Laboratory Sources Enhanced in 0.5 eV to 200 keV Neutrons for Instrument Evaluation

Abstract

²³⁸PuBe or SbBe neutron sources in D₂O moderators can provide a spectrum of neutrons useful for checking the dose equivalent sensitivity of neutron detectors from 0.5 eV to 200 keV neutrons. In the calculations, unmoderated spectra of ²³⁸PuBe and SbBe are used as point sources in the center of D₂O spheres. The spectral distribution of the escape neutrons is calculated with a Monte Carlo neutron transport code and is tabulated, together with the dose equivalent rate per unit flux density, for each energy group in the code. Results indicate that intermediate-energy neutrons can be made to contribute up to 74% of the dose equivalent rate of the incident flux density.