Recent developments in radionuclide neutron source emission rate measurements at the National Physical Laboratory

This paper outlines the key features of the new manganese bath facility of the National Physical Laboratory and describes the measurements performed to characterise and validate the facility. Other developments have focused on the use of MCNP to calculate the fraction of neutrons captured by nuclei other than manganese and the fraction escaping from the bath. This has highlighted the large difference in the oxygen(n,α) capture fraction when different cross-section evaluations are applied. This can change the value obtained for the neutron emission rate of a source by up to 0.8%.