Investigation of low-lying isovector octupole excitations in spherical nuclei

球形核中低位等矢量八极激发的研究

• 批准号: 230773711
• 负责人: Professor Dr. Thorsten Kröll
• 金额: --
• 依托单位: Institut für Kernphysik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2013
• 资助国家: 德国
• 起止时间: 2012-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/230773711?language=en
• 关键词: Investigation; low; lying; isovector; octupole

Aim of the project is to conduct experiments with neutron-induced reactions to determine the spectroscopic properties of recently proposed first candidates for low-lying isovector octupole excitations in spherical nuclei. Due to historical reasons the analogue low-lying isovector excitations in the quadrupole sector are commonly referred to as mixed-symmetry states. For a firm assignment of the nature of the states proposed as candidates, it is mandatory to determine the B(M1) value of the transition connecting the candidate with the first excited 3- state, the isoscalar octupole phonon, with a high level of accuracy. Therefore, it is necessary to measure for this transition the multipole mixing ratio, the relative intensity and the radiation character which has been done already in the project with the EXILL spectrometer. In addition, for the absolute B(M1) value the lifetime is needed which will be measured with the GAMS spectrometer at ILL as it is suited best for the expected lifetime in the femtosecond range. Establishing this new kind of low-lying collective mode in spherical nuclei offers several theoretical models, such as, for example, the Quasiparticle Phonon Model (QPM) or modern beyond mean-field models, the opportunity to fix the coupling constant of theisovector part of proton-neutron residual interaction in the octupole part of the multipole expansion of the effective nuclear force.

该项目的目的是进行中子诱导反应实验，以确定最近提出的球形核中低位等矢量八极激发的第一个候选者的光谱特性。由于历史原因，四极扇区中的模拟低位等矢量激励通常被称为混合对称态。为了对候选态的性质进行明确的分配，必须高精度地确定连接候选态与第一个激发三态（等标量八极声子）的跃迁的 B(M1) 值。因此，有必要测量这种转变的多极混合比、相对强度和辐射特性，这在项目中已经用 EXILL 光谱仪完成了。此外，对于绝对 B(M1) 值，需要使用 ILL 的 GAMS 光谱仪测量寿命，因为它最适合飞秒范围内的预期寿命。在球形核中建立这种新型低位集体模式提供了多种理论模型，例如准粒子声子模型（QPM）或现代超越平均场模型，有机会修复等矢量部分的耦合常数有效核力的多极扩展的八极部分中的质子-中子残余相互作用。