181Hg的低激发态谱学实验研究

The neutron deficient isotopes near Z=82 and between N=82 and N=126 exhibit the very extensive manifestation of shape coexistence, and have attracted much attention theoretically and experimentally. The 181Hg which is located at the critical point of a shape phase transition in the odd-Hg nuclei, was the subject of several experiments of different types in the recent years. However, experimental information concerning its level structure is still limited, especially at low excitation energies. This proposal is aimed at the measurement of decay of 13/2+ isomeric state via alpha-decay of 185Pb and isomeric decay of 181Hg, to establish the level structure of 181Hg and 185Pb at low excitation energy. The observed energies of these excited states will be used to investigate evolution of the low-energy shape coexistence in this mass region.

质子数接近Z=82，中子数位于82和126之间的原子核区呈现出极为丰富的形状共存现象，一直受到实验和理论方面的极大关注。181Hg在奇中子同位素中位于形状相变点，目前其能级结构信息尤其是低激发态的能量等信息是缺失的。对其进行进一步实验研究对于理解Hg同位素的形状共存和形状演化具有重要的意义。我们拟通过185Pb的α衰变和181Hg的isomer衰变实验分别布居181Hg的13/2+ 的isomer态，测量其衰变，最终确定181Hg和185Pb中低位态能级信息，从而分析相应组态的性质，探讨形状共存在附近核区的系统演化规律。

在兰州近代物理研究所SHANS终端通过熔合蒸发反应86W(40Ar, 1p3n)222Pa研究了222Pa的alpha衰变。通过新发展的有效脉冲叠加算法对ER(222Pa)->(222Pa)->(218Ac)衰变链的叠加信号进行了解谱，首次观测到8690 keV 的alpha分支，并将其指定为基态到基态的跃迁。由此得到222Pa的基态质量，该实验值与质量表的估计结果符合很好。FRDM模型与RMF+BCS模型的质量计算表明222Pa的基态具有八级形变。RMF+BCS的势能面计算表明222Pa的基态具有稳定的四极-八级形变。在Pa同位素中的禁戒因子的系统性表明222Pa是Pa同位素中从四极到八级形变的相变点。在本项目的支持下开展了丰中子Ag同位素，近滴线核22Al的beta衰变研究工作得到了丰中子N=82原子核结构演化以及轻核区质子衰变模式等重要的物理结果。