Improving Neutron Source Calibrations at the National Institute of Standards and Technology

The US National Institute of Standards and Technology operates a premier calibration laboratory for certifying the neutron emission rate of radioisotopic neutron sources with rigorous quality assurance over a wide range of emission rates. Calibrations are performed using the manganous sulfate bath technique, and are performed with a relative expanded uncertainty of approximately 3.5% (2σ). Recently, an improvement to the calibration procedure has been implemented whereby, in addition to the national standard neutron source, sources are regularly calibrated against one of three (international) standard sources formerly maintained by the Bureau International des Poids et Mesures. This procedure helps ensure that the fidelity of NIST neutron source calibrations is maintained at the highest level.