丰质子fp壳原子核的beta衰变实验研究

The precise measurements of the beta decay properties for the nuclei far from beta-stability line are indispensable for understanding many aspects of nuclear structure such as shell closures, deformation, shape transitions, pairing, and isospin symmetry. The Isobaric Multiplet Mass Equation(IMME) has show a remarkable agreement with the model in wide range of nuclei. As the IMME is such a basic prediction leading from isospin concept, testing the validity of the equation is clearly of fundamental importance. Recently, the validity of IMME has been tested for A = 41, 45, 49, and 53 (T =3/2) quartets and a significant deviations have been found for the A=53. However, due to lack of the experimental data, the T=3/2 quartets have not been tested for A=43,47,51. The goals of this proposal are measurements of beta decay of pf shell proton rich nuclei with Tz=-3/2 by means of beta-proton-gamma method to look for isospin analog states (IAS) in the daughter nuclei, as well as other missing branches. The observed energies of the IAS will be used to test validity of IMME in this region. The experimental beta decay strength functions will be investigated by comparison with shell model as well.

远离beta稳定线原子核衰变性质的精确测量对于理解许多重要的物理量如闭壳、形变、形状变化、对效应以及同位旋对称性是必不可少的。最近研究人员利用CSR上测量了A=41，45，49，53(Tz=-3/2)原子核的质量，检验了这个质量区IMME公式对T=3/2四重态的适用性。他们发现其他质量的实验结果与计算结果符合得很好，但A=53核与IMME的预言有着显著的偏离。当时由于缺乏IAS态的实验数据，他们没有给出IMME在A=43，47，51的T=3/2四重态的检验。本课题拟通过beta-质子-gamma方法，系统研究fp壳丰质子Tz=-3/2的beta衰变，一方面寻找子核的IAS态，完善衰变纲图，利用IAS态的能级信息进一步检验IMME 对A=43，47，51核的适用性；同时，通过实验测量得到衰变子核的激发能级以及beta衰变强度分布函数，结合理论分析，以加深我们对A～50质子滴线附近核结构的认识。

测量了“反转岛”附近十余个原子核的半衰期，研究发现半衰期在Z = 13处出现的系统性“下沉”与反转岛边界区域原子核的正常轨道和闯入态轨道的演化相关联，因此可以将其作为反转岛的北部边界的清晰的标志。通过分析β-γ-γ符合谱以及与γ符合的β时间谱，观察到子核34 Si中1193keV和3326keV之间的符合关系，并建立了一条激发能4519keV的能级,其来自于母核34Al的1+isomer的β衰变。基于新的实验结果，我们研究了“反转岛”区N =19∼22四条同中子素链的半衰期的系统性变化规律，并与壳模型计算结果进行了比较。对于34Si中新确立的2+能级，结合实验和理论计算，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，首次给出了“反转岛”核区三轴形变存在的实验证据。.对于A~50区的实验，目前通过拟合生成核的半衰期，已经得到目标核49Fe的半衰期及邻近核48Mn、47Cr和46V的半衰期与前人的结果基本是一致的。.进一步的beta缓发质子，beta缓发gamma的数据处理和物理分析还在进行中。