High-precision gamma-ray spectroscopic study of the main contributor to the reactor antineutrino spectrum: ⁹²Rb

Two intriguing and unresolved puzzles surround recent measurements and calculations of reactor antineutrino spectra: a deficient in the total number of measured antineutrinos and an excess of antineutrinos for energies from 5-7 MeV. While these observations could point to new physics, a full understanding requires a solid basis of the underlying nuclear physics, namely the beta-decay properties of fission fragments used as inputs to calculate the spectrum. At higher energies in the spectrum, one nucleus, ⁹²Rb, contributes more than 20% to the predicted spectrum. ⁹²Rb was last studied in the 1970’s using primitive detector systems, and thus, revisiting its decay properties is timely. Using the CARIBU facility at Argonne National Lab, we performed a new measurement of the beta-decay of ⁹²Rb. Decays of ⁹²Rb were studied with the SATURN array consisting of 5 HPGe Clover detectors and a large plastic scintillator. The results of the analysis will be presented, including a significantly revised decay scheme. The impact on reactor antineutrino calculations will also be discussed.