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Single-particle structure in neutron-rich isotopes

富中子同位素中的单粒子结构

基本信息

批准号：
PP/F000464/1
负责人：
Sean J Freeman
金额：
$ 19.32万
依托单位：
University of Manchester
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2007
资助国家：
英国
起止时间：
2007 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=PP%2FF000464%2F1
关键词：
Single particle structure neutron rich

项目摘要

A fundamental way of understanding the structure of the atomic nucleus is to consider the motion of its constituent particles, protons and neutrons, under the influence of the individual interactions between them. These so-called ab-initio calculations are difficult in all but the lightest nuclei due to increasing complexity as the number of constituents gets larger. Approaches that consider the motion of individual particles in the average field generated by all the other particles have enjoyed some success in near stable nuclei, when corrections or residual interactions are included. Such success is actually rather limited as the number of stable systems is very small in comparison with the total number of bound isotopes, but despite this such methods appear frequently even in student textbooks, giving an air of permanence and solidity to the theories. However, with increasing experimental sophistication, new effects have been found that only become apparent when studying single-particle structures over a wide range of neutron excess. Such changes in single-particle structures are surprising within the context of these models; for example, in some cases they disturb even the 'well-known' sequence of magic numbers dervived for stable systems. But they also have deeper consequences since the underlying single-particle nature of a nucleus dramatically effects other properties such as the nuclear shape and the existence and type of other excitation modes like collective vibrations and rotations of the whole nucleus. This grant proposal aims to study two aspects of single-particle structure. Firstly to investigate the mechanisms which may be responsible for the changes that are being uncovered. These can be related directly back to the force between two nucleons. It has been suggested that some of these changes are due to the tensor component of this force; this is particularly interesting if substantiated as there are only a few direct manifestations of this component in nuclear structure. Secondly the proposal aims probe a region of exotic nuclei where calculations based on the single-particle structure extrapolated rather crudely from stable systems predict some interesting new phenomena. Such calculations are based on single-particle levels extrapolated from stability, which need to be questioned given the dramatic changes in shell structure which are being uncovered recently. The plan is to measure single-particle orbitals using transfer in the A~100 region to tie down calculations in that region and to make extrapolations to the more exotic systems more reliable. The experiments will use reactions involving the transfer of single particles in collisions initiated with radioactive beams. These will be supplied by the CARIBU facility at Argonne National Laboratory which performs isotopic selection of fission fragments using a method largely independent of chemical effects and accelerates them to the required energies. The chemical independency is important as it allows beams of refractory elements to be produced. This is a unique feature which is essential for studying the A~100, Sr-Zr-Mo region. The experiments will also employ another unique device, the novel HELIOS spectrometer. This is a new concept in spectrometer design which uses a superconducting solenoid to analyse ejectile ions from transfer reactions initiated with heavy beams on light targets. It has considerable advantages over traditional methods in terms of acceptance, energy resolution and ease of particle identification. The proposal requests funds to build an essential part of this spectrometer, a device to detect the heavy recoiling ions.

理解原子核结构的一个基本方法是考虑其组成粒子、质子和中子在它们之间相互作用的影响下的运动。除了最轻的原子核之外，这些所谓的从头计算都很困难，因为随着成分数量的增加，复杂性也随之增加。当包括校正或残余相互作用时，考虑所有其他粒子产生的平均场中单个粒子运动的方法在接近稳定的原子核中取得了一些成功。这种成功实际上是相当有限的，因为与束缚同位素的总数相比，稳定系统的数量非常少，但尽管如此，这种方法甚至在学生教科书中也经常出现，给理论带来了持久性和可靠性。然而，随着实验的复杂性不断提高，人们发现了新的效应，只有在研究大范围的中子过量范围内的单粒子结构时，这些效应才会变得明显。在这些模型的背景下，单粒子结构的这种变化是令人惊讶的。例如，在某些情况下，它们甚至会扰乱稳定系统导出的“众所周知的”幻数序列。但它们也产生了更深层次的后果，因为核的潜在单粒子性质极大地影响了其他属性，例如核形状以及其他激发模式的存在和类型，例如整个核的集体振动和旋转。该拨款提案旨在研究单粒子结构的两个方面。首先调查可能导致所发现的变化的机制。这些可以直接与两个核子之间的力相关。有人认为，其中一些变化是由于该力的张量分量造成的。如果得到证实，这一点就特别有趣，因为该成分在核结构中只有少数直接表现形式。其次，该提案的目的是探测一个奇异核区域，其中基于单粒子结构的计算从稳定系统中相当粗略地推断出，预测了一些有趣的新现象。这种计算是基于从稳定性推断的单粒子水平，考虑到最近发现的壳结构的巨大变化，这一点需要受到质疑。该计划是使用 A~100 区域中的转移来测量单粒子轨道，以限制该区域的计算并使对更奇异系统的外推更加可靠。实验将使用涉及放射性束引发的碰撞中单个粒子转移的反应。这些将由阿贡国家实验室的 CARIBU 设施提供，该设施使用很大程度上独立于化学效应的方法对裂变碎片进行同位素选择，并将其加速到所需的能量。化学独立性很重要，因为它允许生产耐火元件束。这是一个独特的特征，对于研究 A~100、Sr-Zr-Mo 区域至关重要。实验还将采用另一种独特的设备，即新型 HELIOS 光谱仪。这是光谱仪设计中的一个新概念，它使用超导螺线管来分析由重光束在轻目标上引发的转移反应产生的喷射离子。它在接受度、能量分辨率和粒子识别的简易性方面比传统方法具有相当大的优势。该提案要求资金建造该光谱仪的一个重要部分，即检测重反冲离子的装置。