Analysis of the total $\beta$-electron spectrum of $^{92}\mathrm{Rb}$: Implications for the reactor flux anomalies - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Phys.Rev.C Année : 2022

Analysis of the total $\beta$-electron spectrum of $^{92}\mathrm{Rb}$: Implications for the reactor flux anomalies

Résumé

We present here a microscopic nuclear-structure calculation of a β-electron spectrum including all the β-decay branches of a high Q-value reactor fission product contributing significantly to the reactor antineutrino energy spectrum. We perform large-scale nuclear shell-model calculations of the total electron spectrum for the β decay of Rb92 to states in Sr92 using a computer cluster. We exploit the β-branching data of a recent total absorption γ-ray spectroscopy (TAGS) measurement to determine the effective values of the weak axial-vector coupling, gA, and the weak axial charge, gA(γ5). By using the TAGS data we avoid the bias stemming from the pandemonium effect which is a systematic error biasing the usual β-decay measurements. We take fully into account all the involved allowed and forbidden β transitions, in particular the first-forbidden nonunique ones which have earlier been shown to be relevant in the context of the reactor-antineutrino flux anomaly and the unexplained spectral shoulder, the “bump,” the former one having been interpreted as one of the strongest evidence for the existence of sterile neutrinos. Here we are able to present quantitative evidence for the relevance of forbidden nonunique β decays in a total β spectrum of a fission product, in this case Rb92, which is one of the major contributors to the total reactor antineutrino spectral shape. We demonstrate that taking the forbidden spectral shapes fully into consideration leads for Rb92 to a 2.6%–4.6% reduction in the expected inverse β-decay rate at the reactor antineutrino telescopes. We also confirm by our calculation of a total β-electron spectrum that the forbidden transitions can contribute to the formation of the spectral bump in the reactor-antineutrino flux profile.

Dates et versions

hal-03824426 , version 1 (21-10-2022)

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Citer

M. Ramalho, J. Suhonen, J. Kostensalo, G.A. Alcalá, A. Algora, et al.. Analysis of the total $\beta$-electron spectrum of $^{92}\mathrm{Rb}$: Implications for the reactor flux anomalies. Phys.Rev.C, 2022, 106 (2), pp.024315. ⟨10.1103/PhysRevC.106.024315⟩. ⟨hal-03824426⟩
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