The first low-energy Coulomb-excitation measurement of the radioactive, semi-magic, two proton -hole nucleus 206Hg, was performed at CERN's recently-commissioned HIE-ISOLDE facility. Two gamma rays depopulating low-lying states in 206Hg were observed. From the data, a reduced transition strength B(E2; 2+1 -> 0+1 ) = 4.4(6) W.u. was determined, the first such value for an N = 126 nucleus south of 208Pb, which is found to be slightly lower than that predicted by shell-model calculations. In addition, a collective octupole state was identified at an excitation energy of 2705 keV, for which a reduced B(E3) transition probability of 30+10 -13 W.u. was extracted. These results are crucial for understanding both quadrupole and octupole collectivity in the vicinity of the heaviest doubly-magic nucleus 208Pb, and for benchmarking a number of theoretical approaches in this key region. This is of particular importance given the paucity of data on transition strengths in this region, which could be used, in principle, to test calculations relevant to the astrophysical r-process.(c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3.

Ever-lasting interest in the structure of 100 Sn and neighbouring nuclei is still well justified by the fact that it is the heaviest doubly-magic nucleus with N=Z. State-of-the-art experimental techniques involving stable and radioactive beam facilities have enabled access to these exotic nuclei. In particular, the analysis of experimental data obtained in two DESPEC experiments at GSI Darmstadt extends the information on the shell structure and its evolution towards N = Z = 50, and allows the study of seniority conservation and proton-neutron interaction in the g9/2 orbit. Several theoretical approaches for shell-model investigations are discussed and their predictive power assessed. The calculated systematics of the reduced transition probabilities for high- to medium-spin states in N∼Z isotopes with active g9/2 orbit is presented for the first time.

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.

The first low-energy Coulomb-excitation measurement of the radioactive, semi-magic, two proton-hole nucleus 206Hg, was performed at CERN's recently-commissioned HIE-ISOLDE facility. Two γ rays depopulating low-lying states in 206Hg were observed. From the data, a reduced transition strength B(E2;21+→01+)=4.4(6) W.u. was determined, the first such value for an N=126 nucleus south of 208Pb, which is found to be slightly lower than that predicted by shell-model calculations. In addition, a collective octupole state was identified at an excitation energy of 2705 keV, for which a reduced B(E3) transition probability of 30−13+10 W.u. was extracted. These results are crucial for understanding both quadrupole and octupole collectivity in the vicinity of the heaviest doubly-magic nucleus 208Pb, and for benchmarking a number of theoretical approaches in this key region. This is of particular importance given the paucity of data on transition strengths in this region, which could be used, in principle, to test calculations relevant to the astrophysical r-process.

A new beta-decaying state in Bi-214 has been identified at the ISOLDE Decay Station at the CERN-ISOLDE facility. A preferred I-pi = (8(-)) assignment was suggested for this state based on the beta-decay feeding pattern to levels in Po-214 and shell-model calculations. The half-life of the I-pi = (8) state was deduced to be T-1/2 = 9.39(10) min. The deexcitation of the levels populated in Po-214 by the beta decay of this state was investigated via gamma-gamma coincidences and a number of new levels and transitions was identified. Shell-model calculations for excited states in Bi-214 and Po-214 were performed using two different effective interactions: the H208 and the modified Kuo-Herling particle interaction. Both calculations agree on the interpretation of the new beta-decaying state as an I-pi = 8 - isomer and allow for tentative assignment of shell-model states to several high-spin states in Po-214.

Summary. — This paper reports preliminary results of the DESPEC campaign at GSI, focused on the study of neutron-deficient nuclei approaching 100 Sn. The results presented show the isomeric decays of excited states with I π = 14 + and 8 + in 96 Pd and 94 Pd, respectively. The detailed characterisation of the DESPEC set-up and analysis methodologies, proven in this experimental run, are crucial for the future campaigns.

