Structure Of Near-spherical Nucleus⁸⁸Y

The proton number and the neutron number of the nuclei in the A～80mass region are larger than the magic number28and smaller than the magic number50. There is fierce competition between the single-particle and collective degrees of freedom. Lots of complicated information of nuclear structure was found in this region. The shape of the nuclei will change much if the quasiparticle changes. Many nuclear physicists take great interest in the phenomena such as magnetic rotation, the chiral symmetry in these nuclei and so on.The high spin states of88Y were populated via heavy ion fusion evaporation reaction82Se(11B,5n)88Y at the beam energy of52MeV. The11B beam was delivered by the HI-13tandem accelerator at China Institute of Atomic Energy(CIAE). The target consisted of a1.35mg/cm2layer of82Se evaporated on a9.1mg/cm2Pb backing. The de-excited y rays from the reaction residues were detected by a multi-detector array, which consists of12Compton suppressed HPGe detectors and2planar HPGe detectors. A total of130×106two folds γ-γ coincidence events were accumulated.The experimental data were sorted into symmetrical matrix and two Angular Distribution of y rays Deexciting the Oriented States(ADO) matrix in the offline analysis. Finally, a new level scheme of88Y which includes30new y rays and20new energy levels was constructed. The spin and parity of new energy levels in88Y have been assigned on the basis of the ADO ratios. The positive-parity part of the level scheme has been extended to1=21+at the energy of9454.1keV and the negative-parity part has been extended to1=19at the energy of8627.7keV.The level structure of88Y shows typical feature of spherical nuclei, and its high-spin states were formed by the excitations of the quasi-particle coupling with the88Sr core. We have performed Semi-Emperical Shell Model (SESM) calculation on the levels of88Y, and most results were shown to well correspond to the experimental results.