Direct determination of the atomic mass difference of the pairs As 76 − Se 76 and Tb 155 − Gd 155 rules out As 76 and Tb 155 as possible candidates for electron (anti)neutrino mass measurements

Measurement of the $2^+\rightarrow 0^+$ ground-state transition in the $\beta$ decay of $^{20}$F

We report the first detection of the second-forbidden, non-unique, $2^+\rightarrow 0^+$, ground-state transition in the $\beta$ decay of $^{20}$F. A low-energy, mass-separated $^{20}\rm{F}^+$ beam produced at the IGISOL facility in Jyv\"askyl\"a, Finland, was implanted in a thin carbon foil and the $\beta$ spectrum measured using a magnetic transporter and a plastic-scintillator detector. The $\beta$-decay branching ratio inferred from the measurement is $b_{\beta} = [ 0.41\pm 0.08\textrm{(stat)}\pm 0.07\textrm{(sys)}] \times 10^{-5}$ corresponding to $\log ft = 10.89(11)$, making this one of the strongest second-forbidden, non-unique $\beta$ transitions ever measured. The experimental resu…

Direct measurement of the mass difference of $^{72}$As-$^{72}$Ge rules out $^{72}$As as a promising $\beta$-decay candidate to determine the neutrino mass

We report the first direct determination of the ground-state to ground-state electron-capture $Q$-value for the $^{72}$As to $^{72}$Ge decay by measuring their atomic mass difference utilizing the double Penning trap mass spectrometer, JYFLTRAP. The $Q$-value was measured to be 4343.596(75)~keV, which is more than a 50-fold improvement in precision compared to the value in the most recent Atomic Mass Evaluation 2020. Furthermore, the new $Q$-value was found to be 12.4(40)~keV (3.1 $\sigma$) lower. With the significant reduction of the uncertainty of the ground-state to ground-state $Q$-value value combined with the level scheme of $^{72}$Ge from $\gamma$-ray spectroscopy, we confirm that th…

Microscopic calculation of the $\beta^-$ decays of $^{151}$Sm, $^{171}$Tm, and $^{210}$Pb with implications to detection of the cosmic neutrino background

The electron spectral shapes corresponding to the low-$Q$ $\beta^-$-decay transitions $^{151}$Sm$(5/2^-_{\rm g.s.})\to\,^{151}\textrm{Eu}(5/2^+_{\rm g.s.})$, $^{151}$Sm$(5/2^-_{\rm g.s.})\to\,^{151}\textrm{Eu}(7/2^+_{1})$, $^{171}$Tm$(1/2^+_{\rm g.s.})\to\,^{171}\textrm{Yb}(1/2^-_{\rm g.s.})$, $^{171}$Tm$(1/2^+_{\rm g.s.})\to\,^{171}\textrm{Yb}(3/2^-_{1})$, $^{210}\textrm{Pb}(0^+_{\rm g.s.})\to\,^{210}\textrm{Bi}(1^-_{\rm g.s.})$, and $^{210}\textrm{Pb}(0^+_{\rm g.s.})\to\,^{210}\textrm{Bi}(0^-_{1})$ have been computed using beta-decay theory with several refinements for these first-forbidden nonunique (ff-nu) $\beta^-$ transitions. These ff-nu $\beta^-$ transitions have non-trivial electro…

High-precision electron-capture Q value measurement of 111In for electron-neutrino mass determination

A precise determination of the ground state $^{111}$In ($9/2^+$) electron capture to ground state of $^{111}$Cd ($1/2^+$) $Q$ value has been performed utilizing the double Penning trap mass spectrometer, JYFLTRAP. A value of 857.63(17) keV was obtained, which is nearly a factor of 20 more precise than the value extracted from the Atomic Mass Evaluation 2020 (AME2020). The high-precision electron-capture $Q$ value measurement along with the nuclear energy level data of 866.60(6) keV, 864.8(3) keV, 855.6(10) keV, and 853.94(7) keV for $^{111}$Cd was used to determine whether the four states are energetically allowed for a potential ultra-low $Q$-value $\beta^{}$ decay or electron-capture deca…

Estimated solar-neutrino capture rates of 131Xe : implications for multi-tonne Xe-based experiments

Various large-scale experiments for double beta decay or dark matter are based on xenon. Current experiments are on the tonne scale, but future ideas also aim for even larger sizes. Here we study the potential of the isotope 131Xe to allow real-time capture measurements of solar pp-chain neutrinos, besides classical neutrino-electron scattering. Here we use improved nuclear-structure calculations to determine the cross sections of solar neutrinos on 131Xe. Our updated capture-rate estimate is (80 ± 22) SNU, with neutrino survival probabilities taken into account. According to our calculations, the 8B neutrinos are the dominant contribution to the total capture rate. Due to our more accurate…

High-Precision Q -Value Measurement Confirms the Potential of Cs 135 for Absolute Antineutrino Mass Scale Determination

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…

Measurement of the 2+--0+ ground-state transition in the ß decay of 20F

12 pags., 16 figs., 4 tabs.