Received 23 November 2017DOI:https://doi.org/10.1103/PhysRevC.97.019901©2018 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasElectromagnetic transitionsIsomer decaysLifetimes & widthsNuclear structure & decaysProperties59 ≤ A ≤ 8990 ≤ A ≤ 149TechniquesShell modelNuclear Physics

In a high-energy fragmentation experiment at GSI an I=π(6+) isomer and its γ-decay are identified in 102Sn, the two-neutron neighbour of the doubly-magic 100Sn. Its half-life is measured to be T=1/2367(11) ns. The possible existence of further isomers is discussed in the framework of large-scale shell model (LSSM) calculations including up to five particle-hole excitations of the 100Sn core. From the precise B(E2; 6+→4+) strength and the recently remeasured value for B(E2; 8+→6+) in the two-proton hole neighbour 98Cd effective E2 polarization charges for protons and neutrons were inferred including LSSM corrections within the full N=4 0ħω space. The results are discussed in comparison to predicted and empirically determined effective operators.

Excited states of 129In populated following the beta decay of Cd-129 were experimentally studied with the GRIFFIN spectrometer at the ISAC facility of TRIUMF, Canada. A 480-MeV proton beam was impinged on a uranium carbide target and Cd-129 was extracted using the Ion Guide Laser Ion Source (IG-LIS). beta and. rays following the decay of 129Cd were detected with the GRIFFIN spectrometer comprising the plastic scintillator SCEPTAR and 16 high-purity germanium (HPGe) clover-type detectors. From the beta-gamma-gamma coincidence analysis, 32 new transitions and seven new excited states were established, expanding the previously known level scheme of In-129. The log ft values deduced from the beta-feeding intensities suggest that some of the high-lying states were populated by the nu 0g7(/2) -> pi 0g(9/2) allowed Gamow-Teller (GT) transition, which indicates that the allowed GT transition is more dominant in the Cd-129 decay than previously reported. Observation of fragmented Gamow-Teller strengths is consistent with theoretical calculations.

We report on new γ-ray spectroscopy results from β decays of In99 and Sn101. 30 new γ rays were observed following the β decay of In99, and inconsistencies in the literature with respect to the γ rays following the β decay of Sn101 were addressed with two confirmed cases and two new transitions. The experimental γ-ray energies, intensities, and coincidence relationships are discussed with shell model calculations, where theoretical β-decay branching ratios from the parent nuclei and γ-ray cascades of excited states from the daughter nuclei were combined to generate hypothetical βγ spectra and βγγ coincidence matrices. The most intense β-delayed γ-ray branches in both Cd99 and In101 were well reproduced with this approach, and several γ rays were assigned to new excited states based on their good agreement with shell model predictions.

The beta decay of Hg-207 into the single-proton-hole nucleus Tl-207 has been studied through gamma-ray spectroscopy at the ISOLDE Decay Station (IDS) with the aim of identifying states resulting from coupling of the pi s(1/2)(-1), pi d(3/2)(-1) and pi h(11/2)(-1) shell model orbitals to the collective octupole vibration. Twenty-two states were observed lying between 2.6 and 4.0 MeV, eleven of which were observed for the first time, and 78 new transitions were placed. Two octupole states (s(3/2)-coupled) are identified and three more states (d(3/2)-coupled) are tentatively assigned using spin-parity inferences, while further h(11/2)-coupled states may also have been observed for the first time. Comparisons are made with state-of-the-art large-scale shell model calculations and previous observations made in this region, and systematic underestimation of the energy of the octupole vibrational states is noted. We suggest that in order to resolve the difference in predicted energies for collective and noncollective t = 1 states (t is the number of nucleons breaking the Pb-208 core), the effect of t = 2 mixing may be reduced for octupole-coupled states. The inclusion of mixing with t = 0, 2, 3 excitations is necessary to replicate all t = 1 state energies accurately.

We report on new gamma-ray spectroscopy results from beta decays of In-99 and Sn-101. 30 new gamma rays were observed following the beta decay of In-99, and inconsistencies in the literature with respect to the gamma rays following the beta decay of Sn-101 were addressed with two confirmed cases and two new transitions. The experimental gamma-ray energies, intensities, and coincidence relationships are discussed with shell model calculations, where theoretical beta-decay branching ratios from the parent nuclei and gamma-ray cascades of excited states from the daughter nuclei were combined to generate hypothetical beta gamma spectra and beta gamma gamma coincidence matrices. The most intense beta-delayed gamma-ray branches in both Cd-99 and In-101 were well reproduced with this approach, and several gamma rays were assigned to new excited states based on their good agreement with shell model predictions.

