arXiv subjects

Anu Kankainen

Publications and source records attributed to Anu Kankainen.

10 recordsLinked to original sources

arXiv2026

Precise determination of electron-capture $Q$ value of $^{113}$Sn decay related to electron neutrino mass measurements

A high-precision measurement of the electron-capture (EC) decay $Q$ value for the ground-state-to-ground-state (gs-to-gs) transition of $^{113}$Sn to $^{113}$In has been performed using the JYFLTRAP double Penning trap mass spectrometer. Employing the phase-imaging ion-cyclotron-resonance technique, the isomeric state of $^{113}$Sn at 77.389(19) keV was resolved, and the cyclotron frequency ratio measured between the isomer $^{113m}$Sn and the daughter nucleus $^{113}$In. This yielded an isomer-to-ground-state $Q$ value of 1116.64(19) keV and gs-to-gs $Q$ value of 1039.25(19) keV. The atomic mass excess of $^{113}$Sn was determined as $-$88327.87(27) keV/c$^2$, in excellent agreement with the Atomic Mass Evaluation 2020 (AME2020) but with a sixfold precision improvement. Using nuclear energy-level data for $^{113}$In, we identified two low $Q$-value transitions of the ground state of $^{113}$Sn to excited states of $^{113}$In at 1024.280(50) keV ($Q_{EC}^* = 14.97(20)$ keV, second forbidden non-unique) and 1029.650(50) keV ($Q_{EC}^* = 9.60(20)$ keV, allowed). The allowed transition exhibits small energy differences ($\Delta_{L1} = 5.58(20)$ keV, $\Delta_{L2} = 5.87(20)$ keV) from L1 and L2 shell binding energies, enhancing endpoint events. Partial half-lives and energy-release spectra were calculated using the self-consistent Dirac-Hartree-Fock-Slater (DHFS) method (including exchange, overlap, shake-up, and shake-off corrections) together with the nuclear shell model, show enhanced endpoint sensitivity for the allowed transition to the state at 1029.650 keV. Including subthreshold atomic states in the spectral function enhances the EC rate near the zero-neutrino-momentum region by a factor of five, enabling new approaches for low $Q$-value EC reactions in neutrino-mass studies.

nucl-ex↗

arXiv2025

High-precision direct decay energy measurements of the electron-capture decay of $^{97}$Tc

A direct measurement of the ground-state-to-ground-state electron-capture decay $Q$ ($Q_{\rm EC}$) value of $^{97}$Tc has been conducted employing the high resolving power phase-imaging ion-cyclotron-resonance technique with the double Penning trap mass spectrometer JYFLTRAP. The resulting $Q_{\rm EC}$ value for $^{97}$Tc is 324.82(21) keV, exhibiting a precision approximately 19 times higher than the value adopted in the newest Atomic Mass Evaluation (AME2020) and differing by 1.2$σ$. Furthermore, by combining this refined $Q$ value with nuclear energy-level data for the decay-daughter $^{97}$Mo, a potential ultra-low Q-value transition, possibly of allowed type, $^{97}$Tc (9/2$^{+}$, ground state) $\rightarrow$ $^{97}$Mo$^{*}$ (320(1) keV), was evaluated for future long-term neutrino-mass determination experiments. The ground-state-to-excited-state electron-capture decay $Q$ value ($Q^{*}_{\rm EC}$) of this transition was determined to be 4.8(10) keV, confirming it to be energetically allowed with a confidence level of exceeding 4$σ$. The captures of electrons occupying the L and higher shells for this transition are energetically allowed, giving a value of 2.0(10) keV for the closest distance of $Q^{*}_{\rm EC}$ to the allowed binding energy of the L1 shell. To predict partial half-lives and energy-release distributions for this transition, the atomic self-consistent many-electron Dirac--Hartree--Fock--Slater method and the nuclear shell model have been employed. Dominant correction terms such as exchange and overlap corrections, as well as shake-up and shake-off effects, were included in the final results. Moreover, the normalized distribution of released energy in the electron-capture decay of $^{97}$Tc to excited states of $^{97}$Mo, is compared with that of $^{163}$Ho, which is being used for electron-neutrino-mass determination.

