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19 pags., 14 figs., 3 tabs., A γ-ray spectroscopic study of Po212 was performed at the Grand Accélérateur National d'Ions Lourds, using the inverse kinematics α-transfer reaction C12(Pb208,Po212)Be8 and the AGATA spectrometer. A careful analysis based on γγ coincidence relations allowed us to establish 14 new excited states in the energy range between 1.9 and 3.3 MeV. None of these states, however, can be considered as candidates for the levels with spins and parities of 1- and 2- and excitation energies below 2.1 MeV, which have been predicted by recent α-cluster model calculations. A systematic comparison of the experimentally established excitation scheme of Po212 with shell-model calculations was performed. This comparison suggests that the six states with excitation energies (spins and parities) of 1744 (4-), 1751 (8-), 1787 (6-), 1946 (4-), 1986 (8-), and 2016 (6-) keV, which previously were interpreted as α-cluster states, may in fact be of positive parity and belong to low-lying shell-model multiplets. This reinterpretation of the structure of Po212 is supported by experimental information with respect to the linear polarization of γ rays, which suggests a magnetic character of the 432-keV γ ray decaying from the state at an excitation energy of 1787 keV to the 61+ yrast state, and exclusive reaction cross sections., This project has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No. 654002 and FEDER funds. We furthermore acknowledge support from the Spanish Ministerio de Ciencia, Inovación y Universidades under contracts FPA2014-57196-C5, FPA2017-84756-C4, and SEV-2014-0398, the Generalitat Valenciana under Grant No. PROMETEO/2019/005, the Swedish Research Council (Vetenskapsrådet, VR 2016-3969), and the German BMBF under Contracts No. 05P18PKFN9 and No. 05P19PKFNA.

Background: Neutron-rich nuclei with mass number between 100 and 110 attract much attention, since several kinds of shapes, such as spherical, prolate, oblate, and triaxial shapes, are predicted. In particular, for neutron-rich Mo isotopes, different models predict different magnitudes and rigidity of triaxial deformation. Previous interpretations of experimental results based solely on low-lying 2+2 states are insufficient to distinguish between the rigid triaxial shape, γ vibration, or γ -soft rotor. Purpose: The shape evolution of 106Mo, 108Mo, and 110Mo is investigated through their 2+1-state lifetimes, decay-branching ratios of the 2+2 state, and energies of the low-lying collective excited states with Kπ = 0+, 2+, and 4+. Method: β -delayed γ -ray spectroscopy was employed for neutron-rich Nb and Zr isotopes produced at the RIKEN RI Beam Factory to populate excited states in 106Mo , 108Mo , and 110Mo . The EUroball-RIKEN Cluster Array was used for high-resolution γ -ray detection and lifetimes of the 2+1 states were determined using the UK fast-timing array of LaBr3(Ce) detectors. Results: New γ -ray transitions and levels are reported, including newly assigned 0+2 states in 108,110Mo . Quadrupole deformations were obtained for 106,108,110Mo from their 2+1 energies and lifetimes. The β -delayed neutron-emission probabilities of 108 Nb and 110 Nb were determined by examining the γ rays of their respective daughter decays. Conclusions: The even-odd energy staggering in the 2+2 band was compared with typical patterns of the γ -vibrational band, rigid triaxial rotor, and γ -soft rotor. The very small even-odd staggering of 106 Mo, 108Mo, and 110Mo favors a γ -vibrational band assignment. The kinematic moment of inertia for the 2+2 band showed a trend similar to the ground-state band, which is as expected for the γ -vibrational band. Beyond-mean-field calculations employing the constrained Hartree-Fock-Bogoliubov and local quasiparticle-random-phase approximation method using the SLy 5 + T interaction reproduced the ground and 2+2 bands in 106Mo and 108Mo . The collective wave functions are consistent with the interpretation of the 2+2 band as the γ -vibrational band of the prolate shape. However, the staggering pattern observed in 110Mo differs from the one suggested in the calculations which predict a γ -soft rotor. There was no experimental indication of the oblate shape or the γ -soft rotor predicted in these Mo isotopes.

Excited states of the neutron-rich nucleus 148Ce have been populated by neutron-induced fission of 235U and 241Pu samples. Their electromagnetic decays were studied by means of γ-ray coincidence spectroscopy with fast-timing capabilities. Lifetimes of the 2+1 and 4+1 states of 148Ce were obtained and their E2 decay rates deduced. The B4=2 = B(E2; 4+1 → 2+1)=B(E2; 2+1 → 0+1) ratio indicates that 148Ce is a transitional nucleus while the N = 88/90 shape phase transition evolves into a gradual change of nuclear deformation for proton numbers Z < 60.

