常规等时性质量测量中系统性偏差的实验研究

Experimental Study on the Systematic Deviation in the Conventional Isochronous Mass Spectrometry

基于重离子储存环建立的等时性质谱术(IMS)是测量远离稳定线核素质量的有效工具。但是,采用常规IMS测量缺中子一侧的核素质量时,发现T_(z)=-1/2和T_(z)=-1核素的质量测量结果在宽时域范围内存在系统性偏差。本工作利用CSRe直线段上的双飞行时间(TOF)探测器,同时测量了循环离子的周期和速度。利用这些实验信息,对常规IMS质量测量中出现的系统性偏差进行了研究。发现系统偏差是由于储存的离子动量分布不对称以及储存环能量转变参数γt非恒定造成的。在离线数据处理时,发现通过限制动量接收度的大小,可以消除常规IMS质量测量中的系统偏差。这一结果对采用常规IMS进行质量测量具有重要参考价值和指导意义。

Storage-ring-based isochronous mass spectrometry(IMS)is an effective tool for mass measurements of nuclei far from stability line.However,in the mass measurements of neutron-deficient nuclei with conventional IMS,systematic deviation of mass determination was observed when nuclei with T_(z)=−1/2 and T_(z)=−1 in a wide revolution time range were measured.In this work,the revolution time and velocity of stored ions were measured simultaneously by using two time-of-flight(TOF)detectors installed in a straight section of CSRe.Using these experimental information,systematic deviation in conventional IMS was investigated experimentally.The systematic deviation is found to be caused by the different asymmetric distributions of momentum of the stored ions and the non-constant storage ring energy transition parameterγt,and it can be eliminated by limiting the momentum acceptance during offline data processing.This study provides valuable reference and significant guidance for mass measurements using conventional IMS.