arXiv subjects

T. Eronen

Publications and source records attributed to T. Eronen.

At least 19 recordsLinked to original sources

arXiv2026

Island of Inversion in neutron-rich cobalt isotopes revealed from mass measurements

Mass measurements of the ground and isomeric states of $^{68-70}$Co have been performed using the JYFLTRAP Penning-trap mass spectrometer at the IGISOL facility. The masses were measured, either for the first time for the isomeric states of $^{68}$Co and $^{70}$Co, or with greatly improved precision for the others, removing ambiguities in the mass surface beyond $N=40$. The ordering of the low and high-spin states in $^{68}$Co and $^{70}$Co has also been established. The results, supported by Large-Scale Shell Model and Discrete Non-Orthogonal Shell-Model calculations, show a gradual lowering of intruder states with increasing neutron number, eventually leading to an inversion in $^{70}$Co. These findings clarify previously proposed contradictory interpretations. Finally, we demonstrate the importance of including induced effective 3N forces for a consistent description of binding energies in the island of inversion near $N=40$.

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arXiv2026

Study of $\boldsymbol{\beta}$ Decay Shape Factors in First-Forbidden Transitions with $\boldsymbol{\Delta I^\pi = 0^-}$ for Reactor Antineutrino Spectra Predictions

The electron spectra of the $\beta$ decays of $^{92}$Rb and $^{142}$Cs, key contributors to the reactor antineutrino spectrum, were measured at the IGISOL facility using radioactive beams of high isotopic purity. The shapes of the measured $\beta$ spectra were compared with various $\beta$ shape models, including first-forbidden correction factors for $\Delta I^\pi = 0^-$ ground-state to ground-state transitions. Comparisons with previous experimental results are also provided. The shapes of the newly measured $\beta$ spectra are well reproduced employing feedings extracted from total absorption gamma spectroscopy measurements.

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arXiv2025

High-resolution multi-reflection time-of-flight mass spectrometer for exotic nuclei at IGISOL

A Multi-Reflection Time-of-Flight Mass Spectrometer (MR-ToF-MS) has been commissioned at the Ion-Guide Isotope Separator On-Line (IGISOL) facility. It consists of six electrode pairs that form a nearly energy-isochronous potential and a pulsed drift-tube to trap the ions between the electrodes. Time-of-flight peak widths down to 22 ns full-width at half-maximum and mass-resolving powers of $\approx 1.5 \times 10^5$ within 20 ms have been demonstrated. The obtained time-focus and mass-resolving power depend sensitively on the trapping energy, energy spread and the number of revolutions of the ions. The mass-resolving power is affected by the temporal and energy spread of the ions entering the MR-ToF-MS, and fluctuations in the electrode voltages due to temperature variations. The longitudinal emittance corresponding to the temporal and energy spread of $^{39}$K is estimated to be 175 eVns based on the data, close to the expected 186(10) eVns. The time-of-flight temperature sensitivity is found to be -5.55(30) ppm/K. In addition to atomic mass measurements of short-lived exotic nuclides, the MR-ToF-MS can be used as a fast mass separator for various other experiments at IGISOL and as an ion counter for laser spectroscopy and yield measurements.

physics.ins-det↗

arXiv2025

Probing the quantum phase transition around $N\approx60$ via mass measurements of technetium isotopes

The masses of neutron-rich $^{104-106}$Tc isotopes were measured using the JYFLTRAP double Penning trap and found to deviate from the Atomic Mass Evaluation 2020 by $-79(25)$, $40(12)$ and $94(41)$ keV, respectively. In the case of $^{105,106}$Tc, the updated $Q_\beta$ values are in agreement with a previous JYFLTRAP measurement, disagreeing with the values from the mass evaluation. The new mass values result in a more linear trend in two-neutron separation energies indicating that technetium ($Z=43$) isotopes around $N \approx 60$ are not a part of the island of shape coexistence around $^{100}$Zr$_{60}$.

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arXiv2025

Study of beta spectrum shapes relevant to the prediction of reactor antineutrino spectra

The shapes of the beta spectra of 92Rb and 142Cs, two of the beta decays most relevant for the prediction of the antineutrino spectrum in reactors, have been measured. A new setup composed of two dE-E telescopes has been used. High purity radioactive beams of the isotopes of interest were provided by the IGISOL facility using the JYFLTRAP double Penning trap. The resulting beta spectra have been compared with model predictions using beta decay feedings from total absorption gamma spectroscopy measurements and shape corrections employed in the calculation of the antineutrino spectrum, validating both further. The procedure can be extended to other relevant nuclei in the future, providing solid ground for the prediction of the antineutrino spectrum in reactors.