Using a hybrid Gammasphere array coupled to 25 LaBr3(Ce) detectors, the lifetimes of the first three levels of the yrast band in ¹¹⁴Pd populated via ²⁵²Cf decay, have been measured. The measured lifetimes are τ₂+=103(10)ps, τ₄+=22(13)ps, and τ₆+≤10ps for the 2⁺₁, 4⁺₁, and 6⁺₁ levels, respectively. Palladium-114 was predicted to be the most deformed isotope of its isotopic chain, and spectroscopic studies have suggested it might also be a candidate nucleus for low-spin stable triaxiality. From the lifetimes measured in this work, reduced transition probabilities B(E2;J→J−2) are calculated and compared with interacting boson model, projected shell model, and collective model calculations from the literature. The experimental ratio RB(E₂)=B(E2;4⁺₁→2⁺₁)/B(E2;2⁺₁→0⁺₁)=0.80(42) is measured for the first time in ¹¹⁴Pd and compared with the known values RB(E₂) in the palladium isotopic chain: the systematics suggest that, for N=68, a transition from γ-unstable to a more rigid γ-deformed nuclear shape occurs.

The transitional nuclei ¹³⁴Ba and ¹³³Ba are investigated after multinucleon transfer employing the high-resolution Advanced GAmma Tracking Array coupled to the magnetic spectrometer PRISMA at the Laboratori Nazionali di Legnaro, Italy, and after fusion-evaporation reaction at the FN tandem accelerator of the University of Cologne, Germany. The Jπ=19/2⁺ state at 1942 keV in ¹³³Ba is identified as an isomer with a half-life of 66.6(20)ns corresponding to a B(E1) value of 7.7(4)×10⁻⁶e²fm² for the Jπ=19/2⁺ to Jπ=19/2⁻ transition. The level scheme of ¹³⁴Ba above the Jπ=10⁺ isomer is extended to approximately 6 MeV. A pronounced backbending is observed at ℏω=0.38 MeV along the positive-parity yrast band. The results are compared to the high-spin systematics of the Z=56 isotopes. Large-scale shell-model calculations employing the GCN50:82, SN100PN, SNV, PQM130, Realistic SM, and EPQQM interactions reproduce the experimental findings and elucidate the structure of the high-spin states. The shell-model calculations employing the GCN50:82 and PQM130 interactions reproduce alignment properties and provide detailed insight into the microscopic origin of this phenomenon in transitional ¹³⁴Ba.

6 pags., 4 figs., 1 tab., We report on the observation of a microsecond isomeric state in the single-proton-hole, three-neutron-particle nucleus In-134. The nuclei of interest were produced by in-flight fission of a U-238 beam at the Radioactive Isotope Beam Factory at RIKEN. The isomer depopulates through a gamma ray of energy 56.7(1) keV and with a half-life of T-1/2 = 3.5(4) mu s. Based on the comparison with shell-model calculations, we interpret the isomer as the I-pi = 5(-) member of the pi 0g(9/2)(-1) circle times nu 1f(7/2)(3) multiplet, decaying to the I-pi = 7(-) ground state with a reduced-transition probability of B(E2; 5(-) -> 7(-)) = 0.53(6) W.u. Observation of this isomer, and lack of evidence in the current work for a I-pi = 5(-) isomer decay in In-132, provides a benchmark of the proton-neutron interaction in the region of the nuclear chart >southeast> of Sn-132, where experimental information on excited states is sparse., This experiment was performed at RI Beam Factory operated by RIKEN Nishina Center and CNS, University of Tokyo. This research was sponsored in part by the Office of Nuclear Physics, U.S. Department of Energy under Awards No. DE-FG02-96ER40983 (UTK) and No. DE-AC05- 00OR22725 (ORNL), and by the National Nuclear Security Administration under the Stewardship Science Academic Alliances program through DOE Award No. DE-NA0002132, by the National Science Foundation under Grants No. PHY1430152 (JINA Center for the Evolution of the Elements), No. PHY-1565546 (NSCL), and No. PHY1714153 (Central Michigan University), by the Polish National Science Center under Contract No. UMO-2015/18/E/ST2/00217, by JSPS KAKENHI (Grants No. 14F04808, No. 17H06090, No. 25247045, and No. 19340074), by the UK Science and Technology Facilities Council ST/P005314/1, by NKFIH (NN128072), by the Janos Bolyai research fellowship of the Hungarian Academy of Sciences, by the UNKP-18- 4-DE-449 New National Excellence Program of the Ministry of Human Capacities of Hungary, by Spanish Ministerio de Economia y Competitividad grants (FPA2017- 83946-C2-1-P, FPA2011-28770-C03-03, FPA2014-52823- C2-1-P, FPA2014-52823-C2-2-P, FPA2014-57196-C5-4-P, FPA2017-84756-C4-2-P, SEV-2014-0398, and IJCI-2014- 19172), by European Commission FP7/EURATOM Contract No. 605203, by the UK Nuclear Data Network funded by the UK Science and Technology Facilities Council Grant No. ST/N00244X/1, by the National Research Foundation (NRF) in South Korea (Grants No. 2016K1A3A7A09005575 and No. 2015H1A2A1030275), and by the Natural Sciences and Engineering Research Council of Canada (NSERC) via the Discovery Grants No. SAPIN-2014-00028 and No. RGPAS 462257-2014. TRIUMF receives federal funding via a contribution agreement with the National Research Council of Canada. N.P.L. receives funding from the UK Department of Business Energy and Industrial Strategy (BEIS) via the NMS program. Shell-model calculations are supported by the National Natural Science Foundation of China 11775316. L.H.K. acknowledges Vietnam Academy of Science and Technology for support under the Program of Development in the Field of Physics by 2020–Study of unstable nuclei beam induced nuclear reaction at RIKEN. V.H.P. would like to express his deep gratitude to the RIKEN institute for the support during the term of IPA program at RIKEN Nishina Center.

