| As a special region in the nuclear structure studies,the N～50 region has attracted lots of interests of both experimentical and theorical scientists. For N=50 is a magical number for neutron, the nuclei in this region show some interesting characters such as isomer island, spherical shape, irregular de-excited energy. A great number of studies have revealed that the level structure in this region can be well reproduced by the shell model calculation. As the shell model can provide the configurations of the nuclear levels, it is helpful to study the mechanism of the emergency of the isomer in this region. The purpose of present work is to establish the level structure of the odd-odd nucleus 90Nb and odd-A nucleus 91Nb at high spin states using in-beam γspectroscopy. The double-odd nucleus 90Nb, with 41 proton and 49 neutron, has two valence nucleons outside the 88Sr core. i.e. one proton particle and one neutron hole in g9/2 orbital respectively. Xiangdong Ji and R.Gross's works have proved that for the low lying states of 90Nb, the shell model calculations are consistent with the experimental results. While for the odd-Z nucleus , there is only one valence proton particle at g9/2 orbital outside the 88Sr core. And the calculation performed before reproduce the experimental results of 91Nb as well. In present work,the high spin states of 90Nb and 91Nb were populated via reaction 76Ge(19F,Xn) at the beam energy of 80MeV. The 19F beam was delivered by the HI-13 tandem accelerator in the China Institute of Atomic Energy(CIAE). The target consists of a 2.2mg/cm2 layer of 76Ge enriched to 96% evaporating on a 10mg/cm2 lead backing. The beam energy was chosen to maximize the yield of 90Nb and 91Nb comparing to other nucleus populated in the same reaction. The γ-γcoincidence events were collected by a multi-detector array consisting of 14 HPGe detector with a BGO Compton suppression shield. A total of 68×106 events were collected in event-by-event mode. The γ-γcoincidence data were sorted offline into conventional Eγ-Eγmatrices and analyzed using the RADWARE package base on Linux-PC system. About 20 new γtransitions were assigned to 90Nb and 10 new ones were assigned to 91Nb. Someγtransitions were reversed in their placement in the level scheme of 91Nb.The spin and parity of the levels in the two nuclei were tentatively assigned according to the DCO ratios and systematical analysis. As the two nuclei were compared with their isotones for systematical analysis respectively, it shows that at high spin states, N～50 isotones were alike in their levels structure and the energy of levels at the same spin increased when the proton number decreased. this phenomena might be caused by the increasing of proton number makes the protons could be excited easily, in case that the states are dominated by the excited protons. Researches have showed that in this region when their neutron number N<44 ,the nuclei have a stable deformation, while there are some special nuclei which have a super deformation. When the neutron number increases(N=45,46), the competition of collective and particle excitation at high-spin states is expected . For N=47,48, there are still some evidence of collective motion at low-spin states, and the energy structure can be well described by shell model at high-spin states. While for those nuclei whose neutron number is N=49 or 50, even at low-spin states, the shell model calculation is in good accordance with the experimental results.
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