N=20壳附近Al同位素beta衰变的研究

The unusual properties of nuclei belonging to the so-called 'island of inversion' has attracted a lot of experimental and theoretical works, which revealed exotic phenomena such as strong deformation, mixed configuration, deformed and spheriacl shape coexistence, signaling N=20 shell closure breaking. The structure at the boarder from the 'normal' shell model region into the 'island of inversion' isotopes makes it a fertile ground for various theoretical models. The neutron-rich Al isotopes around N=20 shell closure, located in the island of inversion. So far the magnetic moment measurement performed the 34Al nucleus got the different ground state properties. A large admixture of intruder states has been deduced in order to obtain a better agreement between the expermental g-factor values and the SPDF-M shell model prediction for the 34Al. Information on the 35Al excited states is missing. Shell model calculations only predict for the 36Al ground state a value I=4-. Thus more experimental inputs are threrfore needed.Now only beta-decay studies have been done at 35,36Al. In the present research, we plan to study the beta decay of neutron-rich nucleus, such as 34-36Mg and Al, at the continuous beam mode. The energies and intensities of gamma rays emitted in the beta decay of these nucleus will be measured. As results of proposed experiment, the excited states in Al isotopes will be obtained and the absolute branching ratios and Gamow-Teller strength to these excited states will be deduced. With the beta-gamma(E,t) method, the lifes of some excited states will also be measured. Comparison between the experimental data and shell model calculations could give us conclusive information on the intrinsic structure of ground state and excited states in 34-36Al. It will help us to understand the structure evolution in this mass region.

反转岛区域原子核结构的反常性质研究是放射性核束物理的一个热点，其边界区原子核内部正常sd壳成分和pf闯入态成分的激烈竞争，观察到大形变、组态混杂和形状共存等丰富的核结构现象以及N=20幻数消失的证据。因而对这些原子核的研究可以很好地检验和发展壳模型理论。N=20附近Al同位素链跨越了反转岛区域，不同实验测量得到的核结构信息相互矛盾，如有的实验认为34Al不是反转岛核，而g因子测量结果是它有更多的闯入态成分，36Al目前还有没数据，故进一步开展这方面的研究工作是很有必要的。本课题研究反转岛34-36Al的激发能级、分支比和B(GT)；同时采用beta-gamma(E,t)的方法测量34-36Al核中部分长寿命激发态的寿命，结合壳模型的理论分析，得到34-36Al是核基态和激发态确切的内部结构信息，研究反转岛边界区域原子核结构变化的规律。

“反转岛”区原子核结构的反常性质研究是放射性核束物理的一个热点，在其边界区由于原子核内部正常sd壳成分和pf闯入态成分的激烈竞争，人们观察到大形变、形状共存和组态混杂等丰富的核结构现象以及N=20幻数消失的证据，对这些原子核结构的研究可以很好地检验和发展壳模型理论。本课题通过研究“反转岛”区边界核34Al的基态和1+的isomer态的beta衰变半衰期、分支比和B(GT)值，结合壳模型的理论分析，得到34Al核的基态和激发态确切的内部结构信息。通过分析β-γ-γ符合谱以及与γ符合的β时间谱，观察到34Al衰变子核34Si中一条激发能4519keV的2+能级，讨论了34Si中建立在激发态上的γ不稳定结构存在的可能性。基于新的半衰期实验结果，系统研究了“反转岛”区N = 19 ∼ 22四条同中子素链的半衰期的变化规律。