Alpha-decay Study Of The Very Neutron-deficient Ac Isotopes And Exploration Of ER-γ-α-γ Coincidence Measurements

A gas-filled recoil separator, SHANS(Spectrometer for Heavy Atom and Nuclear Structure) at the Institute of Modern Physics in Lanzhou(IMP) is dedicated to the experimental study of superheavy nuclei. At present, synthesis of neutron-deficient isotopes around Z=92 has been performed at SHANS. This dissertation mainly contains two parts discussed as follows:Very neutron deficient actinium isotopes were produced in the complete-fusion evaporation reaction of 40 Ca +169Tm. The SHANS was employed to collect the fusion products. The recoils were implanted into Si-BOX detectors. The isotopes were identified using position-time correlations between the implants and the decays. An unknown α-decaying state, with Eα=7.935(30)Me V and211/2 4T11 ms+-=, was assigned to the new isotope 205 Ac. The observed α decay has been determined to originate from the ground-state of 205 Ac with the configuration of-2/9)(2/9nph based on the systematic analysis of the reduced α-decay width(d2).The decays of 214,215 Th,214,215 Ac å'Œ 210,212 Ra isotopes with neutron number close to N=126 were investigated by ER-g-α-g coincidence measurements. The nuclei were produced by the reaction 40Ca+nat Hf. Evaporation residues recoiling out of the target were separated in flight by SHANS and stopped in Si-BOX detectors in order to study their subsequent decays. Correlated g rays were detected by a Clover Germanium detector. In the present work, decay schemes have been extracted for the isomers and the ground states of isotopes mentioned above. The results were discussed andcompared to the previously published data. The experimental observation is in good agreement with the known data. The method established in the presented work would be very useful for the future experimental study at SHANS.