Ion Guide Isotope Separator On-Line Research Articles

Long-sought isomer turns out to be the ground state of 76Cu

Isomers close to the doubly magic nucleus 78Ni (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 76Cu has been debated for a long time. We have performed high-precision mass measurements of 76Cu with the JYFLTRAP double Penning trap mass spectrometer at the Ion Guide Isotope Separator On-Line facility and confirm the existence of such an isomeric state with an excitation energy Ex=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 76Cu. The result can potentially change the conclusions made in previous works related to the spin-parity and charge radius of the 76Cu ground state. Additionally, the new 76Cu(n,γ) reaction Q-value has an impact on the astrophysical rapid neutron-capture process.

First measurements with a new β-electron detector for spectral shape studies

The shape of the electron spectrum emitted in β decay carries a wealth of information about nuclear structure and fundamental physics. In spite of that, few dedicated measurements have been made of β-spectrum shapes. In this work we present a newly developed detector for β electrons based on a telescope concept. A thick plastic scintillator is employed in coincidence with a thin silicon detector. The first measurements employing this detector have been carried out with mono-energetic electrons from the high-energy resolution electron-beam spectrometer at Bordeaux. Here we report on the good reproduction of the experimental spectra of mono-energetic electrons using Monte Carlo simulations. This is a crucial step for future experiments, where a detailed Monte Carlo characterization of the detector is needed to determine the shape of the β-electron spectra by deconvolution of the measured spectra with the response function of the detector. A chamber to contain two telescope assemblies has been designed for future β-decay experiments at the Ion Guide Isotope Separator On-Line facility in Jyväskylä, aimed at improving our understanding of reactor antineutrino spectra.

Measurements of binding energies and electromagnetic moments of silver isotopes – A complementary benchmark of density functional theory

We report on a set of high-precision measurements of nuclear binding and excitation energies, as well as nuclear spins, magnetic dipole and electric quadrupole moments of neutron-rich silver isotopes, 113−123Ag. The measurements were performed using the JYFLTRAP mass spectrometer and the collinear laser spectroscopy beamline at the Ion Guide Isotope Separator On-Line (IGISOL) facility. For the first time, we can firmly establish the ordering of the long-lived Iπ=1/2−,7/2+ states in these isotopes, and pin down the inversion of these two levels at either A=121(N=74) or A=123(N=76). We compare these findings to calculations performed with density functional theory (DFT), from which we establish the crucial role that the spin-orbit strength and time-odd mean fields play in the simultaneous description of electromagnetic moments and nuclear binding.

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RAPTOR: A new collinear laser ionization spectroscopy and laser-radiofrequency double-resonance experiment at the IGISOL facility

RAPTOR, Resonance ionization spectroscopy And Purification Traps for Optimized spectRoscopy, is a new collinear resonance ionization spectroscopy device constructed at the Ion Guide Isotope Separator On-Line (IGISOL) facility at the University of Jyväskylä, Finland. By operating at beam energies of under 10keV, the footprint of the experiment is reduced compared to more traditional collinear laser spectroscopy beamlines. In addition, RAPTOR is coupled to the JYFLTRAP Penning trap mass spectrometer, opening a window to laser-assisted nuclear-state selective purification, serving not only the mass measurement program, but also supporting post-trap decay spectroscopy experiments. Finally, the low-energy ion beams used for RAPTOR will enable high-precision laser-radiofrequency double-resonance experiments, resulting in spectroscopy with linewidths below 1 MHz. In this contribution, the technical layout of RAPTOR and a selection of ion-beam optical simulations for the device are presented, along with a discussion of the current status of the commissioning experiments.

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 $^{110,112,114,116,118}\mathrm{Rh}$ and the very first mass measurement of $^{120}\mathrm{Rh}$. The isomeric states were separated and measured for the first time using the phase-imaging ion-cyclotron-resonance (PI-ICR) technique. For $^{112}\mathrm{Rh}$, 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.

Mass measurements towards doubly magic 78Ni: Hydrodynamics versus nuclear mass contribution in core-collapse supernovae

We report the first high-precision mass measurements of the neutron-rich nuclei 74,75Ni and the clearly identified ground state of 76Cu, along with a more precise mass-excess value of 78Cu, performed with the double Penning trap JYFLTRAP at the Ion Guide Isotope Separator On-Line (IGISOL) facility. These new results lead to a quantitative estimation of the quenching for the N=50 neutron shell gap. The impact of this shell quenching on core-collapse supernova dynamics is specifically tested using a dedicated statistical equilibrium approach that allows a variation of the mass model independent of the other microphysical inputs. We conclude that the impact of nuclear masses is strong when implemented using a fixed trajectory as in the previous studies, but the effect is substantially reduced when implemented self-consistently in the simulation.

