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The structure of Ge-80 has been investigated at the ISOLDE facility at CERN. A previous study reported for the first time a low-lying 0(2)(+) intruder state at 639 keV, based on the coincidence with a previously unobserved 1764-keV gamma ray, and suggested it as evidence for shape coexistence in Ge-80. We used the beta decay from the 3(-) 22.4-keV state in Ga-80 to enhance the population of low-spin states in Ge-80, including any excited 0(+) level, and gamma gamma coincidences to investigate it. We observed a 1764-keV gamma ray in coincidence with strong transitions in Ge-80, thus not feeding the proposed 639-keV 0(2)(+). No connecting transitions from previously known levels to the 639-keV and 2403-keV 2(3)(+) states could be established either. Shell-model calculations for Ge isotopes and N = 48 isotones were performed. They succeed to explain most of the experimental levels, but fail to reproduce the presence of a 0(2)(+) state below approximate to 1200 keV in Ge-80. Our experimental findings and shell-model calculations are difficult to reconcile with a very low-lying 0(2)(+) state in Ge-80.

The beta-decay of Zn-81 to the neutron magic N = 50 nucleus Ga-81, with only three valence protons with respect to Ni-78, was investigated. The study was performed at the ISOLDE facility at CERN by means of gamma spectroscopy. The 81Zn half-life was determined to be T-1/2 = 290(4) ms while the beta-delayed neutron emission probability was measured as P-n = 23(4)%. The analysis of the beta-gated gamma-ray singles and gamma-gamma coincidences from the decay of Zn-81 provides 47 new levels and 70 new transitions in Ga-81. The beta(-)n decay of Zn-81 was observed and a new decay scheme into the odd-odd Ga-80 nucleus was established. The half-lives of the first and second excited states of Ga-81 were measured via the fast-timing method using LaBr3(Ce) detectors. The level scheme and transition rates are compared to large-scale shell-model calculations. The low-lying structure of (81)Gais interpreted in terms of the coupling of the three valence protons outside the doubly magic Ni-78 core.

©2019 American Physical Society. This work was partially supported by the Spanish MINECO through Projects No. FPA2014-57196 and No. FPA2015-65035-P and Centro de Excelencia Severo Ochoa Programme (Project No. SEV-2016-0597). Support by Grupo de Física Nuclear (GFN-UCM) and by the European Union Seventh Framework through ENSAR (Contract No. 262010) is also acknowledged. B.O. acknowledges funding by the CPAN project. S.R.L. acknowledges funding by the U.S. National Science Foundation under Contract No. PHY-0758100. The authors thank Dr. L. Toker for her invaluable help preparing the figures for this manuscript., The low-energy structure of Co-65 was studied by means of gamma(-) and fast-timing spectroscopy at the ISOLDE/CERN facility. The known level scheme of Co-65 populated following the beta(-) decay of Fe-65 was expanded. The experimental results were compared with large-scale shell-model calculations. The measured long lifetime of the (1/2(1)(-)) level confirms its nature as a highly collective state with proton excitations across the Z = 28 gap and neutrons across the N = 40 subshell., Unión Europea. FP7, Ministerio de Economía y Competitividad (MINECO), Centro de Excelencia Severo Ochoa, Grupo de Física Nuclear (GFN-UCM), CPAN project, U.S. National Science Foundation, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

Mean lifetimes of yrast states of the isotopes Hf-174,Hf-176,Hf-178,Hf-180 have been measured using fast-electronic scintillation timing. Excited states of Hf-174,Hf-176,Hf-178 were populated via beta decay, while 180 Hf was populated via Coulomb excitation. The lifetimes of the 2(1)(+) and 4(1)(+) states of all isotopes and the lifetimes of the 6(1)(+) states of Hf-174,Hf-178 were measured, using the slope and the centroid shift methods. The mean lifetime, tau(4(1)(+)) = 85(13) ps, of Hf-178 has been determined for the first time. In addition, the mean lifetimes of the 2(1)(-) and the 3(1)(-) states of Hf-176 have been determined. Systematic uncertainties on the evolution of data as a function of neutron number were reduced by using the same setup for all the isotopes of interest. The data are in agreement with other recent lifetime measurements where available and shows a shift of the maximum of collectivity for the Hf isotopic chain from neutron midshell at N = 104 to N = 100.

