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Spin-polarized radioactive nuclear beams at TRIUMF enable a new spectroscopic method which efficiently assigns spins and parities of the daughter levels by taking advantage of the asymmetric β-decay of the polarized parent nucleus. This method was successfully applied to structure studies of 29Mg and 30Mg in connection with the physics of the “island of inversion”. In 29Mg, two low-lying levels with intruder configuration were assigned. In 30Mg, coexistence of spherical shape, prolate shape and γ-collectivity was strongly suggested. [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]

The high-spin isomer in 151Er ( Ex = 10.3 MeV, T1/2 = 420 ns) has been studied by the 116Sn ( 40Ar , 5n) 151Er reaction at 197MeV. From the $ \gamma$ $ \gamma$ coincidence relations, a new transition with an energy of 1514keV was found. This finding requires the revision of the spin-parity assignment from previous 67/2- to 61/2+ or 65/2- . The 61/2+ assignment is the one which was predicted by the deformed independent particle model as an isomer with a large oblate deformation ( $ \beta$ = - 0.17of the $\ensuremath[\nu(f_{7/2}h_{9/2} i_{13/2}) \pi(h^4_{11/2})]_{61/2^+}$ configuration. The isomerism may be attributed to the sudden shape change of the isomer from the nearly spherical shape of the lower-spin yrast states to the oblate shape. [ABSTRACT FROM AUTHOR]