相对论多组态相互作用方法计算Mg~+离子同位素位移

采用相对论多组态相互作用方法研究了Mg~+离子3s~2S_(1/2)—3s~2P_(1/2)和3s~2S_(1/2)—3s~2P_(3/2)两条跃迁谱线的特殊质量位移系数和场位移因子,并计算了中子数8≤N≤20的Mg~+离子的同位素位移.计算结果与其他理论的计算值符合得比较好,与最新的实验测量结果比较,相对误差在0.13%到0.28%范围,是目前最接近Mg~+离子同位素位移实验测量的理论计算结果.该计算结果可为Mg~+离子同位素位移实验和理论研究提供参考,能够用于Mg~+离子的短寿命同位素的光谱测量实验以及利用Mg~+离子开展幻中子数N=8和N=20附近的奇异原子核特性研究等.所用的计算方法和电子激发模式也可以推广到其他核外电子数为11的多电子体系,用于开展相应的原子光谱结构计算和同位素位移的理论研究.

Calculationof isotope shift of Mg+ ion by using the relativistic multi-configuration interaction method

The special mass shift coefficients and field shift factors for the atomic transitions 3s²S_1/2-3s²P_1/2 and 3s²S_1/2-3s²S_3/2 of Mg⁺ ion are calculated by the relativistic multi-configuration interaction method, and the isotope shifts are also obtained for the Mg⁺ isotopes with the neutron numbers 8 ≤ N ≤ 20. Our calculations are carried out by using the GRASP2 K package together with the relativistic isotope shift computation code package RIS3. In our calculations the nuclear charge distribution is described by the two-parameter Fermi model and the field shifts are calculated by the first-order perturbation. In order to generate the active configurations, a restricted double excitation mode is used here, the electron in the 3s shell (3s¹) is chosen to be excited, another electron is excited from the 2s or 2p shells (2s²2p⁶), and the two electrons in the inner 1s shell (1s²) are not excited. The active configurations are expanded from the occupied orbitals to some active sets layer by layer, each correlation layer is labeled by the principal quantum number n and contains the corresponding orbitals s, p, d…etc. The maximum principal quantum number n is 6 and the largest orbital quantum number l_max is g. According to our calculations, the normal mass shift coefficients are -586.99 GHz·amu and -588.50 GHz·amu, the special mass shift coefficients are -371.90 GHz·amu and -371.95 GHz·amu, the field shift factors are -117.10 MHz·fm^-2 and -117.18 MHz·fm^-2 for the 3s²S_1/2-3s²P_1/2 and the 3s²S_1/2 -3s²S_3/2 transitions of Mg⁺ ions, respectively. Then the isotope shifts for different Mg⁺ isotopes are obtained using the available data of the nuclear mass and the nuclear charge radii. Our results are coincident with other theoretical calculations and also with experimental results. The relative errors of our calculations are in a range from 0.13% to 0.28% compared with the latest measurements. Our calculations are the most consistent with the experimental measurements for the moment. The results provided here in this paper could be referred to for the experimental and theoretical study of Mg⁺ isotope shift, and they could be applied to the spectral measurement experiments of the short-lived Mg⁺ isotopes and also used for the research of the characteristics of exotic nuclei with Mg⁺ isotopes near the magic neutron numbers N=8 and N=20. The calculation method and the excitation mode used here could also be extended to other multi-electron systems with eleven orbital electrons, and the corresponding theoretical studies of the atomic spectral structures and isotope shifts could then be carried out.