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arXiv2025

Isomeric yield ratios and mass spectrometry of Y and Nb isotopes in the neutron-rich N=60 region: the unusual case of $^{98}$Y

The isomeric yield ratio (IYR) of fission products is an observable that carries relevant information about the fragments emerging from the scission of a fissioning nucleus. We report on IYR of $^{96,98,100}$Y and $^{100,102}$Nb, together with the previously reported values for $^{97}$Y and $^{99}$Nb, produced in the 28 MeV $α$-induced fission of $^{232}$Th at the Ion Guide Isotope Separation On-Line (IGISOL) facility of the University of Jyv{ä}skyl{ä}. We measured the IYR using two different techniques, the phase-imaging ion-cyclotron-resonance (PI-ICR) and the multiple-reflection time-of-flight mass spectrometry (MR-TOF-MS) methods. Moreover, we measured the masses of the long-lived states in $^{98,100}$Y and $^{100,102}$Nb populated via in-trap $β$-decay of their precursors. Since the $β$-decay selectively populates states with a favourable spin-parity, we could identify the measured state and show that the ground state is the low-spin state in the cases of $^{98}$Y and $^{100}$Nb, while it is the high-spin state in the cases of $^{100}$Y and $^{102}$Nb. This measurement confirms the spin-parity assignments of all the nuclei as they are reported in the NUBASE2020 evaluations, disagreeing with the assignment for $^{100}$Y reported in the ENSDF evaluation. Making also use of previously reported data, we observe an anomalously low IYR for the $N=59$ isotope $^{98}$Y as compared to other yttrium or neighboring niobium isotopes. This behavior is very rare across the nuclear chart and is posited to be connected to the characteristic shape coexistence of $^{98}$Y, and to the change in the charge radii of the ground and excited states in the $N=58-60$ region.

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arXiv2025

Disentangling the influence of excitation energy and compound nucleus angular momentum on fission fragment angular momentum

The origin of the large angular momenta observed for fission fragments is still a question under discussion. To address this, we study isomeric yield ratios (IYR), i.e. the relative population of two or more long-lived metastable states with different spins, of fission products. We report on IYR of 17 isotopes produced in the 28 MeV $α$-induced fission of $^{232}$Th at the IGISOL facility of the University of Jyväskylä. The fissioning nuclei in this reaction are $^{233,234,235}$U*. We compare our data to IYR from thermal neutron-induced fission of $^{233}$U and $^{235}$U, and we observe statistically significant larger IYR in the $^{232}$Th($α$,f) reaction, where the average compound nucleus (CN) spin is 7.5 $\hbar$, than in $^{233,235}$U(n$_{th}$,f), with average spins 2.5 and 3.5 $\hbar$, respectively. To assess the influence of the excitation energy, we study literature data of IYR from photon-induced fission reactions, and find that the IYR are independent of the CN excitation energy. We conclude that the different IYR must be explained by the different CN spin alone. This implies that the FF angular momentum only partly comes from the fission process itself, and is in addition influenced by the angular momentum present in the CN.

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arXiv2024

High-precision measurement of the atomic mass of $^{84}$Sr and implications to isotope shift studies

The absolute mass of $^{84}$Sr was determined using the phase-imaging ion-cyclotron-resonance technique with the JYFLTRAP double Penning trap mass spectrometer. A more precise value for the mass of $^{84}$Sr is essential for providing potential indications of physics beyond the Standard Model through high-precision isotope shift measurements of Sr atomic transition frequencies. The mass excess of $^{84}$Sr was refined to be -80649.229(37) keV/c$^2$ from high-precision cyclotron-frequency-ratio measurements with a relative precision of 4.8$\times$10$^{-10}$. The obtained mass-excess value is in agreement with the adopted value in the Atomic Mass Evaluation 2020, but is 30 times more precise. With this new value, we confirm the previously observed nonlinearity in the study of the isotope shift of strontium. Moreover, the double-beta ($2β^{+}$) decay $Q$ value of $^{84}$Sr was directly determined to be 1790.115(37) keV, and the precision was improved by a factor of 30.

nucl-ex↗

arXiv2024

High-precision mass measurements of neutron deficient silver isotopes probe the robustness of the $N$ = 50 shell closure

High-precision mass measurements of exotic $^{95-97}$Ag isotopes close to the $N = Z$ line have been conducted with the JYFLTRAP double Penning trap mass spectrometer, with the silver ions produced using the recently commissioned inductively-heated hot cavity catcher laser ion source at the Ion Guide Isotope Separator On-Line facility. The atomic mass of $^{95}$Ag was directly determined for the first time. In addition, the atomic masses of $β$-decaying 2$^+$ and 8$^+$ states in $^{96}$Ag have been identified and measured for the first time, and the precision of the $^{97}$Ag mass has been improved. The newly measured masses, with a precision of $\approx$ 1 keV/c$^2$, have been used to investigate the $N =$ 50 neutron shell closure confirming it to be robust. Empirical shell-gap and pairing energies determined with the new ground-state mass data are compared with the state-of-the-art \textit{ab initio} calculations with various chiral effective field theory Hamiltonians. The precise determination of the excitation energy of the $^{96m}$Ag isomer in particular serves as a benchmark for \textit{ab initio} predictions of nuclear properties beyond the ground state, specifically for odd-odd nuclei situated in proximity to the proton dripline below $^{100}$Sn. In addition, density functional theory (DFT) calculations and configuration-interaction shell-model (CISM) calculations are compared with the experimental results. All theoretical approaches face challenges to reproduce the trend of nuclear ground-state properties in the silver isotopic chain across the $N =$50 neutron shell and toward the proton drip-line.

