An Innovative Method to Measure the Gamma-Ray Emission Probabilities in the Decay of ²³⁸Np and ²³³Pa

The absolute emission probabilities of gamma rays from the decay of ²³⁸Np and ²³³Pa have been measured by an innovative method combining pile oscillation and neutron activation techniques. We obtained values of (24.99 ± 0.34)% and (37.79 ± 0.64)% for the 984.5- and 311.9-keV gamma rays from ²³⁸Np and ²³³Pa, respectively, in good agreement with the recommended values proposed by the Decay Data Evaluation Project (DDEP): (25.18 ± 0.13)% and (38.3 ± 0.5)%. The influence of gamma-ray emission probabilities from ²³⁸Np and ²³³Pa on neutron capture cross-section measurements of ²³⁷Np and ²³²Th, respectively, are discussed and tend to confirm the recommended values from the DDEP. A patent has been granted for this method.