The beta-ray angular correlations for the spin alignments of 8Li and 8B have been observed in order to test the conserved vector current (CVC) hypothesis. The alignment correlation terms were combined with the known beta-alpha-angular correlation ter
ms to determine all the matrix elements contributing to the correlation terms. The weak magnetism term, 7.5pm0.2, deduced from the beta-ray correlation terms was consistent with the CVC prediction 7.3pm0.2, deduced from the analog-gamma-decay measurement based on the CVC hypothesis. However, there was no consistent CVC prediction for the second-forbidden term associated with the weak vector current. The experimental value for the second-forbidden term was 1.0 pm 0.3, while the CVC prediction was 0.1 pm 0.4 or 2.1 pm 0.5.
The low-lying states in 106Zr and 108Zr have been investigated by means of {beta}-{gamma} and isomer spectroscopy at the RI beam factory, respectively. A new isomer with a half-life of 620pm150 ns has been identified in 108Zr. For the sequence of eve
n-even Zr isotopes, the excitation energies of the first 2+ states reach a minimum at N = 64 and gradually increase as the neutron number increases up to N = 68, suggesting a deformed sub-shell closure at N = 64. The deformed ground state of 108Zr indicates that a spherical sub-shell gap predicted at N = 70 is not large enough to change the ground state of 108Zr to the spherical shape. The possibility of a tetrahedral shape isomer in 108Zr is also discussed.