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arXiv2025

Performance of the MORA Apparatus for Testing Time-Reversal Invariance in Nuclear Beta Decay

The MORA experimental setup is designed to measure the triple-correlation D parameter in nuclear beta decay. The D coefficient is sensitive to possible violations of time-reversal invariance. The experimental configuration consists of a transparent Paul trap surrounded by a detection setup with alternating beta and recoil-ion detectors. The octagonal symmetry of the detection setup optimizes the sensitivity of positron-recoil-ion coincidence rates to the D correlation, while reducing systematic effects. MORA utilizes an innovative in-trap laser polarization technique. The design and performance of the ion trap, associated beamline elements, lasers and beta and recoil-ion detectors, are presented. Recent progress towards the polarization proof-of-principle is described.

physics.ins-det↗

arXiv2025

HIBISCUS: a new ion beam radio-frequency quadrupole cooler-buncher for high-precision experiments with exotic radioactive ions

HIBISCUS (Helium-Inflated Beam Improvement Setup that Cools and Undermines Spreads), a new radiofrequency quadrupole cooler-buncher device has been developed and commissioned offline at the Ion Guide Isotope Separator On-Line (IGISOL) facility in Jyv\"askyl\"a in Finland, as an in-kind contribution for the Facility for Antiproton and Ion Research facility. HIBISCUS improves the ion optical properties of incident low-energy 6~keV beams with the option to have it ultimately extracted in temporally short bunches ($<1$~$\mu$s). This paper provides technical descriptions of its main characteristics, along with a set of optimum working parameters and performance in terms of transmission efficiency, longitudinal energy spread of the cooled ions and temporal width of the extracted bunches.

physics.acc-ph↗

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, Jyv\"askyl\"a, 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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arXiv2024

Discovery of a new long-lived isomer in $^{114}$Rh via Penning-trap mass spectrometry

We report on mass measurements of three long-lived states in $^{114}$Rh performed with the JYFLTRAP Penning-trap mass spectrometer: the ground state and two isomers with estimated half-lives of about one second. The used Phase-Imaging Ion-Cyclotron-Resonance technique allowed for the discovery of a so far unknown second long-lived isomer. All three states were produced directly in proton-induced fission on a uranium target, whereas only the isomeric states were populated in the $\beta$ decay of the $^{114}$Ru ground state with spin-parity $0^+$. We propose spin-parity assignments of $(6^-)$ for the ground state, and $(3^+)$ and $(0^-)$ for the isomers. They resolve the puzzle of anomalous fission yields of this isotope despite the existing literature assigning a low angular momentum to the ground state. The experimental evidence is further supported by a detailed analysis based on mean-field calculations with the BSkG3 model. As for many other nuclei in this mass region, considering triaxial shapes is decisive for the interpretation of low-lying states of this nucleus. The discovery of a new isomer in $^{114}$Rh and our theoretical work challenge the currently adopted spin-parity assignments in this and several other odd-odd neutron-rich Rh isotopes.

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arXiv2024

Ultra-low $Q_\beta$ value for the allowed decay of $^{110}$Ag$^m$ confirmed via mass measurements

The mass of the electron-antineutrino can be determined in dedicated measurements of the $\beta$ spectral shape near the $\beta$ endpoint of a $\beta^-$ transition, with a low $Q$ value enhancing the sensitivity of the measurement. One such low-$Q$-value candidate is the transition between the $6^+$ isomer of $^{110}$Ag and the $5^+_2$ state in $^{110}$Cd ($Q^{\ast}_{\beta,m}=-0.12(131)$ keV). To reduce the uncertainty of the $Q$ value, we have used the phase-imaging ion-cyclotron-resonance technique with the JYFLTRAP double Penning trap and performed a high-precision atomic-mass measurement of $^{109}$Ag with $^{110}$Cd as a reference. Combined with the known spectroscopic data, we obtain a re-evaluated value $Q^{\ast}_{\beta,m}=405(135)$ eV, for the $^{110}\text{Ag}(6^+_\text{m}) \rightarrow {^{110}\text{Cd}}(5^+_2)$ transition. This represents the lowest $Q_{\beta}$ value for any allowed transition observed to date. In order to estimate the partial half-life ($t_{1/2}$) and branching ratio (Br) of the transition, nuclear shell-model calculations were performed using the $jj45pnb$ Hamiltonian in combination with state-of-the-art atomic calculations. The computed values $t_{1/2} = 2.23^{+5.24}_{-1.28} \times 10^7$ years and $\textrm{Br} = 3.07^{+4.16}_{-2.15} \times 10^{-8}$, along with the thermal-neutron capture on stable $^{109}$Ag as a viable production method, make $^{110}\textrm{Ag}^m$ a promising candidate for future antineutrino-mass measurements.