We report on the observation of a microsecond isomeric state in the single-proton-hole, three-neutron-particle nucleus ¹³⁴In. The nuclei of interest were produced by in-flight fission of a ²³⁸U beam at the Radioactive Isotope Beam Factory at RIKEN. The isomer depopulates through a γ ray of energy 56.7(1) keV and with a half-life of T1/2=3.5(4)μs. Based on the comparison with shell-model calculations, we interpret the isomer as the Iπ=5− member of the π0g−19/2⊗ν1f37/2 multiplet, decaying to the Iπ=7− ground state with a reduced-transition probability of B(E2;5−→7−)=0.53(6)W.u.Observation of this isomer, and lack of evidence in the current work for a Iπ=5− isomer decay in ¹³²In, provides a benchmark of the proton-neutron interaction in the region of the nuclear chart “southeast” of ¹³²Sn, where experimental information on excited states is sparse.

The neutron-rich isotopes 211;213Tl, beyond the N = 126 shell-closure, have been studied for the first time in isomer γ-ray decay, exploiting the fragmentation of a primary uranium beam at the FRS-RISING (FRagment Separator-Rare ISotopes INvestigation at GSI) setup at GSI. The observed isomeric states in 211;213Tl show a deviation from the seniority-like scheme of 209Tl. The possible interpretation of the data is discussed on the basis of energy-level systematics and shell-model calculations.

Yrast and near-yrast levels up to an I=17ℏ spin value and a 6-MeV excitation energy have been delineated in the “two-neutron” 210Pb nucleus following deep-inelastic reactions involving 208Pb targets and a number of heavy-ion beams at energies ∼25% above the Coulomb barrier. The level scheme was established on the basis of multifold prompt and delayed coincidence relationships measured with the Gammasphere array. In addition to the previously known states, many new levels were identified. For most of the strongly populated states, spin-parity assignments are proposed on the basis of angular distributions. The reinvestigation of the ν(g9/2)2, 8+ isomeric decay results in the firm identification of the low-energy E2 transitions involved in the 8+→6+→4+ cascade, and in a revised 6+ level half-life of 92(10) ns, nearly a factor of 2 longer than previously measured. Among the newly identified states figure spin I=4–10ℏ levels associated with the νg9/2i11/2 multiplet, as well as yrast states involving νg9/2j15/2, νi11/2j15/2, and ν(j15/2)2 neutron couplings. The highest-spin excitations are understood as 1p−1h core excitations and the yrast population is found to be fragmented to the extent that levels of spin higher than I=17ℏ could not be reached. Four E3 transitions are present in the 210Pb yrast decay; three of these involve the g9/2→j15/2 octupole component, as reflected in the 21(2) and >10 Weisskopf unit enhancements of the B(E3) rates of the first two. The fourth, 16+→13−E3 transition corresponds to the 3− core octupole excitation built on the νi11/2j15/2 state, in analogy to a similar E3 coupling to the νj15/2 level in 209Pb. Shell-model calculations performed for two-neutron states and 1p−1h 208Pb core excitations are in good agreement with the data. Evidence was found for the existence of a hitherto unknown high-spin β-decaying isomer in 210Tl. Shell-model calculations of the 210Tl levels suggest the possibility of a 11+ long-lived, β-decaying state, and the delayed yields observed in various reactions fit rather well with a 210Tl assignment.

