【作者】 李明亮；

【导师】 朱胜江；

【作者基本信息】 清华大学 ， 物理学， 2006， 博士

【摘要】 原子核高自旋态研究是核物理研究的一个重要的前沿领域，它为人们认识和理解核结构、核形状、核子耦合等特性提供了非常有价值的信息。本论文内容为研究¹³⁷La、¹³⁸Pr和⁹⁸Sr的高自旋态结构特性。对¹³⁷La和¹³⁸Pr高自旋态的实验研究是在中国原子能科学研究院的HI-13串列加速器上进行的，分别通过重离子融合－蒸发反应¹³⁰Te(¹¹B，4n)与¹²⁸Te(¹⁴N，4n)来布居¹³⁷La与¹³⁸Pr的高自旋态，束流能量分别为50MeV和64MeV。在这两个实验中，均用14个反康高纯Ge探测器，测量两重以上符合事件，分别获得总记数为3.6×10⁸与2.3×10⁸个等效的两重γ-γ符合事件。对¹³⁷La核，研究结果将它的能级纲图扩展到33/2（?），新识别了27个能级和37条跃迁，发现了三条较清晰的集体转动带。基于17/2-能级的集体带，其准粒子组态被指定为πh_5/2（?）νd_3/2^-1h_11/2^-1，在转动频率（?）ω≈0.48MeV处发生集体回弯。通过系统学比较和推转壳模型计算，认为该集体回弯由一对质子的顺排引起。通过对建立在25/2^-能级上的一个集体带的分析表明，它是一个扁椭形变带（γ≈-60°）。对138Pr核，建立了新的能级纲图。根据系统学分析，重新指定了晕带的自旋。识别了5条扁椭形变带（γ≈-60°），其中两条是新建立的。对πh_11/2（?）νh_11/2带的旋称反转、顺排角动量进行了分析。根据推转壳模型计算和系统学比较，认为一对质子顺排引起了πh_11/2（?）νh_11/2带的回弯。分析了五条扁椭带的两类转动惯量，分别指定了它们可能的组态。通过对²⁵²Cf的自发裂变产生的瞬发谱的分析，对丰中子核⁹⁸Sr的集体转动带进行了研究。扩展了建立在1838keV能级上的K=3的转动带。新发现了一条建立在2535keV能级上的K=6的转动带。通过分析，这两条带的组态都是是ν9/2[404]（?）ν3/2[411]，分别满足Ω=|Ω₁-Ω₂|和Ω=|Ω₁+Ω₂|的耦合关系，构成一对Gallagher-Moszkowski（GM）伙伴带。研究了这两条带的转动惯量和顺排角动量特征。用延迟符合方法，测得K=3和K=6的两个带带头能级的半衰期分别是13±3ns和4.5±1.0ns。更多还原

【Abstract】 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 asπd_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 ofπh_11/2（?）νh_11/2 band. Based on cranked shell model （CSM） calculations andsystematic comparison, the backbending ofπh_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.更多还原