ABSOLUTE CALIBRATION OF NEUTRON SOURCES HAVING A WIDE RANGE OF EMISSION SPECTRA

An extensive program of neutron source calibrations using an improved manganese bath technique has been completed. Sources generating four neutron spectra were compared at different concentrations of manganese. The results of this work provide correction factors for fast neutron absorption; the Argonne values markedly disagree with some widely accepted work but agree with computations based on the latest cross sections for oxygen and sulfur, compounded with certain assumptions regarding source spectra. Neutron source rates obtained are (3.223 ± 0.014) × 106 neutrons/sec referred to January 1, 1962 for the NRC International Standard source N-200-1, and (1.1776 ± 0.0043) × 106 neutrons/sec for the NBS-II source referred to January 1, 1965. About half of the assigned error is statistical imprecision and the remainder is an estimate of systematic error (all with confidence coefficient of 0.68). Although the result obtained for the international standard agrees with the world average well within the assigned error, there still exist some distinguishable systematic discrepancies with other published data.