A detection system for accurate ([formula omitted], n) neutron counting measurements of low-rate ([formula omitted], n) neutron sources

Abstract

The determination of the (α, n) neutron yield of (α, n) neutron sources with low absolute total neutron emission rates is a challenging task given the complexity of the (α, n) neutron production mechanism, experimental limitations involved with measurements of weak neutron sources, and, for sources containing special nuclear material, concurrence of the production of (α, n) and fission neutrons. However, (α, n) neutron sources are prevalent in a variety of nuclear engineering disciplines – such as nuclear fuel cycle engineering, nuclear safeguards and nonproliferation, and nuclear waste management – and as such, characterization of physical (α, n) neutron sources and accurate representation of (α, n) neutron production in neutron transport codes are critical aspects of these disciplines. In this work, a moderated 3He neutron detector array with high fidelity listmode data acquisition capability was developed for measurements of low-rate (α, n) neutron sources to support (α, n) reaction nuclear data validation needs for nonproliferation applications as well as to provide experimental data for benchmarking (α, n) neutron source modeling methodologies in Monte Carlo neutron transport codes. Measurements were performed of a calibrated Eckert & Ziegler AmBe (α, n) neutron source individually and simultaneously with 252Cf sources of different strengths to simulate pure (α, n) and mixed (α, n) + fission source conditions. Total neutron counting and coincidence analysis methods developed for system data analysis were applied to the measured data, and deduced (α, n) neutron yield values agreed to within 1% of the with the vendor-calibrated AmBe source (α, n) neutron yield traceable to international standards for all measurements. Total (α, n) neutron yield uncertainties for source conditions dominated by (α, n) neutron emission did not exceed 3%.