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arXiv2024

High-precision mass measurements of the ground and isomeric states in $^{124,125}$Ag

The masses of the ground and isomeric states in $^{124,125}$Ag have been measured using the phase-imaging ion-cyclotron-resonance technique at the JYFLTRAP double Penning trap mass spectrometer. The ground states of $^{124}$Ag and $^{125}$Ag were found to be 30(250) keV and 250(430) keV less bound but 36 and 110 times more precise than in the Atomic Mass Evaluation 2020, respectively. The excitation energy of $^{124}$Ag$^{m}$, ${E_x = 188.2(25)}$ keV, was determined for the first time. The new precise mass values have been utilised to study the evolution of nuclear structure via two-neutron separation energies. The impact on the astrophysical rapid neutron capture process has been investigated via neutron-capture reaction rate calculations. The precision measurements indicate a more linear trend in two-neutron separation energies and reduce the mass-related uncertainties for the neutron-capture rate of $^{124}$Ag$(n,\gamma)^{125}$Ag by a factor of around 100. The new mass values also improve the mass of $^{123}$Pd, previously measured using $^{124}$Ag as a reference.

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arXiv2024

Prominent bump in the two-neutron separation energies of neutron-rich lanthanum isotopes revealed by high-precision mass spectrometry

We report on high-precision atomic mass measurements of $^{148\text{-}153}$La and $^{151}$Ce performed with the JYFLTRAP double Penning trap using the Phase-Imaging Ion-Cyclotron-Resonance technique. The masses of $^{152,153}$La were experimentally determined for the first time. We confirm the sharp kink in the two-neutron separation energies at the neutron number ${N=93}$ in the cerium (${Z=58}$) isotopic chain. Our precision mass measurements of the most exotic neutron-rich lanthanum (${Z=57}$) isotopes reveal a sudden increase in two-neutron separation energies from ${N=92}$ to ${N=93}$. Unlike in the cerium isotopic chain, the kink is not sharp but extends to ${N=94}$ forming a prominent bump. The gain in energy is about 0.4 MeV, making it one of the strongest changes in two-neutron separation energies over the whole chart of nuclides, away from nuclear shell closures. The results call for further studies to elucidate the structure of neutron-rich lanthanum isotopes.

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arXiv2024

Probing the N=104 midshell region for the r process via precision mass spectrometry of neutron-rich rare-earth isotopes with the JYFLTRAP double Penning trap

We have performed high-precision mass measurements of neutron-rich rare-earth Tb, Dy and Ho isotopes using the Phase-Imaging Ion-Cyclotron-Resonance technique at the JYFLTRAP double Penning trap. We report on the first experimentally determined mass values for $^{169}$Tb, $^{170}$Dy and $^{171}$Dy, as well as the first high-precision mass measurements of $^{169}$Dy and $^{169\text{-}171}$Ho. For $^{170}$Ho, the two long-lived ground and isomeric states were resolved and their mass measured, yielding an isomer excitation energy of $E_\text{exc}=150.8(54)$~keV. In addition, we have performed independent crosschecks of previous Penning-trap values obtained for $^{167\text{,} 168}$Tb and $^{167\text{,} 168}$Dy. We have extended the systematics of two-neutron separation energies to the neutron midshell at $N=104$ in all of the studied isotopic chains. Our updated and new mass measurements provide better mass-related constraints for the neutron-capture reaction rates relevant to the astrophysical rapid neutron capture (r) process. The r-process abundances calculated with the new mass values seem to produce a steeper minimum at A=170 and differ by around 15-30\% from the abundances computed with the Atomic Mass Evaluation 2020 values.

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arXiv2024

Comment on "Spin-trap isomers in deformed, odd-odd nuclei in the light rare-earth region near $N=98$"

A new isomeric $(4^-)$ state at 285.5(32) keV in $^{162}$Tb was reported by R. Orford et al. [Phys. Rev. C 102, 011303(R) (2020)] based on a Penning-trap mass measurement. Here we show that this result is not compatible with existing experimental data. The state identified as $^{162}$Tb$^{m}$ with a mass-excess value of $-65593.9(25)$ keV is actually the $1^-$ ground state. The state identified as the ground state of $^{162}$Tb is most likely a molecular contaminant with the same mass-over-charge ratio.

nucl-th↗

arXiv2024

Isomeric states of fission fragments explored via Penning trap mass spectrometry at IGISOL

