基于HIRFL-CSR测量丰中子重核质量的建议

A Proposal for Mass Measurements of Heavy Neutron-rich Ions at HIRFL-CSR

丰中子重核区有大量原子核质量未知,迫切需要实验测量。我们建议,利用兰州重离子加速器研究装置HIRFL-CSR上的等时性质谱术,高精度测量204Pt等丰中子重核的质量。CSR质量测量实验中,在目标核产额尽可能高的前提下,需要每次注入都有多个离子同时储存到实验环CSRe中,才能针对逐次注入修正磁场晃动的影响,得到高精度测量结果。但在丰中子核区,当目标核产生截面非常低时,每次注入能储存到环中的离子数目太少。为了解决这个问题,我们提出了一种"混合厚度靶"的方法,在不明显改变目标核产额的情况下,显著增加同时储存在CSRe中的离子数,满足实验要求。模拟计算表明,在CSRe测量丰中子重核质量是可行的,并推荐了实验的设置。

There are a large number of nuclides with unknown mass in heavy neutron-rich region, which urgently need to be measured. We propose to measure the mass of 204 Pt and other heavy neutron-rich nuclides by using the isochronous mass spectrometry(IMS) at the research facility HIRFL-CSR. In the IMS experiments, the nuclides of interest are produced by using projectile fragmentation and stored in the storage ring CSRe. The revolution times of the stored ions are measured, from which the nuclear masses are extracted. To obtain high-precision results from the IMS experiments, it is required that several ions are stored in the Experimental Cooling Storage Ring(CSRe)simultaneously to correct for the effect of the magnetic-field instability. However, the production cross sections of the heavy neutron-rich nuclides are very small, so that the number of ions that can be stored in the CSRe is too low to fulfill the requirement. To solve this problem, it is proposed to use a production target with two different thicknesses at different areas. In this way, a sufficiently large number of ions can be produced and stored in the CSRe at the same time without reducing the yield of the target nucleus significantly. The simulations show that it is feasible to measure the masses of heavy neutron-rich nuclides at CSRe. The experimental settings are recommended.