Repeated measurements of the isotope 115mCd by Los Alamos National Laboratory (LANL), Pacific Northwest National Laboratory (PNNL), and Atomic Weapons Establishment (AWE) have revealed a consistent discrepancy between beta and gamma counting. This suggests that a significant disparity exists between the true value of the isotope’s gamma-ray branching ratios and the values reported by the National Nuclear Data Center (NNDC).
Enriched 114Cd was irradiated using thermal neutrons to produce a high-purity 115m/gCd source for counting and analysis using traditional singles gamma-ray spectroscopy, liquid scintillation counting, gas-proportional counting, and analysis using the new Gamma-Alpha-Beta-Gamma (GAB?) and Gamma-Alpha-Beta Radio-Isotope EvaLuator (GABRIEL) coincidence detection systems. Using the D-T fusion generated neutrons, reduces the wait time required to let the short-lived 115Cd ground state decay away by leveraging the 1:1 production ratio of the ground and metastable state of 115Cd from the 115In (n,p) reaction relative to the 10:1 production ratio of the ground and metastable isotopes of Cd115 by thermal neutron capture on 114Cd. However, the much higher flux in from the Washington State University TRIGA reactor is a more rapid method of production of 115m/gCd but requires access to enriched 114Cd.
High purity 115m/gCd samples were analyzed on regular intervals over a period of 140-days. The activity of 115mCd measured by beta and gamma show a clear discrepancy using the current best known gamma-ray decay branching ratios.
Based on these observations and measurements, a set of new branching ratio recommendations have been produced using conventional counting techniques and the advanced GAB? and GABRIEL instruments.
Published: January 30, 2025
Citation
Archambault B.C., N.E. Uhnak, B.D. Pierson, G.M. Spitler, and J.H. Estrada. 2022.Improvements to the 115g/115mCd Nuclear Data Richland, WA: Pacific Northwest National Laboratory.