The masses of $^{84}$Br, $^{105}$Mo, $^{115,119,121}$Pd, $^{122}$Ag, $^{127,129}$In, $^{132}$Sb and their respective isomeric states have been measured with the JYFLTRAP Penning trap mass spectrometer using the phase-imaging ion-cyclotron-resonance technique. The excitation energies of the isomeric states in $^{132}$Sb and $^{119}$Pd were experimentally determined for the first time, while for $^{84}$Br, $^{115}$Pd and $^{127,129}$In, the precision of the mass values was substantially improved. In $^{105}$Mo and $^{121}$Pd there were no signs of a long-lived isomeric state. The ground-state measurements of $^{119}$Pd and $^{122}$Ag indicated that both are significantly more bound than the literature values. For $^{122}$Ag, there was no indication of a proposed third long-lived state. The results for the $N=49$ nucleus $^{84}$Br and isomers close to doubly magic $^{132}$Sn have been compared to the shell-model and the microscopic quasiparticle-phonon model calculations.

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arXiv2024

Precision mass measurements in the zirconium region pin down the mass surface across the neutron midshell at $N=66$

Precision mass measurements of $^{104}$Y, $^{106}$Zr, $^{104,104m,109}$Nb, and $^{111,112}$Mo have been performed with the JYFLTRAP double Penning trap mass spectrometer at the Ion Guide Isotope Separator On-Line facility. The order of the long-lived states in $^{104}$Nb was unambiguously established. The trend in two-neutron separation energies around the $N=66$ neutron midshell appeared to be steeper with respect to the Atomic Mass Evaluation 2020 extrapolations for the $_{39}$Y and $_{40}$Zr isotopic chains and less steep for the $_{41}$Nb chain, indicating a possible gap opening around $Z=40$. The experimental results were compared to the BSkG2 model calculations performed with and without vibrational and rotational corrections. All of them predict two low-lying minima for $^{106}$Zr. While the unaltered BSkG2 model fails to predict the trend in two-neutron separation energies, selecting the more deformed minima in calculations and removing the vibrational correction, the calculations are more in line with experimental data. The same is also true for the $2^+_1$ excitation energies and differences in charge radii in the Zr isotopes. The results stress the importance of improved treatment of collective corrections in large-scale models and further development of beyond-mean-field techniques.

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arXiv2024

Direct high-precision measurement of the mass difference of $^{77}$As-$^{77}$Se related to neutrino mass determination

The first direct determination of the ground-state-to-ground-state ${\beta^{-}}$-decay $Q$-value of $^{77}$As to $^{77}$Se was performed by measuring their atomic mass difference utilizing the double Penning trap mass spectrometer, JYFLTRAP. The resulting $Q$-value is 684.463(70) keV, representing a remarkable 24-fold improvement in precision compared to the value reported in the most recent Atomic Mass Evaluation (AME2020). With the significant reduction of the uncertainty of the ground-state-to-ground-state $Q$-value and knowledge of the excitation energies in $^{77}$Se from $\gamma$-ray spectroscopy, the ground-state-to-excited-state $Q$-value of the transition $^{77}$As (3/2$^{-}$, ground state) $\rightarrow$ $^{77}$Se$^{*}$ (5/2$^{+}$, 680.1035(17) keV) was refined to be 4.360(70) keV. We confirm that this potential low $Q$-value ${\beta^{-}}$-decay transition for neutrino mass determination is energetically allowed at a confidence level of about 60$\sigma$. Nuclear shell-model calculations with two well-established effective Hamiltonians were used to estimate the partial half-life for the low $Q$-value transition. The half-life was found to be of the order of 10$^{9}$ years for this first-forbidden non-unique transition, which rules out this candidate a potential source for rare-event experiments searching for the electron antineutrino mass.

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arXiv2024

Long-sought isomer turns out to be the ground state of $^{76}$Cu

Isomers close to the doubly magic nucleus $^{78}$Ni ($Z=28$, $N=50$) provide essential information on the shell evolution and shape coexistence far from stability. The existence of a long-lived isomeric state in $^{76}$Cu has been debated for a long time. We have performed high-precision mass measurements of $^{76}$Cu with the JYFLTRAP double Penning trap mass spectrometer at the Ion Guide Isotope Separator On-Line facility and confirm the existence of such a isomeric state with an excitation energy $E_x=64.8(25)$ keV. Based on the ratio of detected ground- and isomeric-state ions as a function of time, we show that the isomer is the shorter-living state previously considered as the ground state of $^{76}$Cu. The result can potentially change the conclusions made in previous works related to the spin-parity and charge radius of the $^{76}$Cu ground state. Additionally, the new $^{76}$Cu$(n,\gamma)$ reaction $Q$-value has an impact on the astrophysical rapid neutron-capture process.

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