Fast Neutron Spectroscopy by Proton-Recoil Proportional Counting

Small proportional counters containing hydrogen and without collimation have measured reactor neutron spectra with resolution adequate for comparison with existing energy-group methods of calculation over the energy range from 1 keV to 1 MeV. The counters are efficient and operate satisfactorily at low (10⁵/cm² sec) flux levels. Experimental methods currently in use for in-core measurements using proportional counters vary; the one described here makes use of an electronic pulse-shape discrimination to eliminate the background of gamma radiation. The nature of the numerical procedure required to extract neutron spectra from measured energy distributions of recoil protons bears upon the resolution and statistical precision of the result. Examples of measured neutron spectra are given where they illustrate the various points of experimental technique.