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

Measurement of the 2+→0+ ground-state transition in the β decay of 20F

We report the first detection of the second-forbidden, nonunique, 2+→0+, ground-state transition in the β decay of 20F. A low-energy, mass-separated 20F+ beam produced at the IGISOL facility in Jyväskylä, Finland, was implanted in a thin carbon foil and the β spectrum measured using a magnetic transporter and a plastic-scintillator detector. The β-decay branching ratio inferred from the measurement is bβ=[0.41±0.08(stat)±0.07(sys)]×10−5 corresponding to logft=10.89(11), making this one of the strongest second-forbidden, nonunique β transitions ever measured. The experimental result is supported by shell-model calculations and has significant implications for the final evolution of stars tha…

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…

The first large-scale shell-model calculation of the two-neutrino double beta decay of $^{76}$Ge to the excited states in $^{76}$Se

Large-scale shell-model calculations were carried out for the half-lives and branching ratios of the $2\nu\beta\beta$ decay of $^{76}$Ge to the ground state and the lowest three excited states $2_1^+$, $0_2^+$ and $2_2^+$ in $^{76}$Se. In total, the wave functions of more than 10,000 intermediate $1^+$ states in $^{76}$As were calculated in a three-step procedure allowing an efficient use of the available computer resources. In the first step, 250 lowest states, below some 5 MeV of excitation energy, were calculated without truncations within a full major shell $0f_{5/2}-1p-0g_{9/2}$ for both protons and neutrons. The wave functions of the rest of the states, up to some 30 MeV, were compute…

Real-time measurements of solar $pp$ neutrinos using $^{131}$Xe

Various large-scale experiments for double beta decay or dark matter are based on xenon. Current experiments are on the tonne scale but there are also ideas to aim for even larger sizes in the future. Here we study the potential of the isotope $^{131}$Xe to allow to make real-time measurements of solar $pp$ neutrinos, besides classical neutrino-electron scattering. Improved nuclear models are used to determine the cross-section of neutrinos on $^{131}$Xe. The present calculations deviate significantly from the previous ones due to updated estimates for the excited-state contributions. The updated capture-rate estimate for $pp$ neutrinos is $(4.47\pm 0.09)\ \rm SNU$ and for all solar neutrin…

Dy159 Electron-Capture: A New Candidate for Neutrino Mass Determination

International audience; The ground state to ground state electron-capture Q value of Dy159 (3/2-) has been measured directly using the double Penning trap mass spectrometer JYFLTRAP. A value of 364.73(19) keV was obtained from a measurement of the cyclotron frequency ratio of the decay parent Dy159 and the decay daughter Tb159 ions using the novel phase-imaging ion-cyclotron resonance technique. The Q values for allowed Gamow-Teller transition to 5/2- and the third-forbidden unique transition to 11/2+ state with excitation energies of 363.5449(14) keV and 362.050(40) keV in Tb159 were determined to be 1.18(19) keV and 2.68(19) keV, respectively. The high-precision Q value of transition 3/2-…

Direct measurement of the mass difference of 72As-72Ge rules out 72As as a promising β-decay candidate to determine the neutrino mass

Preprint of paper published on Physical Review C We report the first direct determination of the ground-state to ground-state electron-capture Q-value for the 72As to 72Ge decay by measuring their atomic mass difference utilizing the double Penning trap mass spectrometer, JYFLTRAP. The Q-value was measured to be 4343.596(75) keV, which is more than a 50-fold improvement in precision compared to the value in the most recent Atomic Mass Evaluation 2020. Furthermore, the new Qvalue was found to be 12.4(40) keV (3.1 σ) lower. With the significant reduction of the uncertainty of the ground-state to ground-state Q-value value combined with the level scheme of 72Ge from γ-ray spectro…

Determining gA/gV with High-Resolution Spectral Measurements Using a LiInSe2 Bolometer

