Collective band structures in the Tc-99 nucleus
Collective band structures in the Tc-99 nucleus
复制标题
Tc-99 原子核中的集体能带结构
DOI：
10.1103/physrevc.91.054314
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发表时间：
2015-05
影响因子：
3.1
通讯作者：
Wu Y. H.
中科院分区：
文献类型：
--
作者：
Li H. J.;Xiao Z. G.;Zhu S. J.;Patial M.;Qi C.;Cederwall B.;Zhang Z.;Wang R. S.;Yi H.;Yan W. H.;Cheng W. J.;Huang Y.;Lyu L. M.;Zhang Y.;Wu X. G.;He C. Y.;Zheng Y.;Li G. S.;Li C. B.;Li H. W.;Liu J. J.;Luo P. W.;Hu S. P.;Wang J. L.;Wu Y. H.
尽管距欧内斯特·卢瑟福和他的同事首次发现原子核已经有100多年了，但原子核的许多特征仍然是我们无法理解的。核成分之间的基本相互作用；核子，最终是夸克，还没有被详细了解，核多体系统的复杂性使实验数据的理论解释面临巨大挑战。因此，重要的是要把重点放在不同的现象上，在这些现象上，实验测量结果可以与理论预测相比较，从而提供严格的理论检验。其中一个领域是与原子核整体的旋转和振动有关的集体激发的核现象学，以及这种激发模式如何从占据封闭壳层外单粒子轨道的几个核子之间的相互作用中发展出来。本文对99Tc、162W和166Re核的激发态进行了实验研究。这些原子核位于Segre图的“过渡”区域，当在封闭的中子和质子壳层外添加价核子时，集体激发机制开始变得重要。这样的核对于检验最先进的理论模型很重要。本工作研究的原子核激发态是用重离子聚变蒸发反应填充的。在本工作之前，99Tc的高自旋数据仍然缺乏，因为在之前的工作中[1-5]激发态只填充到3mev左右。本文将两个集体带扩展到中间角动量态。将实验结果与其他同位素系统进行了比较，并基于半经典计算和粒子转子模型评估了其电磁特性。162W和166Re核位于中子非常缺乏的160-170质量区域，需要特殊的技术来识别它们的激发态结构。162W的能级方案最早由Dracoulis等人于1993年提出，其中第一个激发态2+被指定在基态以上450 keV。然而，由于缺乏选择性，使得γ射线对162W较高能级的识别不确定。本文采用高选择性的反冲衰变标记技术，对162W激发态的γ射线跃迁进行了唯一识别，并构建了其能级格式。此外，该实验装置还能精确测定162W α-衰变基态的半衰期。从半衰期的测量中提取了162W的α-形成概率，并与邻近原子核进行了系统比较。首次在166Re中发现了两个类旋转带，并利用反冲距离多普勒频移法测量了带(1)中最低三个激发态的寿命。将计算结果与基于半经典方法、粒子转子模型和相对论平均场方法的倾斜轴曲柄模型的理论计算结果进行了比较。在总罗思曲面预测和曲柄壳模型计算的框架下，解释了旋转带的微观机理（结构和排列等）。
Despite that it is more than 100 years since the atomic nucleus was first dis- covered by Ernest Rutherford and coworkers, many of its features still elude our understanding. The fact that the fundamental interactions between the nuclear constituents; nucleons, and ultimately quarks, are not yet known in detail, and the complexity of the nuclear many-body system compound the great challenges facing theoretical interpretations of experimental data. It is therefore important to focus on distinct phenomena where experimental mea- surements can be compared with theoretical predictions, providing stringent tests of theory. One such area is the nuclear phenomenology of collective excitations related to rotations and vibrations of the nucleus as a whole, and how such modes of excitation may develop from the interactions between a few nucleons occupying single-particle orbits outside closed shells.This thesis is devoted to experimental studies of excited states in the 99Tc, 162W, and 166Re nuclei. These nuclei lie in “transitional” regions of the Segre chart, where collective excitation mechanisms start becoming important when adding valence nucleons outside closed neutron and proton shells. Such nuclei are important for testing state-of-the-art theoretical models. The excited states of the nuclei studied in the present work were populated using heavy-ion fusion-evaporation reactions. Prior to the present work, high-spin data were still lacking in 99Tc since in the previous works [1–5] excited states were only populated up to around 3 MeV. Two collective bands have been extended to intermediate angular momentum states in the present work. The experimental results were compared with the systematics of other technetium isotopes, evaluating electromagnetic characteristics based on semiclassical calculations and the particle-rotor model. The 162W and 166Re nuclei are situated in the very neutron-deficient 160-170 mass region, requiring special techniques for identifying their excited-state structures. The level scheme of 162W was first reported by Dracoulis et al. in 1993 [6], where the first excited 2+ state was assigned to be 450 keV above the ground state. However, the lack of selectivity made the γ-ray identification for higher energy levels of 162W uncertain. In this work, the highly selective recoil-decay tagging technique was used to uniquely identify γ-ray transitions from excited states in 162W and to construct its level scheme. In addition, the experimental setup enabled a precise determination of the half-life of the α-decaying ground state of 162W. The α-formation probability for 162W was extracted from the measurement of the half-life and systematical comparisons with the neighboring nuclei were performed. Two rotational-like bands were identified in 166Re for the first time and the lifetimes of the lowest three excited states in band (1) were measured using the recoil distance Doppler shift method. The results were compared with theoretical calculations based on a semiclassical approach, the particle-rotor model, and the tilted axis cranking model in a relativistic mean field approach. The microscopic mechanisms (configuration and alignment, etc) of the rotational bands were interpreted under the framework of total Routhian surface predictions and cranked shell model calculations.