Dr Laetitia Canete

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

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. peerReviewed

We report the first high-precision mass measurements of the neutron-rich nuclei Ni-74,Ni-75 and the clearly identified ground state of Cu-76, along with a more precise mass-excess value of Cu-78, 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. (C) 2022 The Authors. Published by Elsevier B.V.

A precise determination of the ground state 111In (9/2+) electron capture to ground state of 111Cd (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 111Cd was used to determine whether the four states are energetically allowed for a potential ultra-low Q-value β decay or electron-capture decay. Our results confirm that the excited states of 866.60(6) keV with spin-parity (Jπ) of 3/2+ and 864.8(3) keV with Jπ=3/2+ are ruled out due to their deduced electron-capture Q value being smaller than 0 keV at the level of around 20σ and 50σ, respectively. Electron-capture decays to the excited states at 853.94(7) keV (Jπ=7/2+) and 855.6(10) keV (Jπ=3/2+), are energetically allowed with Q values of 3.69(19) keV and 2.0(10) keV, respectively. The allowed decay transition 111In (9/2+) → 111Cd (7/2+), with a Q value of 3.69(19) keV, is a potential new candidate for neutrino-mass measurements by future EC experiments featuring new powerful detection technologies. The results show that the indium level 2p1/2 for this decay branch leads to a significant increase in the number of EC events in the energy region sensitive to the electron neutrino mass.

Neutron-rich Pd-119 nuclei were produced in fission of natural uranium, induced by 25-MeV protons. Fission fragments swiftly extracted with the Ion Guide Isotope Separation On-Line method were mass separated using a dipole magnet and a Penning trap, providing mono-isotopic samples of Pd-119. Their beta(-) decay was measured with gamma gamma- and beta gamma-spectroscopy methods using low-energy germanium detectors and a thin plastic scintillator. Two distinct nuclear-level structures were observed in Ag-119, based on the 1/2(-) and 7/2(+) isomers reported previously. The beta(-)decay work was complemented by a prompt-gamma study of levels in Ag-119 populated in spontaneous fission of (252)cf, performed using the Gammasphere array of germanium detectors. Contrary to previous suggestions, our data show that the 1/2(-) isomer is located below the 7/2(+) isomer and is proposed as a new ground state of Ag-119 with the 7/2(+) isomer excitation energy determined to be 33.4 keV. Our data indicate that there are two beta unstable isomers in Pd-119, a proposed ground state of Pd-119 with tentative spin 1/2(-) or 3/2(+) and a half-life of 0.88 s and the other one about 350 keV above, having spin (11/2(-)) and a half-life of 0.85 s. The higher-energy isomer probably decays to the 1/2(-) or 3/2(+) ground state via a gamma cascade comprising 18.7-219.8-X-keV transitions. The unobserved isomeric transition with energy X approximate to 100 keV probably has an E3 multipolarity. Its hindrance factor is significantly lower than for analogous E3 isomeric transitions in lighter Pd isotopes, suggesting an oblate deformation of levels in Pd-119. Oblate configurations in Ag-119 are discussed also.

The impact of nuclear deformation can been seen in the systematics of nuclear charge radii, with radii generally expanding with increasing deformation. In this Letter, we present a detailed analysis of the precise relationship between nuclear quadrupole deformation and the nuclear size. Our approach combines the first measurements of the changes in the mean-square charge radii of well-deformed palladium isotopes between A 1/4 98 and A 1/4 118 with nuclear density functional calculations using Fayans functionals, specifically Fy(std) and Fyo Delta r, HFB thorn , and the UNEDF2 functional. The changes in mean-square charge radii are extracted from collinear laser spectroscopy measurements on the 4d95s 3D3 -> 4d95p 3P2 atomic transition. The analysis of the Fayans functional calculations reveals a clear link between a good reproduction of the charge radii for the neutron-rich Pd isotopes and the overestimated odd-even staggering: Both aspects can be attributed to the strength of the pairing correlations in the particular functional which we employ.

