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The structure of excited states in the neutron-rich nucleus 31 Mg, which is in the region of the “island of inversion” associated with the neutron magic number N = 20 , is studied by β – γ spectroscopy of spin-polarized 31 Na. Among the 31 Mg levels below the one neutron separation energy of 2.3 MeV, the spin values of all five positive-parity levels are unambiguously determined by observing the anisotropic β decay. Two rotational bands with K π = 1 / 2 + and 1 / 2 − are proposed based on the spins and energies of the levels. Comparison on a level-by-level basis is performed between the experimental results and theoretical calculations by the antisymmetrized molecular dynamics (AMD) plus generator coordinate method (GCM). It is found that various nuclear structures coexist in the low excitation energy region in 31 Mg. [ABSTRACT FROM AUTHOR]

Abstract: The excited states in the light neutron-rich nucleus 11Be have been studied through the β-delayed neutron- and γ-decays from spin-polarized 11Lig.s.. The level scheme and decay scheme of 11Be∗ are established from the β–γ, β–n and β–n–γ coincidences, and the spins and parities for 7 levels in 11Be are firmly assigned from the β-decay asymmetries measured in coincidence with the delayed radiations. The neutron-spectroscopic factors of the levels in 11Be are also determined. Some of the levels show good accord with predictions by the anti-symmetrized molecular dynamics (AMD) theory, which predicts various types of 2α-cluster states in the rotational bands and a single α-cluster state. [Copyright &y& Elsevier]

We have developed a polarized 3He ion source named “SEPIS” (spin-exchange polarized ion source) at RCNP, and Department of Physics, Osaka Univeristy. The SEPIS uses a large spin-exchange cross section, σse, and a small electron capture cross section,σec, for the 3He++Rb system theoretically expected at low 3He+ incident energies. The validity of SEPIS was experimentally proven by observing the 3He+ nuclear polarization as a function of the incident 3He+ energy. [ABSTRACT FROM AUTHOR]

Experiments based on the isomer-spectroscopy method were performed using the secondary beam line at RCNP, Osaka University. Recently, a new γ-ray spectroscopy method was established using fusion reaction induced by low-energy RI beam. This method enables us to study high-spin states of nuclei in wider mass region where it is difficult to populate them by using the combination of stable beams and stable targets. This method works well although low production of nuclei, because (1) the combination of beams and targets can be selected with large-reaction cross section and (2) high-S/N measurement can be performed by the event-by-event detection to select the events correlated with RI beam, which reduces background γ rays, competing with γ rays emitted from fusion products. As the first step, high-spin states of 142Pr were studied using fusion reaction induced by low-energy 17N RI beam. Large cross section was obtained by the 130Te(17N,5n) reaction with 4.9 MeV/u 17N beam. Event selection, which was carried out by the event-by-event detection with low-beam intensity of 2×104 pps, enables high-S/N measurement. [ABSTRACT FROM AUTHOR]

The level structures of 28Mg and 29Mg have been investigated by the β-decay of spin-polarized28Na and 29Na at ISAC, TRIUMF. The detailed β-γ and γ-γ coincidence measurements were performed. New γ rays and β transitions were observed both in 28Mg and 29Mg. We have succeeded in assigning spins and parities of many levels in 28Mg and 29Mg. Comparison with shell model calculations using USD Hamiltonian suggest that the structure of 28Mg and 29Mg are well explained in the sd-shell configurations, except for two levels at 1.095 and 1.430 MeV in 29Mg. This suggests negative parity assignments for these levels. The evolution of sd-pf shell is discussed. [ABSTRACT FROM AUTHOR]