Test of the generalized Brink-Axel hypothesis in ⁶⁴ ⁶⁵Ni

Previously published particle-γ coincidence data on the 64Ni(p,p′γ) 64Ni and 64Ni(dpγ)65Ni reactions were further analyzed to study the statistical properties of γ decay in64, 65Ni. To do so, the γ-decay to the quasicontinuum region and discrete low-lying states was investigated at γ -ray energies of 2.0–9.6 and 1.6–6.1 MeV in 64 Ni and 65 Ni, respectively. In particular, the dependence of the γ-strength function with initial and final excitation energy was studied to test the validity of the generalized Brink-Axel hypothesis. Finally, the role of fluctuations in transition strengths was estimated as a function of γ-ray and excitation energy. The γ-strength function is consistent with the hypothesis of the independence of initial excitation energy, in accordance with the generalized Brink-Axel hypothesis. The results show that the γdecay to low-lying levels displays large fluctuations for low initial excitation energies.We are also grateful for the financial support received from the Research Council of Norway (NFR). S.S. and G.M.T. acknowledge funding under NFR project Grants No. 210007 and No. 262952/F20. A.C.L. acknowledges financial support from the ERC-STG2014 under Grant No. 637686

Observation of low-lying resonances in the quasicontinuum of 195,196Pt and enhanced astrophysical reaction rates

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Nuclear level densities and gamma-ray strength functions of 145,149,151Nd isotopes

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Nuclear level densities and γ -ray strength functions of 180,181Ta and neutron capture cross sections

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Resonances in odd-odd 182Ta

Abstract: Enhanced γ -decay on the tail of the giant electric dipole resonance, such as the scissors or pygmy resonances, can have significant impact on (n,γ ) reaction rates. These rates are important input for modeling processes that take place in astrophysical environments and nuclear reactors. Recent results from the University of Oslo indicate the existence of a significant enhancement in the photon strength function for nuclei in the actinide region due to the scissors resonance. Further, the M1 strength distribution of the scissors resonances in rare earth nuclei has been studied extensively over the years. To investigate the evolution and persistence of the scissor resonance in other mass regions, an experiment was performed utilizing the NaI(Tl) γ -ray detector array (CACTUS) and silicon particle telescopes (SiRi) at the University of Oslo Cyclotron laboratory. Particle-γ coincidences from the 181Ta(d,p)182Ta and 181Ta(d,d’)181Ta reactions were used to measure the nuclear level density and photon strength function of the well-deformed 181Ta and 182Ta systems, to investigate the existence of resonances below the neutron separation energy

Beta-gamma spectroscopy of the neutron-rich 150Ba

International audience; Excited states in the neutron-rich nucleus 150Ba have been observed via β–γ spectroscopy at the Radioactive Isotope Beam Factory, RIKEN Nishina Center. The 150Ba ions were produced by the in-flight fission of a 238U beam with an energy of 345 MeV/nucleon. The E(2+) energy of 150Ba was identified at 100 keV, which is the lowest known in the neutron-rich Ba isotopes. A γ -ray peak was also observed at 597 keV. A mean-field calculation with a fully 3D real space was performed and a static octupole deformation was obtained for the Ba isotopes. Kπ = 0− and 1− excited states with significant octupole collectivity were newly predicted at around or lower than 1 MeV on the ground state of 150Ba by a random-phase approximation calculation. The 597 keV γ ray can be interpreted as a negative-parity state, showing that 150Ba may possess octupole collectivity

Probing the nuclear structure in the vicinity of

Theoretical and experimental studies of neutron-rich nuclei have shown that the general concept of shell structure is not as robust and universal as earlier thought, but can exhibit significant changes as a function of neutron excess. New magic numbers appear and some other conventional ones disappear mainly because of a different ordering of the single-particle orbitals. In the present contribution, recent experimental studies of neutron-rich Cu isotopes, performed at RIKEN using β decay and one-proton knockout reactions, will be discussed. Neutron-rich nuclei near 78Ni were populated through in-flight fission of 238U on thick 9Be targets in both experiments. In the β-decay study, 75,77Ni nuclei were implanted into the WAS3ABi silicon array, while γ rays from excited states in 75,77Cu emitted after β decay of the implanted ions were detected with the EURICA Ge detector array that was surrounding the active stopper. In a second experiment within the SEASTAR campaign at RIKEN, the same 75,77Cu nuclei were produced in (p,2p) knockout reactions from 76,78Zn beam particles at around 250 MeV/nucleon impinging onto the MINOS liquid hydrogen target. In the latter experiment the DALI2 NaI array was used to detect de-excitation γ rays measured in coincidence with Cu nuclei identified in the Zero Degree Spectrometer. Both studies are complimentary and greatly contribute to our understanding on the nuclear structure in the 78Ni region

Probing the nuclear structure in the vicinity of 78Ni

Theoretical and experimental studies of neutron-rich nuclei have shown that the general concept of shell structure is not as robust and universal as earlier thought, but can exhibit significant changes as a function of neutron excess. New magic numbers appear and some other conventional ones disappear mainly because of a different ordering of the single-particle orbitals. In the present contribution, recent experimental studies of neutron-rich Cu isotopes, performed at RIKEN using β decay and one-proton knockout reactions, will be discussed. Neutron-rich nuclei near 78Ni were populated through in-flight fission of 238U on thick 9Be targets in both experiments. In the β-decay study, 75,77Ni nuclei were implanted into the WAS3ABi silicon array, while γ rays from excited states in 75,77Cu emitted after β decay of the implanted ions were detected with the EURICA Ge detector array that was surrounding the active stopper. In a second experiment within the SEASTAR campaign at RIKEN, the same 75,77Cu nuclei were produced in (p,2p) knockout reactions from 76,78Zn beam particles at around 250 MeV/nucleon impinging onto the MINOS liquid hydrogen target. In the latter experiment the DALI2 NaI array was used to detect de-excitation γ rays measured in coincidence with Cu nuclei identified in the Zero Degree Spectrometer. Both studies are complimentary and greatly contribute to our understanding on the nuclear structure in the 78Ni region