Total absorption γ -ray spectroscopy of the β decays of Y96gs,m

The $\beta$ decays of the ground state (gs) and isomeric state (m) of $^{96}$Y have been studied with the total absorption $\gamma$-ray spectroscopy technique at the Ion Guide Isotope Separator On-Line facility. The separation of the 8$^{+}$ isomeric state from the 0$^{-}$ ground state was achieved thanks to the purification capabilities of the JYFLTRAP double Penning trap system. The $\beta$-intensity distributions of both decays have been independently determined. In the analyses the de-excitation of the 1581.6 keV level in $^{96}$Zr, in which conversion electron emission competes with pair production, has been carefully considered and found to have significant impact on the $\beta$-detector efficiency, influencing the $\beta$-intensity distribution obtained. Our results for $^{96\text{gs}}$Y (0$^+$) confirm the large ground state to ground state $\beta$-intensity probability, although a slightly larger value than reported in previous studies was obtained, amounting to $96.6_{-2.1}^{+0.3}\%$ of the total $\beta$ intensity. Given that the decay of $^{96\text{gs}}$Y is the second most important contributor to the reactor antineutrino spectrum between 5 and 7 MeV, the impact of the present results on reactor antineutrino summation calculations has been evaluated. In the decay of $^{96\text{m}}$Y (8$^{+}$), previously undetected $\beta$ intensity in transitions to states above 6 MeV has been observed. This shows the importance of total absorption $\gamma$-ray spectroscopy measurements of $\beta$ decays with highly fragmented de-excitation patterns. $^{96\text{m}}$Y (8$^{+}$) is a major contributor to reactor decay heat in uranium-plutonium and thorium-uranium fuels around 10 s after fission pulses, and the newly measured average $\beta$ and $\gamma$ energies differ significantly from the previous values in evaluated databases (...)

First trap-assisted decay spectroscopy of the ^{81}Ge ground state

The beta -delayed gamma spectroscopy of ^{81}As has been performed using a purified beam of ^{81}Ge (9/2^+) ground state at the Ion Guide Isotope Separator On-Line facility (IGISOL). The ^{81}Ge^+ ions were produced using proton-induced fission of ^{232}Th and selected with the double Penning trap JYFLTRAP for the post-trap decay spectroscopy measurements. The low-spin (1/2^+) isomeric-state ions ^{81m}hbox {Ge}^+ were not observed in the fission products. The intrinsic half-life of the ^{81}Ge ground state has been determined as T_{1/2}=6.4(2)~hbox {s}, which is significantly shorter than the literature value. A new level scheme of ^{81}As has been built and is compared to shell-model calculations.

Disentangling decaying isomers and searching for signatures of collective excitations in β decay

In this contribution we summarize the recent study of the β decay of neutron-rich nuclei with isomeric states close in energy to the ground states. The disentanglement of each pair of β-decaying states was achieved by applying different strategies and using the purification capabilities of the JYFLTRAP double Penning trap system at the Ion Guide Isotope Separator On-Line facility in Jyväskylä. The Total Absorption γ-ray Spectroscopy technique was employed to determine the β intensity probabilities populating the excited states in the daughter nuclei. Previously undetected β intensity was found and we have already evaluated the impact of part of these results on reactor summation calculations. The possibility to populate states associated with the Pygmy Dipole Resonance in the β decay of 96gsY has also been investigated thanks to the sensitivity of our technique to high-lying strength in the daughter nuclei.

High-precision mass measurement of 168Yb for verification of nonlinear isotope shift

The absolute mass value of 168Yb has been directly determined with the JYFLTRAP Penning trap mass spectrometer at the Ion Guide Isotope Separator On-Line (IGISOL) facility. A more precise value of the mass of 168Yb is needed to extract possible signatures of beyond standard model physics from high-precision isotope shift measurements of Yb atomic transition frequencies. The measured mass-excess value, ME(168Yb) = −61579.846(94) keV, is 13 times more precise and deviates from the Atomic Mass Evaluation 2016 value by 1.7σ. The impact on precision isotope shift studies of the stable Yb isotopes is discussed.

