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Research on High Spin States in Neutron-Rich 108,112Ru and Neutron-Deficent 134,135Ba Nuclei

Author: CheXingLai
Tutor: ZhuShengJiang
School: Tsinghua University
Course: Physics
Keywords: high-spin states γ-γcoincidence collective backbending configuration systematic comparison
CLC: O571.22
Type: PhD thesis
Year: 2007
Downloads: 141
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As one of the forefront fields in nuclear physics, research on high spin states can provide valuable information about nuclear structure, nuclear shape, and nucleon coupling and so on. In this thesis, we have studied the structural characteristics of the high spin states in 108Ru and 112Ru at neutron rich A~100 region and 134Ba and 135Ba at neutron-deficient A~130 region.The high spin states of 108Ru and 112Ru were studied by measuring the promptγ-rays in spontaneous fission of 252Cf. The experiment was carried out at the Lawrence Berkeley National Laboratory (U.S.A). The triple- and higher-fold coincidence events were collected. The high spin state experiment of 134Ba and 135Ba was performed at HI-13 Tandem Accelerator in China Institute of Atomic Energy by using heavy ion induced reaction 130Te(9Be,xn) at a bean energy of 45MeV. Theγ-γcoincidence measurements were performed.For 108,112Ru nuclei, the ground-state band and the one-phononγ-vibrational band have been confirmed and extended. A two-phononγ-vibrational band and a two-quasiparticle band have been observed in both nuclei. The structural characteristics of the collective bands were studied. The cranked shell model (CMS) calculations indicate that both 108Ru and 112Ru nuclei have triaxial deformation and the band crossing in the yrast band in these two nuclei is due to the alignment of a pair of h11/2 neutrons. The characters of the one-phonon and two-phononγ-vibrational bands in 108,112Ru have been discussed based on the systematics. Through systematic comparison and calculated Nilsson diagram, the two-quasiparticle bands are most probably built on theν{[402]5/2+?[532]5/2-}5- configuration in 108Ru andν{[402]5/2+?[523]7/2-}6- configuration in 112Ru, respectively.The level scheme in 134Ba has been updated with spin up to 20 , and many levels and transitions above the 10+ isomer have been identified. The CSM calculations indicate that the back-bending of 134Ba is caused by alignment of a pair of h11/2 quasi-neutrons. Based on the systematical analyzing, the 10+ isomer in 134Ba is an yrast trap, that is, it has prolate deformation withγ≈-120°which is originated from two neutron configuration. Above the 10+ isomer level, the levels show strong single-particle motion character.The level scheme in 135Ba based on the 11/2- isomer has been expanded up to 35/2 . Twenty new levels and twenty four new transitions were identified. At the low spins, the yrast collective structure built on the 11/2- multiplet may show a triaxial shape withγ>30°according to the systematical behavior observed in neighboring nuclei as well as the calculations of the triaxial rotor-plus-particle model. The calculated deformation parameter areε=0.09,γ=33.6°. This indicates that the transition from the prolate side (γ<30°) in N≤77 to the oblate side in N≥79 (γ>30°) occurs in the Ba isotopes, as observed in the neighboring isotopes. The configurations for six high spin levels have been assigned from a systematical comparison with neighboring isotones.

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CLC: > Mathematical sciences and chemical > Physics > Nuclear physics,high energy physics > Nuclear physics > The structure and nature of the nucleus > Properties and determination of
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