Improvements in Antineutrino Spectrum by Including Fission Product Corrections and Calculation of Scatter-Based Pulse Height Distributions

Modeling a reactor’s antineutrino flux spectrum is a critical step in studying its detector response. The first objective of this paper is to study the importance of fission product libraries in the construction of the antineutrino spectrum using the summation method and with various other corrections, including excited states in fission products, finite size, weak magnetism, and radiative corrections. We have used the ENDF/B-VIII.0 and JEFF-3.3 nuclear libraries as our base data to model the antineutrino spectrum. We have also included the total absorption gamma spectroscopy (TAGS) data, which is free from the pandemonium effect, when such data are available. Our analysis includes the newest TAGS data sets from Gombas et al. [Phys. Rev. C, Vol. 103, p. 35803 (2021)] with additions made after the Estienne et al. [EPJ Web Conf., Vol. 211, p. 01001 (2019)] reactor antineutrino spectra study involving TAGS data. The excited state correction has the highest impact on the antineutrino energy spectra, increasing the values 29% to 37% on average in the energy range of 0.5 to 2 MeV. This antineutrino spectra correction also shows an increase of 4.71% to 7.13% in the range of 0 to 2 MeV, with improving excited states using the TAGS data from published literature. Next, antineutrino spectra including the excited state correction using the Gross Theory causes reduction by 11.56% to 69.46% for all four fissionable isotopes in the range of 6 to 8 MeV. The finite size correction, radiative correction, and weak magnetism corrections cause no more than a 3.27% difference between the corrected and uncorrected spectra. We studied the impact of various corrections to the antineutrino spectra and quantified the improvements made in the antineutrino spectrum calculation due to these changes. However, we have not included forbidden decays to simplify the calculations.

The second objective of this work is to determine the impact of spectrum improvements on the coherent-elastic-neutrino-nucleus-scatter (CEνNS)-based detector response because this detection mechanism is more sensitive to lower energy antineutrinos, as expected from a nuclear reactor. We calculate pulse height distributions of Ge- and Si-based CEνNS sensors assuming a 20-eV nuclear recoil threshold. Toward this objective, we formulate pulse height distribution probabilities for different incident antineutrino energies in Ge and Si for a 100-kg detector placed 10 m away from the 1-MW TRIGA reactor with a 20-eV nuclear recoil energy threshold. Our results show that the reaction rate with corrected spectra for a CEνNS-based natural Ge detector is 20.6 events/day and a natural Si detector is 7.18 events/day. The biggest impact on the reaction rates between 38% and 41% is observed due to the excited state corrections. To benchmark our results, we show excellent agreement with the previous antineutrino spectrum calculated by Huber [Phys. Rev. C, Vo. 84, p. 24617 (2011)] and Hayes et al. [Phys. Rev. Lett., Vol. 112, p. 202501 (2014)].