Exploring the mass surface near the rare-earth abundance peak via precision mass measurements at JYFLTRAP

The JYFLTRAP double Penning trap at the Ion Guide Isotope Separator On-Line facility has been used to measure the atomic masses of 13 neutron-rich rare-earth isotopes. Eight of the nuclides, $^{161}\mathrm{Pm}, ^{163}\mathrm{Sm}, ^{164,165}\mathrm{Eu}, ^{167}\mathrm{Gd}$, and $^{165,167,168}\mathrm{Tb}$, were measured for the first time. The systematics of the mass surface has been studied via one- and two-neutron separation energies as well as neutron pairing-gap and shell-gap energies. The proton-neutron pairing strength has also been investigated. The impact of the new mass values on the astrophysical rapid neutron capture process has been studied. The calculated abundance distribution results in a better agreement with the solar abundance pattern near the top of the rare-earth abundance peak at around $A\ensuremath{\approx}165$.

Recent experiments at the JYFLTRAP Penning trap

The JYFLTRAP double Penning trap mass spectrometer at the Ion Guide Isotope Separator On-Line (IGISOL) facility offers excellent possibilities for high-precision mass measurements of radioactive ions. Around 400 atomic masses, including around 50 isomeric states, have been measured since JYFLTRAP became operational. JYFLTRAP has also been used as a high-resolution mass separator for decay spectroscopy experiments as well as an ion counter for fission yield studies. In this contribution, an overview of recent activities at the JYFLTRAP Penning trap is given, with a focus on nuclei discussed in the PLATAN2019 meeting.

Total absorption γ -ray spectroscopy of niobium isomers

The $\beta$ intensity distributions of the decays of $^{100\text{gs},100\text{m}}$Nb and $^{102\text{gs},102\text{m}}$Nb have been determined using the Total Absorption $\gamma$-Ray Spectroscopy technique. The JYFLTRAP double Penning trap system was employed to disentangle the isomeric states involved, lying very close in energy, in a campaign of challenging measurements performed with the Decay Total Absorption $\gamma$-ray Spectrometer at the Ion Guide Isotope Separator On-Line facility in Jyv\"askyl\"a. The low-spin isomeric state of each niobium case was populated through the decay of the zirconium parent, that was treated as a contaminant. We have applied a method to extract this contamination, and additionally we have obtained $\beta$ intensity distributions for these zirconium decays. The $\beta$-strength distributions evaluated with these results were compared with calculations in quasiparticle random-phase approximation, suggesting a prolate configuration for the ground states of $^{100,102}$Zr. The footprint of the Pandemonium effect was found when comparing our results for the analyses of the niobium isotopes with previous decay data. The $\beta$-intensities of the decay of $^{102\text{m}}$Nb were obtained for the first time. A careful evaluation of the uncertainties was carried out, and the consistency of our results was validated taking advantage of the segmentation of our spectrometer. The final results were used as input in reactor summation calculations. A large impact on antineutrino spectrum calculations was already reported and here we detail the significant impact on decay heat calculations.

A new off-line ion source facility at IGISOL

An off-line ion source station has been commissioned at the IGISOL (Ion Guide Isotope Separator On-Line) facility. It offers the infrastructure needed to produce stable ion beams from three off-line ion sources in parallel with the radioactive ion beams produced from the IGISOL target chamber. This has resulted in improved feasibility for new experiments by offering reference ions for Penning-trap mass measurements, laser spectroscopy and atom trap experiments.

Large Impact of the Decay of Niobium Isomers on the Reactor ν[over ¯]_{e} Summation Calculations.

Even mass neutron-rich niobium isotopes are among the principal contributors to the reactor antineutrino energy spectrum. They are also among the most challenging to measure due to the refractory nature of niobium, and because they exhibit isomeric states lying very close in energy. The β-intensity distributions of ^{100gs,100m}Nb and ^{102gs,102m}Nb β decays have been determined using the total absorption γ-ray spectroscopy technique. The measurements were performed at the upgraded Ion Guide Isotope Separator On-Line facility at the University of Jyväskylä. Here, the double Penning trap system JYFLTRAP was employed to disentangle the β decay of the isomeric states. The new data obtained in this challenging measurement have a large impact in antineutrino summation calculations. For the first time the discrepancy between the summation model and the reactor antineutrino measurements in the region of the shape distortion has been reduced.

