Development of High-Efficiency Recoil Separators and Study of Rare Events in Nuclear Decay and Reaction

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The aim of the present project is to develop an isotope separator on-line (ISOL) suitable for the study of unknown short-lived nuclides far from the stability line and to prove its usufulness in actual experiments. The researches described below have been done in connection with this, resulting in the important discovery of a new effect of an ion-guide based ISOL (IGISOL), great improvement of the existing separators in INS and realization of a new type ISOL unique in the world. By using those newly developed techniques, we have sucessfully performed several experiments on the search for unknown heavy isotopes and rare phenomena in nuclear decays and reactions.1. Development of a Recoil-Type Isotope Separator (i) Discovery of a plasma effect in IGISOL. (ii) Improvement of a gas-filled recoil isotope separator (GARIS). (iii) Test and Construction of a tandem-type recoil separator, in which GARIS is used as an injector to IGISOL in order to avoid serious plasma effect in heavy-ion reactions.2. Study of Rare Phenomena (i) Identification of some neutron-deficient actinide isotopes and precise measurements on their decays. (ii) The first measurement on branching ratios of isomeric transitions in ^<211m>Po and ^<212m>Po. (iii) Measurements of capture -rays in the ^<12>C+^<12>C reaction and study of submolecular systems.