Induction filtering for proportional counter amplifiers

The interesting range of the neutron spectrum infusion blankets includes all energies up to 14 MeV. A limited region of this spectrum (from 1 keV to 1 MeV) is amenable to recoil-proton proportional counting and these measurements are now made routinely at the FNS facility at JAERI. One aspect of proportional counter measurements is a consequence of the necessity to acquire data at the lower energies in the presence of much more numerous events of higher energy which overload and saturate pulse amplifiers. Saturation, together with high count rates required for good statistical measurement precision, can introduce systematic errors into the determination of proton recoil distributions. Here we treat this overload distortion problem by a filtering technique designed specifically for the unique ionization response of the proportional counter. Amplifiers having optimal filtering will provide measured proton recoil spectra with substantially less distortion than amplifiers optimized for other types of detectors. 7 refs., 12 figs., 2 tabs