RUI: Shell Structure and Core Polarization in Exotic Nuclei

众所周知，原子核是由质子和中子组成的。正如核科学咨询委员会所确定的，核科学中的一个大问题是，随着中子数量的增加，原子核是如何组织的（根据中子和质子之间的力）。这项提议的目标是了解富含中子的原子核结构的演变，重点关注含有28个中子的同位素，如Ca-48核（也有20个质子）。众所周知，这样的原子核对放射性衰变具有不寻常的稳定性，但对于质子数减少的同位素来说，稳定性就不那么高了。这些实验涉及质子与选定原子核的碰撞，将在国家超导回旋加速器实验室（NSCL）进行。本科生将参与实验并获得数据采集、分析和模拟的实用技能，并在会议上展示他们的工作。所提出的逆运动学质子散射测量通过解开外来核中中子和质子对集体激发的贡献来探测集体和单粒子行为之间的相互作用。驱使N = 28壳在Z = 14附近侵蚀的机制是一个非常有趣的话题。有人提出，质子驱动这个区域集体的发生。中子和质子对集体激发的相对贡献的实验测定将提供重要的见解。对同位素S-44和Si-42的测量将完成中子和质子对Ca-48以下的N=28等音的前2+激发的相对贡献的经验图像，直到Z=14， N=28壳层坍塌。对同位素P-41和P-43的测量将澄清奇数质子与这些核中Si-40和Si-42“核”的集体前2+激发的耦合程度。

It is a well-known fact that nuclei are made up of protons and neutrons. One of the big questions in nuclear science, as identified by the Nuclear Science Advisory Committee, is how nuclei are organized (in terms of the forces between neutrons and protons) as the number of neutrons is increased. The goal of this proposal is to understand the evolution of the structure of neutron-rich nuclei, with a focus on isotopes with 28 neutrons, such as the nucleus Ca-48 (that also has 20 protons). Such nuclei are known to have unusual stability against radioactive decay, but become less stable for isotopes where the proton number is decreased. The experiments, which involve collisions of protons with selected nuclei, will be done at the National Superconducting Cyclotron Laboratory (NSCL). Undergraduate students will participant in the experiments and will gain practical skills in data acquisition, analysis and simulation, and present their work at conferences. The proposed inverse-kinematics proton scattering measurements probe the interplay between collective and single-particle behavior by disentangling the neutron and proton contributions to collective excitations in exotic nuclei. The mechanism(s) driving the erosion of the N = 28 shell approaching Z = 14 is a topic of great interest. It has been suggested that protons drive the onset of collectivity in this region. The experimental determination of the relative contributions of neutrons and protons to collective excitations will provide important insight. Measurements of isotopes S-44 and Si-42 will complete the empirical picture of the relative contributions of neutrons and protons to the first 2+ excitations in the N=28 isotones below Ca-48 down to Z=14, where the N=28 shell collapses. Measurements of isotopes P-41 and P-43 will clarify the degree of coupling of the odd proton to the collective first 2+ excitations of the Si-40 and Si-42 "cores" in these nuclei.