Neutrinoless double beta decay (0νββ) processes sample a wide range of intermediate forbidden nuclear transitions, which may be impacted by quenching of the axial vector coupling constant (gA/gV), the uncertainty of which plays a pivotal role in determining the sensitivity reach of 0νββ experiments. In this Letter, we present measurements performed on a high-resolution LiInSe2 bolometer in a “source = detector” configuration to measure the spectral shape of the fourfold forbidden β decay of 115In. The value of gA/gV is determined by comparing the spectral shape of theoretical predictions to the experimental β spectrum taking into account various simulated background components as well as a …

Discovery of an Exceptionally Strong β -Decay Transition of $^{20}$F and Implications for the Fate of Intermediate-Mass Stars

A significant fraction of stars between 7-11 solar masses are thought to become supernovae, but the explosion mechanism is unclear. The answer depends critically on the rate of electron capture on $^{20}$Ne in the degenerate oxygen-neon stellar core. However, due to the unknown strength of the transition between the ground states of $^{20}$Ne and $^{20}$F, it has not previously been possible to fully constrain the rate. By measuring the transition, we have established that its strength is exceptionally large and enhances the capture rate by several orders of magnitude. This has a decisive impact on the evolution of the core, increasing the likelihood that the star is (partially) disrupted b…

Direct determination of the atomic mass difference of the pairs 76As−76Se and 155Tb−155Gd rules out 76As and 155 Tb as possible candidates for electron (anti)neutrino mass measurements

The first direct determination of the ground-state–to–ground-state Q values of the β− decay 76As→76Se and the electron-capture decay 155Tb→155Gd was performed utilizing the double Penning trap mass spectrometer JYFLTRAP. By measuring the atomic mass difference of the decay pairs via the phase-imaging ion-cyclotron-resonance technique, the Q values of 76As→76Se and 155Tb→155Gd were determined to be 2959.265(74) keV and 814.94(18) keV, respectively. The precision was increased relative to earlier measurements by factors of 12 and 57, respectively. The new Q values are 1.33 keV and 5 keV lower compared to the values adopted in the most recent Atomic Mass Evaluation 2020. With the newly determi…

High-precision $Q$-value measurement confirms the potential of $^{135}$Cs for antineutrino-mass detection

The ground-state-to-ground-state $\beta$-decay $Q$-value of $^{135}\textrm{Cs}(7/2^+)\to\,^{135}\textrm{Ba}(3/2^+)$ was directly measured for the first time utilizing the Phase-Imaging Ion-Cyclotron Resonance (PI-ICR) technique at the JYFLTRAP Penning-trap setup. It is the first direct determination of this $Q$-value and its value of 268.66(30)\,keV is a factor of three more precise than the currently adopted $Q$-value in the Atomic Mass Evaluation 2016. Moreover, the $Q$-value deduced from the $\beta$-decay endpoint energy has been found to deviate from our result by approximately 6 standard deviations. The measurement confirms that the first-forbidden unique $\beta^-$-decay transition $^{…

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

High-Precision Q-Value Measurement Confirms the Potential of 135Cs for Absolute Antineutrino Mass Scale Determination

The ground-state-to-ground-state β-decay Q value of Cs135(7/2+)→Ba135(3/2+) has been directly measured for the first time. The measurement was done utilizing both the phase-imaging ion-cyclotron resonance technique and the time-of-flight ion-cyclotron resonance technique at the JYFLTRAP Penning-trap setup and yielded a mass difference of 268.66(30) keV between Cs135(7/2+) and Ba135(3/2+). With this very small uncertainty, this measurement is a factor of 3 more precise than the currently adopted Q value in the Atomic Mass Evaluation 2016. The measurement confirms that the first-forbidden unique β--decay transition Cs135(7/2+)→Ba135(11/2-) is a candidate for antineutrino mass measurements wit…

Array of cryogenic calorimeters to evaluate the spectral shape of forbidden β-decays : the ACCESS project

The ACCESS (Array of Cryogenic Calorimeters to Evaluate Spectral Shapes) project aims to establish a novel technique to perform precision measurements of forbidden β-decays, which can serve as an important benchmark for nuclear physics calculations and represent a significant background in astroparticle physics experiments. ACCESS will operate a pilot array of cryogenic calorimeters based on natural and doped crystals containing β-emitting radionuclides. In this way, natural (e.g. 113Cd and 115In) and synthetic isotopes (e.g. 99Tc) will be simultaneously measured with a common experimental technique. The array will also include further crystals optimised to disentangle the different backgro…