The β decay of ^{208}Hg into the one-proton hole, one neutron-particle _{81}^{208}Tl_{127} nucleus was investigated at CERN-ISOLDE. Shell-model calculations describe well the level scheme deduced, validating the proton-neutron interactions used, with implications for the whole of the N>126, Z<82 quadrant of neutron-rich nuclei. While both negative and positive parity states with spin 0 and 1 are expected within the Q_{β} window, only three negative parity states are populated directly in the β decay. The data provide a unique test of the competition between allowed Gamow-Teller and Fermi, and first-forbidden β decays, essential for the understanding of the nucleosynthesis of heavy nuclei in the rapid neutron capture process. Furthermore, the observation of the parity changing 0^{+}→0^{-}β decay where the daughter state is core excited is unique, and can provide information on mesonic corrections of effective operators.

Long-lived isomeric states in 97Ag and 101−109In were investigated with the FRS Ion Catcher at GSI. In the isotope 97Ag, a long-lived (1/2−) isomeric state was discovered, and its excitation energy was determined to be 618(38) keV. This is simultaneously the first discovery of a nuclear isomeric state by multiple-reflection time-of-flight mass spectrometry. The measured excitation energies were compared to large-scale shell-model calculations, which indicated the importance of core excitation around 100Sn. Furthermore, advanced mean-field calculations for the 97Ag nucleus and relevant neighboring nuclei were performed, which have contributed to a better understanding of the repetitive appearance of certain isomeric structures in neighboring nuclei, and which have supported the discovery of the isomeric state in 97Ag in a global shell-evolution scheme.

The β decay of 208Hg into the one-proton hole, one neutron-particle 20881Tl127 nucleus was investigated at CERN-ISOLDE. Shell-model calculations describe well the level scheme deduced, validating the proton-neutron interactions used, with implications for the whole of the N>126, Z<82 quadrant of neutron-rich nuclei. While both negative and positive parity states with spin 0 and 1 are expected within the Qβ window, only three negative parity states are populated directly in the β decay. The data provide a unique test of the competition between allowed Gamow-Teller and Fermi, and first-forbidden β decays, essential for the understanding of the nucleosynthesis of heavy nuclei in the rapid neutron capture process. Furthermore, the observation of the parity changing 0+→0−β decay where the daughter state is core excited is unique, and can provide information on mesonic corrections of effective operators.Received 7 July 2020Revised 21 September 2020Accepted 7 October 2020DOI:https://doi.org/10.1103/PhysRevLett.125.192501Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasNuclear structure & decaysNuclear Physics

Data analysis of the Coulomb excitation experiment of the exotic 206Hg nucleus, recently performed at CERN’s HIE-ISOLDE facility, needs to account for the contribution to target excitation due to the strongly-present beam contaminant 130Xe. In this paper, the contamination subtraction procedure is presented.

We report on new $\ensuremath{\gamma}$-ray spectroscopy results from $\ensuremath{\beta}$ decays of $^{99}\mathrm{In}$ and $^{101}\mathrm{Sn}$. 30 new $\ensuremath{\gamma}$ rays were observed following the $\ensuremath{\beta}$ decay of $^{99}\mathrm{In}$, and inconsistencies in the literature with respect to the $\ensuremath{\gamma}$ rays following the $\ensuremath{\beta}$ decay of $^{101}\mathrm{Sn}$ were addressed with two confirmed cases and two new transitions. The experimental $\ensuremath{\gamma}$-ray energies, intensities, and coincidence relationships are discussed with shell model calculations, where theoretical $\ensuremath{\beta}$-decay branching ratios from the parent nuclei and $\ensuremath{\gamma}$-ray cascades of excited states from the daughter nuclei were combined to generate hypothetical $\ensuremath{\beta}\ensuremath{\gamma}$ spectra and $\ensuremath{\beta}\ensuremath{\gamma}\ensuremath{\gamma}$ coincidence matrices. The most intense $\ensuremath{\beta}$-delayed $\ensuremath{\gamma}$-ray branches in both $^{99}\mathrm{Cd}$ and $^{101}\mathrm{In}$ were well reproduced with this approach, and several $\ensuremath{\gamma}$ rays were assigned to new excited states based on their good agreement with shell model predictions.