isobutane) with pressures of 0.3-1.0 MPa. An interesting response has been found in the counter operation for thermal neutrons; there is no proportional-counter region, while it normally works in both ionization-chamber and GM-counter regions. The γ-ray background, which is one of difficulties in the neutron detection, can be effectively removed by the lack of proportional-counter region. In this paper, the performance of the needle counter is described in detail.