Simulations of the stopping efficiencies of fission ion guides

With the Ion Guide Isotope Separator On-Line (IGISOL) facility, located at the University of Jyvaskyla, products of nuclear reactions are separated by mass. The high resolving power of the JYFLTRAP Penning trap, with full separation of individual nuclides, capacitates the study of nuclides far from the line of stability. For the production of neutron-rich medium-heavy nuclides, fissioning of actinides is a feasible reaction. This can be achieved with protons from an in-house accelerator or, alternatively, with neutrons through the addition of a newly developed Be(p,xn)-converter. The hereby-obtained fission products are used in nuclear data measurements, for example fission yields, nuclear masses, Q-values and decay spectroscopy. Prior to separation, the ionized reaction products are stopped in a helium-filled gas cell, referred to as the ion-guide. In this work we present simulations of the stopping of fission products in an ion guide developed for neutron-induced fission. The production and extraction rates are evaluated and compared against experimental values.

Penning-trap-assisted study of excitations in Br88 populated in β decay of Se88

Excited levels of $^{88}\mathrm{Br}$ populated in the $\ensuremath{\beta}$ decay of $^{88}\mathrm{Se}$ have been studied by means of $\ensuremath{\beta}\ensuremath{\gamma}$ and $\ensuremath{\gamma}\ensuremath{\gamma}$ spectroscopy methods. Neutron-rich parent $^{88}\mathrm{Se}$ nuclei were produced with proton-induced fission of $^{238}\mathrm{U}$ using the Ion Guide Isotope Separator On-Line (IGISOL) method and separated from contaminants using a dipole magnet and the coupled JYFLTRAP Penning trap at the Accelerator Laboratory of the University of Jyv\askyl\a. The level scheme of $^{88}\mathrm{Br}$ has been constructed and $logft$ values of levels were determined. The ground-state spin of $^{88}\mathrm{Br}$ is now firmly determined to be ${1}^{\ensuremath{-}}$. Low-energy levels in $^{88}\mathrm{Br}$ were interpreted as members of the $\ensuremath{\pi}{p}_{3/2}{(\ensuremath{\nu}{d}_{5/2})}^{3}, \ensuremath{\pi}{p}_{3/2}^{\ensuremath{-}1}{(\ensuremath{\nu}{d}_{5/2})}^{3}, \ensuremath{\pi}{f}_{5/2}^{\ensuremath{-}1}{(\ensuremath{\nu}{d}_{5/2})}^{3}$, and $\ensuremath{\pi}{g}_{9/2}\ensuremath{\nu}{g}_{7/2}$ multiplets. The shell-model calculations performed in this work reproduce well the experimental results.

Mass of astrophysically relevantCl31and the breakdown of the isobaric multiplet mass equation

The mass of $^{31}$Cl has been measured with the JYFLTRAP double Penning trap mass spectrometer at the Ion-Guide Isotope Separator On-Line (IGISOL) facility. The determined mass-excess value, -7034.7(34) keV, is 15 times more precise than in the Atomic Mass Evaluation 2012. The quadratic form of the isobaric multiplet mass equation for the T=3/2 quartet at A=31 fails ($\chi^2_n$=11.6) and a non-zero cubic term, d=-3.5(11) keV, is obtained when the new mass value is adopted. $^{31}$Cl has been found to be less proton-bound with a proton separation energy of $S_p$=265(4) keV. Energies for the excited states in $^{31}$Cl and the photodisintegration rate on $^{31}$Cl have been determined with significantly improved precision using the new $S_p$ value. The improved photodisintegration rate helps to constrain astrophysical conditions where $^{30}$S can act as a waiting point in the rapid proton capture process in type I x-ray bursts.

Fission yield measurements at IGISOL

The fission product yields are an important characteristic of the fission process. In fundamental physics, knowledge of the yield distributions is needed to better understand the fission process. For nuclear energy applications good knowledge of neutroninduced fission-product yields is important for the safe and efficient operation of nuclear power plants. With the Ion Guide Isotope Separator On-Line (IGISOL) technique, products of nuclear reactions are stopped in a buffer gas and then extracted and separated by mass. Thanks to the high resolving power of the JYFLTRAP Penning trap, at University of Jyvaskyla, fission products can be isobarically separated, making it possible to measure relative independent fission yields. In some cases it is even possible to resolve isomeric states from the ground state, permitting measurements of isomeric yield ratios. So far the reactions U(p,f) and Th(p,f) have been studied using the IGISOL-JYFLTRAP facility. Recently, a neutron converter target has been developed utilizing the Be(p,xn) reaction. We here present the IGISOL-technique for fission yield measurements and some of the results from the measurements on proton induced fission. We also present the development of the neutron converter target, the characterization of the neutron field and the first tests with neutron-induced fission.