Searching of Rare Events

The significance of the study on exotic properties of nuclei far from β-stability is discussed. The searching methods for rare events are reviewed. The rare events may be searched with high production quantum, high separation efficiency and high detection efficiency. The radium is radiochemically separated from natural thorium, and thin Ra sources are prepared to obtain 228Ac through 228Ra■228Ac. The 230Ra is produced via 232Th-2p reaction induced by 60 MeV/u 18O ion irradiation of natural thorium. The radium is then radiochemically separated from the mixture of thorium and reaction products and thin Ra sources are prepared to obtain 230Ac through 230Ra■230Ac. The 239Pa is produced from the reaction 232Th (p, 3n) 230Pa in the irradiation powder target of ThO2 with 35 MeV proton beams. The sources of 230Pa■230U are prepared by radiochemical method. The sources of 228Ac, 230Ac and 230U are exposed to the solid track detectors, and measured by an HPGe ?酌-ray detector. The β-delayed fission events for 228Ac, 230Ac and heavy ion 22Ne from 230U are observed. The β-delayed fission probability of 228Ac and 230Ac were found to be (5±2)×10-12 and (1.19±0.40)×10-8, respectively and the branching ratio to decay out of 230U to be B=?姿Ne/?姿?琢=(1.3±0.8)×10-14.