Progress towards the production of the ^236gNp standard sources and competing fission fragment production

The isobaric distribution of fission residues produced following the bombardment of a natural uranium target with a beam of 25 MeV protons has been evaluated. Decay analysis of thirteen isobarically distinct fission residues were carried out using high-resolution γ-spectrometry at the UK National Physical Laboratory. Stoichiometric abundances were calculated via the determination of absolute activity concentrations associated with the longest-lived members of each isobaric chain. This technique was validated by computational modelling of likely sequential decay processes through an isobaric decay chain. The results were largely in agreement with previously published values for neutron bombardments on ²³⁸U at energies of 14 MeV. Higher yields of products with mass numbers A~110–130 were found, consistent with the increasing yield of these radionuclides as the bombarding energy is increased. - Highlights: • The isobaric distribution of fission residues. • Decay analysis of thirteen isobarically distinct fission residues. • Stoichiometric abundances were calculated via the determination of absolute activity concentrations. • This technique was validated by computational modelling of likely sequential decay processes. • The results were largely in agreement with previously published values for neutron bombardments on ²³⁸U at energies of 14 MeV.