Position-sensitive neutron detector with 20 × 20 needle counters

A position-sensitive detector for thermal neutrons was fabricated on the basis of the needle counter. The detector consists of 20 × 20 needle counters with a spacing of 5 mm; the sensitive volume of each needle counter is 4 mm in diameter × 10 mm in length and the filling gas is a mixture of 3He and Q gas (4He + 1%isobutane) with a pressure of 0.3–1.0 MPa. In the position-sensitive detector, a resistor mesh was employed for position encoding by the charge division method. It was found that the encoding method brought about a troublesome distortion in the position image spectrum. In this paper, the performance of the position-sensitive detector is described and the present encoding method is discussed proposing another method without the distortion.