N=126附近Th同位素的高精度质量和无本底α衰变测量

重核的质量和α衰变测量是核物理研究的前沿和热点。受产生截面小、寿命短、反冲能低等因素的限制，质子数Z≥90、中子数N<126区域内的核素的质量从未被直接测量过，并且，在Z>82、N<126核区内，多个相邻同位素的α衰变能相近，其差别小于探测器的分辨能力，很难通过传统方法精确测量，现有数据存在较大的争议。本项目将在兰州充气谱仪SHANS上利用多反射飞行时间质谱仪，首次直接测量短寿命核素211~216Th的质量，相对精度好于5E-7，并通过质量分析选择出211~214Th同位素，在无本底环境下精确地测量这些核素的α衰变性质，α衰变能精度小于10keV/c2，半衰期相对精度达到10%，从而消除现有数据的分歧。利用这些实验结果，我们将在缺中子重核区检验原子核质量公式，研究核子间的相互作用，分析N=126附近的壳演化规律。

Both mass and α-decay measurements of heavy isotopes are the frontier and hotspot of nuclear physics research. Due to low production rates, short half-lives and low recoil energies of the reaction products, masses of isotopes in the region of proton number Z≥90 and neutron number N<126 have never been measured until now. In addition, in the region of Z>82 and N<126, many neighboring isotopes could not be identified clearly by traditional techniques because their α decay energy differences are less than the resolving power of the detection system, and thus the unclear experimental data has been controversial for decades. In this proposal, the masses of short-lived isotopes 211~216Th will be measured for the first time with relative uncertainties better than 5E-7 by using a multi-reflection time-of-flight mass spectrometer in combination with the gas-filled recoil separator SHANS, and the α-decay energies with uncertainties less than 10 keV/c2 and the half-lives with relative uncertainties better than 10% for isotopes 211~214Th will be identified in a background-free environment. Thus the previous discrepancies will be eliminated by these new experimental data. Based on the experimental results, the nuclear models and/or mass formulas will be tested, the nucleon-nucleon interactions investigated, and the shell structure evolution in the vicinity of N=126 studied.