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, Pm-161, Sm-163, Eu-164,Eu-165, Gd-167, and Tb-165,Tb-167,Tb-168, 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 approximate to 165.

Low-spin, excited states of the Br-89 nucleus, populated in beta(-)decay of Se-89 have been studied for the first time. The Se-89 nuclei were produced in proton-induced fission of natural thorium using the IGISOL facility and separated using a dipole magnet and the coupled JYFLTRAP Penning trap. Gamma radiation following the beta(-) decay of Se-89 was measured with an array of high-resolution germanium detectors. Levels scheme of Br-89 was extended by 12 new levels and 31 new gamma transitions. Spin-parity (3/2(+)) has been proposed for the ground state of the Se-89 mother nucleus, replacing the (5/2(+)) assignment reported in data bases. The observed Gamow-Teller beta(-) transition to the 1754.5-keV level indicates a pi g(9/2)-based configuration. The level scheme of Br-89 has been compared to large scale shell-model calculations. Excitations based on pi p(3/2) and pi f(5/2) single-particle levels as well as their anomalous coupling are proposed to explain the low-energy excitation scheme of Br-89.

Understanding the evolution of the nuclear charge radius is one of the long-standing challenges for nuclear theory. Recently, density functional theory calculations utilizing Fayans functionals have successfully reproduced the charge radii of a variety of exotic isotopes. However, difficulties in the isotope production have hindered testing these models in the immediate region of the nuclear chart below the heaviest self-conjugate doubly-magic nucleus Sn-100, where the near-equal number of protons (Z) and neutrons (N) lead to enhanced neutron-proton pairing. Here, we present an optical excursion into this region by crossing the N = 50 magic neutron number in the silver isotopic chain with the measurement of the charge radius of Ag-96 (N = 49). The results provide a challenge for nuclear theory: calculations are unable to reproduce the pronounced discontinuity in the charge radii as one moves below N = 50. The technical advancements in this work open the N = Z region below Sn-100 for further optical studies, which will lead to more comprehensive input for nuclear theory development. Laser spectroscopic measurements of isotopes near the doubly-magic 100-Sn are challenging due to difficulties in their production. Here the authors measure the ground state charge radius of the proton-rich 96-Ag isotope and find a discontinuity in the nuclear size when crossing the neutron number N equal to 50.

Accurate mass measurements of neutron-rich iron and cobalt isotopes Fe-67 and Co-69,Co-70 have been realized with the JYFLTRAP double Penning-trap mass spectrometer. With novel ion-manipulation techniques, the masses of the Co-69,Co-70 ground states and the 1/2(-) isomer in Co-69 have been extracted for the first time. The measurements remove ambiguities in the previous mass values and yield a smoother trend on the mass surface, extending it beyond N = 40. The moderate N = 40 subshell gap has been found to weaken below Ni-68, a region known for shape coexistence and increased collectivity. The excitation energy for the 1/2(-) intruder state in Co-69 has been determined for the first time and is compared to large-scale shell-model calculations. The new mass values also reduce significantly mass-related uncertainties for the astrophysical rapid neutron-capture process calculations.

The ground-state-to-ground-state beta-decay Q value of Cs-135(7/ 2(+)) -> Ba-135(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 Penningtrap setup and yielded a mass difference of 268.66(30) keV between Cs-135(7/2(+)) and Ba-135(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 beta(-)-decay transition Cs-135(7/2(+)) -> Ba-135(11/2(-)) is a candidate for antineutrino mass measurements with an ultralow Q value of 0.44(31) keV. This Q value is almost an order of magnitude smaller than those of nuclides presently used in running or planned direct (anti)neutrino mass experiment.

