Research On High Spin States In ～(137)La,～(138)Pr And ～(98)Sr Nuclei

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. The major content in this dissertation is the research on the high spin states of ¹³⁷La, ¹³⁸Pr and ⁹⁸Sr.The experiments of ¹³⁷La and ¹³⁸Pr were performed at HI-13 Beijing Tandem Accelerator in China Institute of Atomic Energy. The high-spin states in ¹³⁷La and ¹³⁸Pr were populated with heavy-ion fusion reactions 130Te(11B, 4n)136La at a bean energy of 50 MeV and ¹²⁸Te(¹⁴N, 4n)¹³⁸Pr at a bean energy of 64 MeV, respectively. Theγ-γcoincidence measurements were carried out using an array of fourteen Compton-suppressed Ge detectors in both the experiments. Approximately 3.6×10⁸ and 2.3×10⁸ coincidence events were collected, respectively.The level scheme of ¹³⁷La has been expanded with spin up to 33/2(?) . All the levels and transitions above the 15/2^- level, including 27 levels and 37 transitions, were newly identified. Four new bands have been found in the nucleus. In the collective band based on the 17/2^- level, whose configuration is assigned asÏ€d_5/2(?)νd_3/2^-1h_11/2^-1, a collective backbending has been observed at a rotational frequency of(?)ω≈0.48 MeV. From systematic comparison and cranked shell model (CSM) calculations, the collective backbending probably originates from the alignment of a pair of protons. The band built on 25/2^- level with strong M1 transitions is proposed as a collective oblate band withγ≈-60°.For ¹³⁸Pr, the new level scheme has been established. According to systematic comparison, the spins of the yrast band have been newly assigned. Five oblate bands were identified, and two of them were newly observed. We analyzed the signature inversion and aligned angular momentum ofÏ€h_11/2(?)νh_11/2 band. Based on cranked shell model (CSM) calculations andsystematic comparison, the backbending ofÏ€h_11/2(?)νh_11/2 band originates probably by the alignment of protons. The moments of inertial of five oblate bands were analyzed, and their possible configurations were proposed.Rotational bands in neutron-rich ⁹⁸Sr nucleus have been investigated by measuring high-fold promptγ-ray coincidence events of the spontaneous fission of ²⁵²Cf with the Gammasphere detector array. A deformed K=3 band built on 1838 keV level has been confirmed and extended. Another deformed K=6 band based on 2535 keV level has been established. Both bands originate most probably from theν9/2[404](?)ν3/2[411] two-quasiparticle configuration withΩ=|Ω₁-Ω₂| andΩ=|Ω₁+Ω₂|, respectively. These two bands form the so-called Gallagher-Moszkowski (GM) doublet. The moments of inertial and spin alignments of the two bands have been discussed. Based on the delay-coincidence measurements, the half-lives for the K=3 and K=6 band head levels have been obtained to be 13±3 ns and 4.5±1.0 ns, respectively.