Measurement of the Ratio of Cumulative Spectra of Beta Particles from $${}^{{235}}$$U and $${}^{{239}}$$Pu Fission Products for Solving Problems of Reactor-Antineutrino Physics

Abstract

The first cycle of measurements of the ratio of cumulative spectra of beta particles originating from the isotopes $${}^{235}$$ U and $${}^{239}$$ Pu undergoing thermal-neutron-induced fission was performed. It is found that the curve obtained from our present measurement of the $${}^{235}$$ U $$/^{239}$$ Pu ratio of beta-particle spectra lies 5 $${\%}$$ lower than the analogous curve following from the measurement of a group from Institute Laue–Langevin (ILL). The present analysis reveals that this is due to an erroneous 5 $${\%}$$ overestimation of the $${}^{235}$$ U beta-particle spectrum measured by the ILL group. As a consequence, the results obtained for the $${}^{235}$$ U $$\bar{{\nu}}_{e}$$ spectrum at the production instant via a reconstruction from the cumulative spectrum of beta particles from $${}^{235}$$ U also turned out to be overestimated by 5 $${\%}$$ . These data explain the effect of the reactor antineutrino anomaly.