Search

The excited states in the light nucleus 9Be are studied through β-delayed neutron decays from spin-polarized 9Lig.s.. The neutron transitions via 5Heg.s. from the 2.43-, 2.78-, 4.704-, 5.59-, and 7.94-MeV states in 9Be are observed for the first time, and the spins and parities (Iπ's) of the excited states in 9Be are assigned from β-n coincidences and measurements of the β-decay asymmetries. The spin parity, Iπ, of the 2.43-MeV state is assigned to be 5/2-, which is consistent with the reported value. The present results suggest that the Iπ values of the 2.78-, 4.704-, 5.59-, and 7.94-MeV states are 3/2-, 1/2-, 5/2-, and 3/2-, respectively, which are different from early reported values. However, shell-model calculations of the p shell are in overall good agreement with the present results, except for the Iπ values of the 2.78- and 4.704-MeV states. [ABSTRACT FROM AUTHOR]

As the first step of systematic studies on neutron-rich Mg isotopes, the structure of 28Mg has been investigated by β-decay spectroscopy of spin-polarized 28Na at TRIUMF. Spin-parity assignments have been successfully performed for levels in 28Mg by taking advantage of the anisotropic β decay. Previous assignments for three levels were reconfirmed. New assignments were performed for four levels including a newly found 2+ level at 7.461 MeV. The experimental results were compared, on a level-by-level basis, with the shell-model calculation in the model space restricted to the sd shell. Overall good agreement between the experimental and theoretical results indicates dominance of the normal configurations in most of the 28Mg levels. High performance of the present method promises successful application to heavier Mg isotopes to elucidate the shell evolution in the region of the N = 20 island of inversion [ABSTRACT FROM AUTHOR]

High-spin states in the odd-odd nucleus 136La, which is located close to the β-stability line, have been investigated in the radioactive-beam-induced fusion-evaporation reaction 124Sn(17N,5n). The use of the radioactive beam enabled a highly sensitive and successful search for a new isomer [14+, T1/2 = 187(27) ns] in l36La. In the A = 130-140 mass region, no such long-lived isomer has been observed at high spin in odd-odd nuclei. The 136La level scheme was revised, incorporating the 14+ isomer and six new levels. The results were compared with pair-truncated shell model (PTSM) calculations which successfully explain the level structure of the Πh11/2 ⊗ vh11/2-1bands in 132La and 134La. The isomerism of the 14+ state was investigated also by a collective model, the cranked Nilsson-Strutinsky (CNS) model, which explains various high-spin structures in the medium-heavy mass region. It is suggested that a new type of collective structure is induced in the PTSM model by the increase of the number of Πg7/2 pairs, and/or in the CNS model by the configuration change associated with the shape change in 136La. [ABSTRACT FROM AUTHOR]

The l35La nucleus has been studied using the fusion-evaporation reaction 124Sn(17N,6n) induced by the l7N radioactive beam. The level scheme has been constructed from the y-y coincidence measurement with an array of 12 HPGe detectors, and the lifetimes of two previously known isomeric states has been deduced. The transitions and their intensities observed in the current work as well as the level scheme derived frôm them is in agreement with the results, of a recently published work; However, our interpretation of the results differs significantly in terms of spin and parity assignments, thus solving various contradictions concerning the configurations of some of the bands discussed in the aforementioned work. [ABSTRACT FROM AUTHOR]

Excited states in 17C were investigated through the measurement of β-delayed neutrons and γ rays emitted in the β decay of 17B. In the measurement, three negative-parity states and two inconclusive states were identified in 17C above the neutron threshold energy, and seven γ lines were identified in a β-delayed multiple neutron emission of the 17B β decay. From these transitions, the β-decay scheme of 17B was determined. In particular, a de-excitation 1766-keV γ line from the first excited state of 16C was observed in coincidence with the emitted β-delayed neutrons, and this changes the previously reported β-decay scheme of 17B and level structure of 17C. In the present work, the β-NMR technique is combined with the β-delayed particle measurements using a fragmentation-induced spin-polarized 17B beam. This new scheme allows us to determine the spin parity of β-decay feeding excited states based on the difference in the discrete β-decay asymmetry parameters, provided the states are connected through the Gamow-Teller transition. In this work, Iπ=1/2-, 3/2-, and (5/2-) are assigned to the observed states at Ex= 2.71(2), 3.93(2), and 4.05(2) MeV in 17C, respectively. [ABSTRACT FROM AUTHOR]