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arXiv2024

High-precision measurements of the atomic mass and electron-capture decay $Q$ value of $^{95}$Tc

A direct measurement of the ground-state-to-ground-state electron-capture decay $Q$ value of $^{95}$Tc has been performed utilizing the double Penning trap mass spectrometer JYFLTRAP. The $Q$ value was determined to be 1695.92(13) keV by taking advantage of the high resolving power of the phase-imaging ion-cyclotron-resonance technique to resolve the low-lying isomeric state of $^{95}$Tc (excitation energy of 38.910(40) keV) from the ground state. The mass excess of $^{95}$Tc was measured to be $-$86015.95(18) keV/c$^2$, exhibiting a precision of about 28 times higher and in agreement with the value from the newest Atomic Mass Evaluation (AME2020). Combined with the nuclear energy-level data for the decay-daughter $^{95}$Mo, two potential ultra-low $Q$-value transitions are identified for future long-term neutrino-mass determination experiments. The atomic self-consistent many-electron Dirac--Hartree--Fock--Slater method and the nuclear shell model have been used to predict the partial half-lives and energy-release distributions for the two transitions. The dominant correction terms related to those processes are considered, including the exchange and overlap corrections, and the shake-up and shake-off effects. The normalized distribution of the released energy in the electron-capture decay of $^{95}$Tc to excited states of $^{95}$Mo is compared to that of $^{163}$Ho currently being used for electron-neutrino-mass determination.

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arXiv2022

Studying Gamow-Teller transitions and the assignment of isomeric and ground states at $N=50$

Direct mass measurements of neutron-deficient nuclides around the $N=50$ shell closure below $^{100}$Sn were performed at the FRS Ion Catcher (FRS-IC) at GSI, Germany. The nuclei were produced by projectile fragmentation of $^{124}$Xe, separated in the fragment separator FRS and delivered to the FRS-IC. The masses of 14 ground states and two isomers were measured with relative mass uncertainties down to $1\times 10^{-7}$ using the multiple-reflection time-of-flight mass spectrometer of the FRS-IC, including the first direct mass measurements of $^{98}$Cd and $^{97}$Rh. A new $Q_\mathrm{EC} = 5437\pm67$ keV was obtained for $^{98}$Cd, resulting in a summed Gamow-Teller (GT) strength for the five observed transitions ($0^+\longrightarrow1^+$) as $B(\text{GT})=2.94^{+0.32}_{-0.28}$. Investigation of this result in state-of-the-art shell model approaches sheds light into a better understanding of the GT transitions in even-even isotones at $N=50$. The excitation energy of the long-lived isomeric state in $^{94}$Rh was determined for the first time to be $293\pm 21$ keV. This, together with the shell model calculations, allows the level ordering in $^{94}$Rh to be understood.

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arXiv2018

FRIB and the GW170817 Kilonova

In July 2018 an FRIB Theory Alliance program was held on the implications of GW170817 and its associated kilonova for r-process nucleosynthesis. Topics of discussion included the astrophysical and nuclear physics uncertainties in the interpretation of the GW170817 kilonova, what we can learn about the astrophysical site or sites of the r process from this event, and the advances in nuclear experiment and theory most crucial to pursue in light of the new data. Here we compile a selection of scientific contributions to the workshop, broadly representative of progress in r-process studies since the GW170817 event.

astro-ph.HE↗

arXiv2017

Towards an Experimental Determination of the Transition Strength Between the Ground States of $^{20}$F and $^{20}$Ne

Electron capture on $^{20}$Ne is thought to play a crucial role in the final evolution of electron-degenerate ONe stellar cores. Recent calculations suggest that the capture process is dominated by the second-forbidden transition between the ground states of $^{20}$Ne and $^{20}$F, making an experimental determination of this transition strength highly desirable. To accomplish this task we are refurbishing an intermediate-image magnetic spectrometer capable of focusing 7 MeV electrons, and designing a scintillator detector surrounded by an active cosmic-ray veto shield, which will serve as an energy-dispersive device at the focal plane.

physics.ins-det↗