Determination of the 242Pu Branching Ratio via Alpha-Gamma Coincidence

When the burn-up is high, the 242Pu isotopic content becomes more important. The traditional correlation method 1 will fail. The 242Pu isotopic content in the sample plays an essential role if the neutron coincidence method is used to quantify the total amount of plutonium. In one of the earlier measurements 2 we had a chance to measure an isotopic pure (> 99.95 %) 242Pu thick sample and realized that the difference in the branching ratio (BR) value among current nuclear data 3) for the two important gamma-rays at 103.5-keV and 158.8-keV. In this study, the thick sample was counted on a 15% ORTEC safeguards type HPGe to further improve BR determination of the 159-keV gamma-ray. Furthermore, we have made a thin 242Pu sample from the thick sample and performed alpha-gamma coincidence measurements. Our preliminary gamma-ray BR results are 4.37(6) E-4, 2.79(8) E-5, and 2.25(8) E-6 for 44.9-keV, 103.5-keV, and 158.9-keV, respectively.