Measurement of the 2+→0+ ground-state transition in the β decay of F 20

| openaire: EC/H2020/654002/EU//ENSAR2 We report the first detection of the second-forbidden, nonunique, 2(+) -> 0(+), ground-state transition in the beta decay of F-20. A low-energy, mass-separated F-20(+) beam produced at the IGISOL facility in Jyvaskyla, Finland, was implanted in a thin carbon foil and the beta spectrum measured using a magnetic transporter and a plastic-scintillator detector. The beta-decay branching ratio inferred from the measurement is b(beta) = [0.41 +/- 0.08(stat) +/- 0.07(sys)] x 10(-5) corresponding to log ft = 10.89(11), making this one of the strongest second-forbidden, nonunique beta transitions ever measured. The experimental result is supported by shell-mode…

Measurement of the 2 + → 0 + ground-state transition in the β decay of F 20

Measurement of the Spectral Shape of the β -Decay of Xe137 to the Ground State of Cs137 in EXO-200 and Comparison with Theory

We report on a comparison between the theoretically predicted and experimentally measured spectra of the first-forbidden nonunique β-decay transition ^{137}Xe(7/2^{-})→^{137}Cs(7/2^{+}). The experimental data were acquired by the EXO-200 experiment during a deployment of an AmBe neutron source. The ultralow background environment of EXO-200, together with dedicated source deployment and analysis procedures, allowed for collection of a pure sample of the decays, with an estimated signal to background ratio of more than 99 to 1 in the energy range from 1075 to 4175 keV. In addition to providing a rare and accurate measurement of the first-forbidden nonunique β-decay shape, this work constitut…

Novel Penning-trap techniques reveal isomeric states in $^{128}$In and $^{130}$In for the first time

Isomeric states in $^{128}$In and $^{130}$In have been studied with the JYFLTRAP Penning trap at the IGISOL facility. By employing novel ion manipulation techniques, different states were separated and masses of six beta-decaying states were measured. JYFLTRAP was also used to select the ions of interest for identification at a post-trap decay spectroscopy station. A new beta-decaying high-spin isomer feeding the $15^-$ isomer in $^{128}$Sn has been discovered in $^{128}$In at $1797.6(20)$ keV. Shell-model calculations employing a CD-Bonn potential re-normalized with the perturbative G-matrix approach suggest this new isomer to be a $16^+$ spin-trap isomer. In $^{130}$In, the lowest-lying $…

Dy 159 Electron-Capture: A New Candidate for Neutrino Mass Determination

Discovery of an Exceptionally Strong β -Decay Transition of F 20 and Implications for the Fate of Intermediate-Mass Stars

Three beta-decaying states in In and In resolved for the first time using Penning-trap techniques

Isomeric states in $^{128}$In and $^{130}$In have been studied with the JYFLTRAP Penning trap at the IGISOL facility. By employing state-of-the-art ion manipulation techniques, three different beta-decaying states in $^{128}$In and $^{130}$In have been separated and their masses measured. JYFLTRAP was also used to select the ions of interest for identification at a post-trap decay spectroscopy station. A new beta-decaying high-spin isomer feeding the 15− isomer in $^{128}$Sn has been discovered in $^{128}$In at 1797.6(20) keV. Shell-model calculations employing a CD-Bonn potential re-normalized with the perturbative G-matrix approach suggest this new isomer to be a 16+ spin-trap isomer. In …

Direct determination of the atomic mass difference of the pairs As76−Se76 and Tb155−Gd155 rules out As76 and Tb155 as possible candidates for electron (anti)neutrino mass measurements

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…

Direct measurement of the mass difference of As 72 − Ge 72 rules out As 72 as a promising β -decay candidate to determine the neutrino mass

Dy159 Electron-Capture: A New Candidate for Neutrino Mass Determination

Measurement of the Spectral Shape of the beta-decay of 137Xe to the Ground State of 137Cs in EXO-200 and Comparison with Theory

We report on a comparison between the theoretically predicted and experimentally measured spectra of the first-forbidden non-unique $\beta$-decay transition $^{137}\textrm{Xe}(7/2^-)\to\,^{137}\textrm{Cs}(7/2^+)$. The experimental data were acquired by the EXO-200 experiment during a deployment of an AmBe neutron source. The ultra-low background environment of EXO-200, together with dedicated source deployment and analysis procedures, allowed for collection of a pure sample of the decays, with an estimated signal-to-background ratio of more than 99-to-1 in the energy range from 1075 to 4175 keV. In addition to providing a rare and accurate measurement of the first-forbidden non-unique $\bet…