A large area position sensitive neutron detector

Abstract

Abstract A 54 × 60 cm 2 position sensitive neutron detector with 0.5 × 1.27 cm 2 resolution has been constructed at the University of Missouri Research Reactor for small angle neutron scattering. It consists of an array of 43 linear position sensitive gas-filled proportional counters 0.5 in. in diameter and 24 in. long. The counters have a fill gas of 6 atm 3 He and 4 atm Ar (with 5% CO 2 ) which yields an area averaged neutron efficiency of 84% at a wavelength of 4.75 A. Position sensing is accomplished by the charge division method. Each of the detector elements is serviced by two charge sensitive, low input impedance preamplifiers and its own single circuit board electronics module. This board contains two nuclear pulse shaping amplifiers, a summing amplifier and lower level discriminator, two 8-bit Wilkinson ADCs and the muprocessor interface circuitry which maps the ADCs into successive locations in the memory/address space of a mucomputer. A FIFO encoder circuit is used to provide the mucomputer with the absolute address in memory of the detector elements which register neutron events. The computer then reads the detector ADCs and forms the charge division quotient by a table look-up divide followed by a high speed multiply. The methods of interdetector position sensitivity and efficiency calibration are discussed. In addition, results of the detector resolution, data acquisition speed and system reliability are presented.