壳模型研究^(10)Be和^(12)Be中的转动带结构

The descriptions of rotational bands in ^(10)Be and ^(12)Be with shell-model calculations

基于WBP和YSOX两种核子-核子相互作用,用壳模型计算研究了^(10)Be和^(12)Be的激发能谱.为了解激发态的结构性质,用轨道角动量分解方法对^(10)Be和^(12)Be的激发态波函数进行了分析,预言了可能存在的转动带结构.研究了中子数N=8壳层下^(10)Be和^(12)Be中的跨壳效应与转动带之间的关系,比较了WBP和YSOX两种相互作用计算结果的异同.此外,还研究了^(10)Be和^(12)Be核的转动特性.研究结果可为今后相关实验提供有用信息.

The rotation band is an important issue in the studies of nuclear structures,which offers a good laboratory for understanding of nuclear deformation,shell evolution,and other properties.Studies of nuclear collective rotations have mainly focused on open-shell nuclei in heavy-mass regions.Traditional collective models,such as the total Routhian surface and particle-rotor models,have been widely used.In principle,the phenomenological collective models are not suitable for the descriptions of rotations of light nuclei.The shell model with configuration interactions can describe any mass-region nuclei,as long as one chooses an appropriate model space.There have been recent studies of rotational bands of light nuclei within the shell model framework.The shell model calculation has shown a powerful model for the descriptions of low-lying states and shell evolutions.On the other hand,the shell model is a useful and popular method to analyze configurations of states.Recently,the L-S decomposition has been suggested for analyzing the collective properties of nuclei with shell-model calculation.In these light nuclei around the dripline,the intruded higher single-particle orbitals often occur in the ground states and mix with the normal single-particle orbitals.And a lot of work has been done to learn the exotic properties of the neutronrich nuclei near ^(12)Be.In the case of ^(12)Be and its neighboring nuclei,it is believed that the strong configuration mixing of the intruder states and normal states leads to large deformations.And the rotational bands can build on the band-head states with large deformations.Therefore,an interesting question is whether rotational bands can exist in such light systems,and what the corresponding configurations are in the shell-model framework.In the present paper,using the WBP and YSOX interactions,we perform shell model calculations for the low-lying states of ^(10)Be and ^(12)Be,focusing on their excitation spectra.The rotational bands are constructed using the calculated B(E2)values and excitation energies.We give the rotational energy constants of these rotational bands.To further learn the properties of the states within the rotational band,we perform the L-S decomposition.The results show that the L-S decomposition can well describe the collective properties of the rotational band in ^(10)Be and ^(12)Be.In the calculations for ^(10)Be,the WBP and YSOX interactions give similar results for L decomposition in Jπ=02+rotational band.But for ^(12)Be,the WBP and YSOX interactions give different rotational intrinsic states,which show Jπ=02+for WBP and Jπ=01+for YSOX.Further discussions on shell model configurations for rotational bands are made as well.The results show that the above two rotational bands have strong intruders from the upper sd shell orbitals in the rotational states.For the ground state of ^(12)Be,the WBP and YSOX interactions give different dominant configurations,which indicate that the intruder configuration from the sd shell in YSOX calculations is stronger.We discuss the possible origins of the difference,and future experimental studies for the rotational structure in ^(12)Be should be expected.