arXiv subjects

A. P. Weaver

Publications and source records attributed to A. P. Weaver.

7 recordsLinked to original sources

arXiv2026

Mass measurements of $^{179-184}$Yb identify an anomalous proton-neutron interaction

Mass measurements of nuclei can identify structurally-driven trends in binding energy across isotopic chains, and can also isolate specific nucleon-nucleon interactions, such as the $δV_{\mathrm{pn}}$ interaction of the last two valence protons with the last two valence neutrons. Below $^{208}$Pb, investigation of the local binding energy and $δV_{\mathrm{pn}}$ systematics can facilitate a better understanding of the behaviour of the proton-neutron interaction in the 'hole-hole' regime (where valence interactions can be modelled in hole-space rather than particle-space) and provide insight on the potential onset of a prolate-to-oblate shape transition. However, measurement of the necessary nuclei has been exceptionally challenging. Here we present six first-time measurements of neutron-rich ytterbium, using advanced rare isotope production and mass spectrometry techniques, leading to the identification of an anomalously strong proton-neutron interaction in the 'hole-hole' quadrant below $^{208}$Pb. The scale of this interaction, at $^{186}$Hf, is comparable to that of similar signals at doubly-magic nuclei and shape transitions. The experimental results are compared with contemporary mean-field model predictions, that do not accurately reproduce the anomaly. The results are also used to benchmark predictions from several models, to facilitate more accurate descriptions towards a key r-process waiting point at $N = 126$.

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arXiv2024

Binding energies, charge radii, spins and moments: odd-odd Ag isotopes and discovery of a new isomer

We report on the masses and hyperfine structure of ground and isomeric states in $^{114,116,118,120}$Ag isotopes, measured with the phase-imaging ion-cyclotron-resonance technique (PI-ICR) with the JYFLTRAP mass spectrometer and the collinear laser spectroscopy beamline at the Ion Guide Isotope Separator On-Line (IGISOL) facility, Jyväskylä, Finland. We measured the masses and excitation energies, electromagnetic moments, and charge radii, and firmly established the nuclear spins of the long-lived states. A new isomer was discovered in $^{118}$Ag and the half-lives of $^{118}$Ag long-lived states were reevaluated. We unambiguously pinned down the level ordering of all long-lived states, placing the inversion of the $I = 0^-$ and $I = 4^+$ states at $A = 118$ $(N = 71)$. Lastly, we compared the electromagnetic moments of each state to empirical single-particle moments to identify the dominant configuration where possible.

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arXiv2023

Binding energies of ground and isomeric states in neutron-rich ruthenium isotopes: measurements at JYFLTRAP and comparison to theory

We report on precision mass measurements of $^{113,115,117}$Ru performed with the JYFLTRAP double Penning trap mass spectrometer at the Accelerator Laboratory of University of Jyväskylä. The phase-imaging ion-cyclotron-resonance technique was used to resolve the ground and isomeric states in $^{113,115}$Ru and enabled for the first time a measurement of the isomer excitation energies, $E_x(^{113}$Ru$^{m})=100.5(8)$ keV and $E_x(^{115}$Ru$^{m})=129(5)$ keV. The ground state of $^{117}$Ru was measured using the time-of-flight ion-cyclotron-resonance technique. The new mass-excess value for $^{117}$Ru is around 36 keV lower and 7 times more precise than the previous literature value. With the more precise ground-state mass values, the evolution of the two-neutron separation energies is further constrained and a similar trend as predicted by the BSkG1 model is obtained up to the neutron number $N=71$.

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arXiv2022

Odd-odd neutron-rich rhodium isotopes studied with the double Penning trap JYFLTRAP

Precision mass measurements of neutron-rich rhodium isotopes have been performed at the JYFLTRAP Penning trap mass spectrometer at the Ion Guide Isotope Separator On-Line (IGISOL) facility. We report results on ground- and isomeric-state masses in $^{110,112,114,116,118}$Rh and the very first mass measurement of $^{120}$Rh. The isomeric states were separated and measured for the first time using the phase-imaging ion-cyclotron-resonance (PI-ICR) technique. For $^{112}$Rh, we also report new half-lives for both the ground state and the isomer. The results are compared to theoretical predictions using the BSkG1 mass model and discussed in terms of triaxial deformation.

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arXiv2022

Direct determination of the atomic mass difference of the pairs $^{76}$As-$^{76}$Se and $^{155}$Tb-$^{155}$Gd rules out $^{76}$As 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 $^{76}$As $\rightarrow$ $^{76}$Se and the electron-capture decay $^{155}$Tb $\rightarrow$ $^{155}$Gd 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 (PI-ICR) technique, the $Q$ values of $^{76}$As $\rightarrow$ $^{76}$Se and $^{155}$Tb $\rightarrow$ $^{155}$Gd 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 determined ground-state-to-ground-state $Q$ values combined with the excitation energy from $γ$-ray spectroscopy, the $Q$ values for ground-state-to-excited-state transitions $^{76}$As (ground state) $\rightarrow$ $^{76}$Se$^*$ (2968.4(7) keV) and $^{155}$Tb (ground state) $\rightarrow$ $^{155}$Gd$^*$ (815.731(3) keV) were derived to be -9.13(70) keV and -0.79(18) keV. Thus we have confirmed that both of the $β^{-}$-decay and EC-decay candidate transitions are energetically forbidden at a level of at least 4$σ$, thus definitely excluding these two cases from the list of potential candidates for the search of low-$Q$-value $β^-$ or EC decays to determine the electron-(anti)neutrino mass.

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arXiv2021

$^{159}$Dy electron-capture: a strong new candidate for neutrino mass determination

{ The ground-state to ground-state electron-capture $Q$ value of $^{159}$Dy ($3/2^-$) has been measured directly utilizing 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 $^{159}$Dy and the decay daughter $^{159}$Tb 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 $^{159}$Tb were determined to be 1.18(19) keV and 2.68(19) keV, respectively. The high-precision $Q$ value of transition $3/2^-\to 5/2^-$ from this work, revealing itself as the lowest electron-capture $Q$ value, is utilized to unambiguously characterise all the possible lines that are present in its electron capture spectrum. { We performed atomic many-body calculations for both transitions to determine electron-capture probabilities from various atomic orbitals, and found an order of magnitude enhancement in the event rates near the end-point of energy spectrum in the transition to the $5/2^-$ nuclear excited state, which can become very interesting once the experimental challenges of identifying decays into excited states are overcome. The transition to the $11/2^+$ state is strongly suppressed and found unsuitable for measuring the neutrino mass. These results show that the electron capture in the $^{159}$Dy atom, going to the $5/2^-$ state of the $^{159}$Tb nucleus, %\textcolor{red} {is a new candidate which may open the way to determine the electron-neutrino mass in the sub-eV region by studying EC. Further experimental feasibility studies, including coincidence measurements with realistic detectors, will be of great interest.} }

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arXiv2021

Direct measurement of the mass difference of $^{72}$As-$^{72}$Ge rules out $^{72}$As as a promising $β$-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 $σ$) lower. With the significant reduction of the uncertainty of the ground-state to ground-state $Q$-value value combined with the level scheme of $^{72}$Ge from $γ$-ray spectroscopy, we confirm that the five potential ultra-low $Q$-value ${β^{+}}$-decay or electron capture transitions are energetically forbidden, thus precluding all the transitions as possible candidates for the electron neutrino mass determination. However, the discovery of small negative $Q$-values opens up the possibility to use $^{72}$As for the study of virtual $β$-$γ$ transitions.

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