A computer program for the development of a fast-neutron spectrometer based on electrochemically etched CR-39 detectors with radiators and degraders

Abstract A computer program, written in FORTRAN 77, is presented, which is capable of calculating the energy-selective response (spots/ n ) of electrochemically etched (ECE) CR-39 to fast neutrons over the energy range 0.6–19 MeV. The computations are based on the principle that, in order to produce “sparkable” trails in a CR-39 detector subjected to ECE, the charged-particle tracks resulting from neutron interactions must fall within definite energy and ECE registration limits. The computer model is based on ECE spot-density measurements in CR-39 detectors placed in conjunction with judiciously chosen thicknesses of a polyethylene radiator and a lead degrader. The optimum thicknesses of the radiator and the degrader, for a given neutron energy, are determined from the program, which computes the neutron detection efficiency (ECE spots/ n ) of CR-39 as a function of the three variables involved (energy of neutron; thickness of radiator; thickness of degrader). Our calculations suggest that it may be possible, with an optimized stack, to obtain a highly peaked response with a typical energy resolution of ∼15–40%. The calculations also indicate that the position of the response peak, and the energy resolution, depend principally upon the degrader thickness, though they are also affected, to a lesser extent, by the radiator thickness.