Technical Improvements in the Experiment of Isochronous Mass Measurement of ^(58)Ni Projectile Fragments  

作　　者：帅鹏 涂小林 张玉虎 王猛 徐星 颜鑫亮 陈相成 

机构地区：[1]Institute of Modern Physics,Chinese Academy of Sciences

出　　处：《原子核物理评论》2016年第2期173-179,共7页Nuclear Physics Review

基　　金：Natural Science Foundation of China(U1232208,U1432125,11205205,11035007,11235001,11320101004,11575007);National Basic Research Program of China(973 Program)(2013CB834401)

摘　　要：The combination of in-flight fragment separator and the isochronous mass spectrometry(IMS)in storage rings have been proven to be a powerful tool for the precision mass measurements of shortlived exotic nuclei. In IMS, the mass-over-charge ratio is only related to the revolution period of stored ions, and the relative mass resolution can reach up to the order of 10-6. However, the instability of the magnetic field of storage ring deteriorates the resolution of revolution period, making it very difficult to distinguish the ions with very close mass-over-charge ratio via their revolution periods. To improve the resolution of revolution periods, a new method of weighted shift correction(WSC) has been developed to accurately correct the influence of the magnetic field instabilities in the isochronous mass measurements of ^(58)Ni projectile fragments. By using the new method, the influence of unstable magnetic fields can be greatly reduced, and the mass resolution can be improved by a factor up to 1.7. Moreover, for the ions that still cannot be distinguished after correcting the magnetic field instabilities, we developed a new method of pulse height analysis for particle identification. By analyzing the mean pulse amplitude of each ion from the timing detector, the stored ions with close mass-over-charge ratios but different charge states such as ^(34)Ar and ^(51)Co can be identified, and thus the mass of ^(51)Co can be determined. The charge-resolved IMS may be helpful in the future experiments of isochronous mass measurement even for N = Z nuclei.The combination of in-flight fragment separator and the isochronous mass spectrometry（IMS） in storage rings have been proven to be a powerful tool for the precision mass measurements of short- lived exotic nuclei. In IMS, the mass-over-charge ratio is only related to the revolution period of stored ions, and the relative mass resolution can reach up to the order of 10-6. However, the instability of the magnetic field of storage ring deteriorates the resolution of revolution period, making it very difficult to distinguish the ions with very close mass-over-charge ratio via their revolution periods. To improve the resolution of revolution periods, a new method of weighted shift correction （WSC） has been developed to accurately correct the influence of the magnetic field instabilities in the isochronous mass measurements of 5SNi projectile fragments. By using the new method, the influence of unstable magnetic fields can be greatly reduced, and the mass resolution can be improved by a factor up to 1.7. Moreover, for the ions that still cannot be distinguished after correcting the magnetic field instabilities, we developed a new method of pulse height analysis for particle identification. By analyzing the mean pulse amplitude of each ion from the timing detector, the stored ions with close mass-over-charge ratios but different charge states such as 34Ar and 51C0 can be identified, and thus the mass of 51Co can be determined. The charge-resolved IMS may be helpful in the future experiments of isochronous mass measurement even for N - Z nuclei.

关 键 词：nuclear mass storage ring isochronous mass spectrometry mass measurement 

分 类 号：O571.6[理学—粒子物理与原子核物理] P142.9[理学—物理]