High-precision measurement of a low Q value for allowed β−-decay of 131I related to neutrino mass determination

The ground-state-to-ground-state β−-decay 131I (7/2+) → 131Xe (3/2+) Q value was determined with high precision utilizing the double Penning trap mass spectrometer JYFLTRAP at the IGISOL facility. The Q value of this β−-decay was found to be Q = 972.25(19) keV through a cyclotron frequency ratio measurement with a relative precision of 1.6 × 10−9. This was realized using the phase-imaging ion-cyclotron-resonance technique. The new Q value is more than 3 times more precise and 2.3σ higher (1.45 keV) than the value extracted from the Atomic Mass Evaluation 2020. Our measurement confirms that the β−-decay to the 9/2+ excited state at 971.22(13) keV in 131Xe is energetically allowed with a Q va…

Observation of an ultralow- Q -value electron-capture channel decaying to As75 via a high-precision mass measurement

Observation of an ultralow-Q-value electron-capture channel decaying to 75As via a high-precision mass measurement

A precise determination of the atomic mass of 75As has been performed utilizing the double Penning trap mass spectrometer, JYFLTRAP. The mass excess is measured to be −73035.519(42)keV/c2, which is a factor of 21 more precise and 1.3(9)keV/c2 lower than the adopted value in the newest Atomic Mass Evaluation (AME2020). This value has been used to determine the ground-state–to–ground-state electron-capture decay Q value of 75Se and β− decay Q value of 75Ge, which are derived to be 866.041(81) keV and 1178.561(65) keV, respectively. Using the nuclear energy-level data of 860.00(40) keV, 865.40(50) keV (final states of electron capture), and 1172.00(60) keV (final state of β− decay) for the exc…

Observation of an ultralow- Q -value electron-capture channel decaying to As 75 via a high-precision mass measurement

Analysis of the total β-electron spectrum of 92Rb : Implications for the reactor flux anomalies

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 92Rb to states in 92Sr 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 er…