The Preparation And Purification Of Radioactive Beam For Mass Measurement Experiments At CSRe

Mass is one of the fundamental properties of atomic nuclei.Nuclear masses are used in many research fields such as nuclear structure and astrophysics.The isochronous mass spectrometry(IMS)is a powerful tool for measuring mass measurements of short-lived nuclides.In IMS mass measurement experiments at the research facility HIRFL-CSR,nuclides of interest are produced by projectile fragmentation,selected and transported through the beamline RIBLL2,and then injected into the storage ring CSRe for mass measurements.To correct for the effect of the magnetic-field instability of CSRe,we developed a correction method which requires that several ions are stored in the CSRe simultaneously.On the other hand,the number of ions stored in the CSRe should not be too high,that would worsen the performance of the time-of-flight(TOF)detector.In the ideal case,10 to 20 ions are stored in the CSRe at the same time.This dissertation studies two problems related to the preparation and purification of the radioactive ion beams for IMS experiments at CSR.1: There are a large number of nuclides with mass unknown in heavy neutron-rich region because it is difficult to produce these nuclides in the laboratory.We designed an experimental scheme to measure the mass of 202 Ir and other heavy neutron-rich nuclides by using IMS at HIRFL-CSR.Because the production cross sections for the nuclides of interest and neighboring nuclides are very low,the ions stored in the CSRe from one injection are too few in the standard experimental settings.To solve this problem,it is proposed to use a production target with two different thicknesses at different areas.In this way,the nuclides with higher production cross section can also be stored in the CSRe,increasing the number of ions stored in the CSRe significantly without sacrificing the yield of the nuclides of interest too much.The experimental settings are recommended with the help of LISE++ simulation.2: In mass measurements experiment at CSRe,the nuclides of interest are produced with a huge amount of contamination nuclides.These nuclides are not useful for mass measurements and aggravating the performance of the TOF detector.A method based on the differences of the ions' velocities was developed for purifying the secondary beams,which was realized by adjusting the starting time of the Kicker system for injection into CSRe.To use such method,it is crucial to know the time structure of the beam pulse that is extracted fast from the CSRm.In this dissertation,the time structure of secondary beams when they are injected into CSRe is studied by analyzing the experimental data with 58 Ni as the primary beam.The limitations of this method are also discussed.