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The nuclear structure of 66Se, nucleus beyond the N = Z line on the proton-rich side of the valley of stability, was investigated by the neutron knock-out reaction 67Se(12C,X)66Se using a 12C target. The analysis of the singles spectrum of the γ -rays emitted during the de-excitation of the populated low-lying excited states revealed two previously detected (927(4) keV, 1460(32) keV) and three new (744(6) keV, 1210(17) keV, 1661(23) keV) transitions. The 744-keV, the 1210-keV, and the 1460-keV transitions were found to be in coincidence with the one at 927 keV. The spectrum coincident with the 927-keV transition showed a further possible transition at 299(35) keV, which was obscured by significant atomic background in the singles spectrum. This transition might correspond to a peak previously reported at 273(5) keV that could not be assigned to 66Se unambiguously. Based on a comparison of the experimental data to theoretical calculations, four new excited states are proposed which suggest that 66Se exhibits shape coexistence. [ABSTRACT FROM AUTHOR]

Lifetimes of excited states in the very exotic nuclides 108Zr 68 and 110Zr 70 were measured for the first time applying high-resolution in-beam γ -ray spectroscopy at relativistic energies. The experiment was carried out at the Radioactive Isotope Beam Factory in RIKEN, using nucleon removal reactions of radioactive Nb ions to produce 108Zr and 110Zr. Emitted γ rays from the excited states were measured by the High-resolution Cluster Array at RIBF (HiCARI) and lifetimes were extracted from the observed line shapes caused by relativistic Doppler-shift effects. In addition to the new lifetime information, the precision of the E (2 1 +) and R 4 / 2 = E (4 1 +) / E (2 1 +) values of 110Zr could be significantly improved. The low-lying 2 2 + states in both nuclei are also newly observed, which are indicative of the triaxiality. The various physical quantities were compared with theoretical models to investigate the collectivity in Zr isotopes towards N = 70. Together the experimental and theoretical results point at a reduction of the axial deformation while triaxial collectivity increases. [ABSTRACT FROM AUTHOR]

Excited states in 98Ru were investigated using γ -ray spectroscopy following the β -decay of 98Rh, and via the 100Ru(p , t) reaction. Combining the results from the two experiments, two states were revised to have spin-parity of 4 + and subsequently assigned to the 0 2 + and " γ " bands, respectively. The observed structures in 98Ru are suggested to be deformed and rotational, rather than spherical and vibrational, and fit well into the systematics of these excitations in the Ru isotopes. The 0 2 + excitation is suggested as a shape coexisting configuration. This observation eliminates some of the last remaining candidates for nearly harmonic vibrational nuclei in the Z ≈ 50 region. Beyond-mean-field calculations are presented that support shape coexistence throughout the Ru isotopes with N = 52 –62, and suggest a smooth evolution of the shapes. [ABSTRACT FROM AUTHOR]

Excited states in the N = 40 isotone 62Ti were populated via the 63V (p , 2 p) 62Ti reaction at ∼200 MeV/nucleon at the Radioactive Isotope Beam Factory and studied using γ -ray spectroscopy. The energies of the 2 1 + → 0 gs + and 4 1 + → 2 1 + transitions, observed here for the first time, indicate a deformed 62Ti ground state. These energies are increased compared to the neighboring 64Cr and 66Fe isotones, suggesting a small decrease of quadrupole collectivity. The present measurement is well reproduced by large-scale shell-model calculations based on effective interactions, while ab initio and beyond mean-field calculations do not yet reproduce our findings. The shell-model calculations for 62Ti show a dominant configuration with four neutrons excited across the N = 40 gap. Likewise, they indicate that the N = 40 island of inversion extends down to Z = 20 , disfavoring a possible doubly magic character of the elusive 60Ca. [ABSTRACT FROM AUTHOR]