双幻核56Ni附近价质子-中子相互作用研究

The proton-neutron interaction is essential for the development of configuration mixing and for the onset of collectivity and deformation in nuclei, for changes of the underlying shell structure, and for the microscopic origins of phase transitional behaviour in nuclei. Nuclear masses represent the sum of all the interactions in atomic nuclei. The empirical proton-neutron interactions of the valence nucleons can be extracted from nuclear masses. It has been predicted that valence proton-neutron interactions exhibit distinctive patterns around double magic nuclei due to the various overlaps of the wave functions of the last protons and neutrons. In this proposal, evolution of the proton-neutron interaction around double magic nuclide 56Ni will be investigated and the empirical predictions will be tested. For this purpose, the masses of 52Co, 56Cu will be measured for the first time by using the isochronous mass spectrometry (IMS) at HIRFL-CSR facility in Lanzhou. The primary beam of 58Ni will be used to produce the nuclei of interest, which in turn will be injected into the CSRe and stored there. The CSRe will be set as an IMS for 52Co, then the mass-to-charge ratios of the stored ions depend directly on their revolution times. The resolving power of IMS is crucial for this proposal, which demand clear separation of the ground state and an isomeric state expected at around 400 keV in 52Co. To fulfil the requirement new techniques that allow to monitor and fine tune the IMS setting in real time has to be developed. The time-of-flight detector that is used to measure the revolution times of the stored ions will be improved too. The excitation energy of the isomeric state in 52Co will be determined. By comparing this energy with that in the mirror nuclide, the nuclear isospin symmetry will be studied as well.

原子核中的质子-中子相互作用在原子核形变和集体运动的产生，壳的演化，原子核相变等方面都起了重要作用。原子核质量反映了把核子结合到一起的所有相互作用的总和。价质子-中子相互作用是原子核最外层轨道核子间的相互作用，通常由原子核的质量数据来提取。研究认为，价质子和价中子的波函数空间重叠和价质子-中子相互作用的强弱直接相关。基于这个原理预言了在双幻核附近，价质子-中子相互作用会有比较大的变化。本项目研究双幻核56Ni邻近区域的价质子-中子相互作用的演化，并检验相关理论。为此，计划在兰州大科学装置HIRFL-CSR上，使用基于CSRe的等时性质量谱仪，首次精确测量56Cu和52Co的质量。我们将通过在线监测并适时调整谱仪设置来保证对目标核的分辨能力，并改进时间探测器提高谱仪精度。通过比较52Co及其镜像核中同核异能态的激发能，我们还将检验原子核的同位旋对称性。

基于兰州大科学装置HIRFL-CSR，利用等时性质谱术首次测量了56Cu和52Co等短寿命核素的质量。通过得到的高精度质量数据，研究了双幻核56Ni邻近区域的价质子-中子相互作用的演化。原子核中的质子-中子相互作用在原子核形变和集体运动的产生、壳的演化、原子核相变等方面都起了重要作用。理论研究认为，价质子和价中子的波函数空间重叠和价质子-中子相互作用的强弱直接相关。基于这个原理预言了在双幻核附近，价质子-中子相互作用会有比较大的变化。本研究发现，在双幻核56Ni邻近区域，在价质子和价中子占据相同轨道时价质子-中子的相互作用较大，符合理论预期。CSRe利用精确测量的52Co基态和同质异能态的质量值，结合已有数据重新构建了52Ni的β衰变纲图，重新指认了52Co中T=2的同位旋相似态，发现IMME公式依然能够描述A=52、T=2的同位旋相似态，并指出了在β缓发质子谱研究中普遍使用了50年之久的同位旋相似态指认规则的局限性。