Reactor Decay Heat in Pu239: Solving the γ Discrepancy in the 4-3000-s Cooling Period

The β feeding probability of Tc102,104,105,106,107, Mo105, and Nb101 nuclei, which are important contributors to the decay heat in nuclear reactors, has been measured using the total absorption technique. We have coupled for the first time a total absorption spectrometer to a Penning trap in order to obtain sources of very high isobaric purity. Our results solve a significant part of a long-standing discrepancy in the γ component of the decay heat for Pu239 in the 4-3000 s range.