Reactor anti-neutrino spectra from total absorption spectroscopy of fission products

Fission process of heavy nuclei $^{\mathrm{235}}$U, $^{\mathrm{238}}$U, $^{\mathrm{239}}$Pu and $^{\mathrm{241}}$Pu generates energy in power reactors. A fraction of this energy and the anti-neutrino emission originate from the decay of fission products. Measurements performed with the Modular Total Absorption Spectrometer (MTAS) help to understand the energy release and emitted anti-neutrino properties. MTAS array of about 1 ton total weight constructed from 19 NaI(Tl) modules packed in a close geometry has been commissioned and used for the decay studies of nearly 80 fission products at ORNL and ANL Analysis of MTAS spectra resulted in the modification of beta-gamma decay schemes and following beta-strength distribution. It was found that the average beta and anti-neutrino energy per decay are substantially reduced and the average gamma energy is increased. The status of MTAS data and their impact on the reactor anti-neutrino spectra properties will be presented.