Yrast and near-yrast levels up to spin values in excess of I=30 have been delineated in the doubly magic Pb208 nucleus following deep-inelastic reactions involving Pb208 targets and, mostly, 430-MeV Ca48 and 1440-MeV Pb208 beams. The level scheme was established up to an excitation energy of 16.4 MeV, based on multifold γ-ray coincidence relationships measured with the Gammasphere array. Below the well-known, 0.5-μs 10+ isomer, ten new transitions were added to earlier work. The delineation of the higher parts of the level sequence benefited from analyses involving a number of prompt- and delayed-coincidence conditions. Three new isomeric states were established along the yrast line with Iπ=20- (10 342 keV), 23+ (11 361 keV), and 28- (13 675 keV), and respective half-lives of 22(3), 12.7(2), and 60(6) ns. Gamma transitions were also identified preceding in time the 28- isomer; however, only a few could be placed in the level scheme and no firm spin-parity quantum numbers could be proposed. In contrast, for most states below this 28- isomer, firm spin-parity values were assigned, based on total electron-conversion coefficients, deduced for low-energy (

The 54Fe nucleus was populated from a 56Fe beam impinging on a Be target with an energy of E/A=500MeV. The internal decay via γ-ray emission of the 10+ metastable state was observed. As the structure of this isomeric state has to involve at least four unpaired nucleons, it cannot be populated in a simple two-neutron removal reaction from the 56Fe ground state. The isomeric state was produced in the low-momentum (-energy) tail of the parallel momentum (energy) distribution of 54Fe, suggesting that it was populated via the decay of the Δ0 resonance into a proton. This process allows the population of four-nucleon states, such as the observed isomer. Therefore, it is concluded that the observation of this 10+ metastable state in 54Fe is a consequence of the quark structure of the nucleons.

WOS: 000326096300003 Lifetimes of the low-lying (11/2(-)) states in Co-63,Co-65 have been measured employing the recoil distance doppler shift method (RDDS) with the AGATA gamma-ray array and the PRISMA mass spectrometer. These nuclei were populated via a multinucleon transfer reaction by bombarding a U-238 target with a beam of Ni-64. The experimental B(E2) reduced transition probabilities for Co-63,Co-65 are well reproduced by large-scale shell-model calculations that predict a constant trend of the B(E2) values up to the N = 40 Co-67 isotope. German BMBF [06 DA 9040 I]; Spanish MINECO [AIC-D-2011-0746, FPA2011-29854]; Generalitat Valenciana (Spain) [PROMETEO/2010/101]; Polish MNiSW [DPN/N190/AGATA/2009]; Science and Technology Facilities Council [ST/I506010/1, ST/F004176/1, ST/I504932/1, ST/J000051/1] The authors want to thank the partial funding of this project by the German BMBF under Contract No. 06 DA 9040 I, the Spanish MINECO under Grants No. AIC-D-2011-0746 and No. FPA2011-29854, the Generalitat Valenciana (Spain) under Grant No. PROMETEO/2010/101, and the Polish MNiSW under Grant No. DPN/N190/AGATA/2009.

We present results from stopped beam rare isotope spectroscopic investigations at the GSI (RISING) experiment based on the detection of gamma-ray transitions following the beta decay of Pd-94. A comparison between the measured low-lying level scheme of Rh-94 and the prediction from shell-model calculations reveals the important roles of the g(7/2) and g(9/2) orbitals in explaining the structural features. The low values of the Gamow-Teller strengths B(GT) can be attributed to the influence of the neutron-proton interaction, which gives rise to an increased seniority mixing for the nuclear states, thereby leading to a fragmentation of the strength to several daughter levels. These results provide further strong indications that Pd-94 resides in the middle of a structural transition region in the Pd isotopes as the N = Z line is approached.

A beta-decaying high-spin isomer in Cd-96, with a half-life T-1/2 = 0.29(-0.10)(+0.11) s, has been established in a stopped beam rare isotope spectroscopic investigations at GSI (RISING) experiment. The nuclei were produced using the fragmentation of a primary beam of Xe-124 on a Be-9 target. From the half-life and the observed gamma decays in the daughter nucleus, Ag-96, we conclude that the beta-decaying state is the long predicted 16(+) "spin-gap'' isomer. Shell-model calculations, using the Gross-Frenkel interaction and the pi nu(p(1/2,)g(9/2)) model space, show that the isoscalar component of the neutron-proton interaction is essential to explain the origin of the isomer. Core excitations across the N = Z = 50 gaps and the Gamow-Teller strength, Bd(GT) distributions have been studied via large-scale shell-model calculations using the pi nu(g, d, s) model space to compare with the experimental B(GT) value obtained from the half-life of the isomer.