Beta decay measurements are an essential tool to get information in nuclear structure. Besides, beta decay properties are relevant for reactor physics, for instance to estimate the decay heat released immediately after the reactor shutdown which is essentially produced by beta decay of fission products and subsequent gamma ray emission. Antineutrinos emitted by reactors arise from fission product beta decay as well. They are used for elementary particle physics studies and also for applied physics purposes such as non-proliferation. Current studies show that some nuclei interesting for their contribution in reactor antineutrino flux or decay heat calculation might be affected by the so-called Pandemonium effect [1]. This means that current databases are missing some level transition γ energies, which generate a distortion in the estimation of β intensity distribution. These data must be improved and constrained by improved experimental setup and results.
Since this Pandemonium effect is generally linked to the usage of high resolution but low efficiency germanium (Ge) detectors, an alternative detection technique has been developed, based on gamma ray calorimetry with a TAS (Total Absorption Spectrometer) sensitive to the beta population rather than to the individual gamma rays, Such a device can be constructed using large scintillator crystal or an array of scintillator crystals covering a nearly-4π solid angle around the source in order to absorb all emitted gamma rays. In 2009, our group participated to a TAS experiment dedicated to the measurement of beta decay properties of nuclei important for their
contribution in reactor decay heat and reactor antineutrino flux. These measures were performed in collaboration with a team of Spanish researchers from IFIC Valencia at the JYFL accelerator in Finland where the nuclei are produced and precisely selected via a Penning trap [2]. Our team is responsible for the data analysis of 93,92Rb nuclei.
My work consists in the analysis of the experimental data and the investigation of the beta strength distribution for these two nuclei. The obtained beta strength will allow to constrain theoretical microscopic models and will provide important information that are needed inputs in nuclear structure, reactor antineutrino spectrum reconstruction and reactor safety. At this meeting, preliminary results of this analysis will be presented.

1. J. C. Hardy et al., Phys. Lett. 71B, (1977) 307
2. V.S.Kolhinen et al., NIM A 528,776 (2004)