The 25 Al(p, γ) reaction has long been highlighted as a possible means to bypass the production of 26 Al cosmic γ rays in classical nova explosions. However, uncertainties in the properties of key resonant states in 26 Si have hindered our ability to accurately model the influence of this reaction in such environments. We report on a detailed γ-ray spectroscopy study of 26 Si and present evidence for the existence of a new, likely ℓ = 1, resonance in the 25 Al + p system at Er = 153.9(15) keV. This state is now expected to provide the dominant contribution to the 25 Al(p, γ) stellar reaction rate over the temperature range, T ∼ 0.1 − 0.2 GK. Despite a significant increase in the rate at low temperatures, we find that the final ejected abundance of 26 Al from classical novae remains largely unaffected even if the reaction rate is artificially increased by a factor of 10. Based on new, Galactic chemical evolution calculations, we estimate that the maximum contribution of novae to the observed Galactic abundance of 26 Al is ∼0.2 M⊙. Finally, we briefly highlight the important role that Super-AGB stars may play in the production of 26 Al.

Isomeric states in 128In and 130In 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 128In and 130In 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 isomer in 128Sn has been discovered in 128In 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 130In, the lowest-lying (10⁻) isomeric state at 58.6(82) keV was resolved for the first time using the phase-imaging ion cyclotron resonance technique. The energy difference between the 10⁻ and 1⁻ states in 130In, stemming from parallel/antiparallel coupling of (π0g-19/2) ⊗ (v0h-111/2), has been found to be around 200 keV lower than predicted by the shell model. Precise information on the energies of the excited states determined in this work is crucial for producing new improved effective interactions for the nuclear shell model description of nuclei near 132Sn.

Two long-standing puzzles in the decay of ¹⁸⁵Bi, the heaviest known proton-emitting nucleus are revisited. These are the nonobservation of the 9/2(-) state, which is the ground state of all heavier odd-A Bi isotopes, and the hindered nature of proton and alpha decays of its presumed 60-mu s 1/2(+) ground state. The ¹⁸⁵Bi nucleus has now been studied with the ⁹⁵Mo(⁹³Nb, 3n) reaction in complementary experiments using the Fragment Mass Analyzer and Argonne Gas-Filled Analyzer at Argonne National Laboratory's ATLAS facility. The experiments have established the existence of two states in ¹⁸⁵Bi; the short-lived T-1/2 = 2.8(-1.0)(+2.3) mu s, proton- and alpha-decaying ground state, and a 58(2)-mu s gamma-decaying isomer, the half-life of which was previously attributed to the ground state. The reassignment of the ground-state lifetime results in a proton-decay spectroscopic factor close to unity and represents the only known example of a ground-state proton decay to a daughter nucleus (¹⁸⁴Pb) with a major shell closure. The data also demonstrate that the ordering of low- and high-spin states in ¹⁸⁵Bi is reversed relative to the heavier odd-A Bi isotopes, with the intruder-based 1/2(+) configuration becoming the ground, similar to the lightest At nuclides.

The astrophysical 25Al(p,γ) 26Si reaction represents one of the key remaining uncertainties in accurately modeling the abundance of radiogenic 26Al ejected from classical novae. Specifically, the strengths of key proton-unbound resonances in 26Si, that govern the rate of the 25Al(p,γ) reaction under explosive astrophysical conditions, remain unsettled. Here, we present a detailed spectroscopy study of the 26Si mirror nucleus 26Mg. We have measured the lifetime of the 3+, 6.125-MeV state in 26Mg to be 19(3) fs and provide compelling evidence for the existence of a 1– state in the T = 1, A = 26 system, indicating a previously unaccounted for ℓ = 1 resonance in the 25Al(p,γ) reaction. Using the presently measured lifetime, together with the assumption that the likely 1– state corresponds to a resonance in the 25Al + p system at 435.7(53) keV, we find considerable differences in the 25Al(p,γ) reaction rate compared to previous works. Furthermore, based on current nova models, we estimate that classical novae may be responsible for up to ≈ 15% of the observed galactic abundance of 26Al.