A long and slender position-sensitive helium-3 proportional counter with an anode wire supported by a ladder-shaped solid insulator

A long and slender position-sensitive 3He proportional counter with an outer diameter of 8 mm and an effective length of 1.2 m has been developed to measure neutron flux distributions in a critical assembly. Because it is difficult to make such a long and slender counter of conventional structure where an anode wire is stretched at the center of a cylindrical cathode tube, three prototype electrode systems of which anode wires are supported by insulator plates have been proposed. Among these three electrode systems, the electrode system of which anode wire is stuck on a ladder-shaped insulator has been adopted. The neutron flux distributions in the core of the Kyoto University Critical Assembly (KUCA) have been measured with the counter. Some non-uniformity of the detection efficiency has been observed throughout the counter. This non-uniformity has been corrected by calibrating the position-dependent detection efficiency with a gold wire activation method. A fairly satisfactory distribution, where the relative deviation from the gold wire activation method is 5.0%, has been obtained. Though the non-uniformity of the detection efficiency should be solved for precise measurements, the counter can be used for quick and rough measurements of neutron flux distributions. (author)