Lifetimes of intermediate-spin states in two rotational bands of Zr-99 have been measured. These states were populated following the neutron-induced fission of U-235 at the PF1B beamline of the Institut Laue-Langevin, Grenoble, during the EXILL-FATIMA campaign. The nucleus Zr-99(59) exhibits shape coexistence and lies precisely on the border of an abrupt change in ground-state deformation when going from N = 58 to N = 60, making its study interesting for understanding the mechanisms involved in the rapid onset of deformation here. The B(E2) values extracted for decays in the nu 3/2[541] band allow quadrupole deformations of beta(2) = 0.34(1) and 0.26(3) to be determined for the 821.6- and 1236.6-keV members, whereas beta(2) = 0.32(3) was found for the 850.5-keV member of the nu 3/2[411] band. Some of the excited states known in Zr-99 have been reasonably described with interacting boson-fermion model (IBFM) calculations. Type-II shell evolution is proposed to play a major role in modifying single-particle energies in Zr-99.

The half-life of the 15/ 2(1)(+) state of the 3-valence-proton nucleus I-135 has been measured to be 1.74(8) ns using the EXILL-FATIMA mixed array of Ge and LaBr3 detectors. The nuclei were produced following the cold neutron-induced fission of a U-235 target at the PF1B beam line of the Institut Laue-Langevin. The extracted B(E2; 15/2(+) -> 11/2(+)) value enabled a test of seniority relations for the first time between E2 transition rates. Large-scale shell-model calculations were performed for Te-134 and I-135, and reinterpreted in a single-orbit approach. The results show that the two-body component of the E2 operator can be large whereas energy shifts due to the three-body component of the effective interaction are small.

The existence of two close-lying nuclear states in Ga-73 has recently been experimentally determined: a 1/2(-) spin-parity for the ground state was measured in a laser spectroscopy experiment, while a J(pi\) = 3/2(-) level was observed in transfer reactions. This scenario is supported by Coulomb excitation studies, which set a limit for the energy splitting of 0.8 keV. In this work, we report on the study of the excited structure of Ga-73 populated in the beta decay of Zn-73 produced at ISOLDE, CERN. Using beta-gated, gamma-ray singles, and gamma-gamma coincidences, we have searched for energy differences to try to delimit the ground-state energy splitting, providing a more stringent energy difference limit. Three new half-lives of excited states in Ga-73 have been measured using the fast-timing ;method with LaBr3(Ce) detectors. From our study, we help clarify the excited structure of Ga-73 and we extend the existing Zn-73 decay to Ga-73 with 8 new energy levels and 35 gamma transitions. We observe a 195-keV transition consistent with a gamma ray de-exciting a short-lived state in the beta-decay parent Zn-73.c

The ROmanian array for Spectroscopy in HEavy ion REactions (ROSPHERE) has been designed as a multi detector setup dedicated to gamma-ray spectroscopy studies at the Bucharest 9 MV Tandem accelerator. Consisting of up to 25 detectors (either Compton suppressed HPGe detectors or fast LaBr3(Ce) scintillator detectors) together with a state of the art plunger device, ROSPHERE is a powerful tool for lifetime measurements using the Recoil Distance Doppler Shift (RDDS) and the in-beam Fast Electronic Scintillation Timing (FEST) methods. The array's geometry, detectors, electronics and data acquisition system are described. Selected results from the first experimental campaigns are also presented. (C) 2016 Elsevier B.V. All rights reserved.

The low-lying positive-and negative-parity states in Yb-168 have been investigated by means of the (alpha, 2n gamma) fusion evaporation reaction. Using the coincidence method, the level scheme was corrected and extended up to 3MeV, for both the positive-and negative-parity states. Using the new branching ratios determined in the present experiment, the K quantum number was proposed for two negative-parity bands by direct comparison with the Alaga rule. Like in some other nuclei, one negative-parity band was established, decaying predominantly to the gamma-vibrational band. In a second experiment, the lifetimes of the low-lying excited states up to J(pi) = 6(+) in the ground-state band were measured by using the in-beam fast-timing method with the Bucharest mixed high-purity germanium (HPGe) and LaBr3:Ce detector array using the triple-gamma coincidence method. Reduced E2 transition probabilities were extracted from the measured lifetimes and compared with the corresponding observables in neighboring isotopes, showing a smooth behavior with increasing mass. The positive-and negative-parity states as well as E1 and E2 transition probability ratios revealed by these experiments are compared with the interacting boson model in the sd and spdf boson space, and with the confined beta-soft rotor model, and are found to be in good agreement.