Identification of neutron-rich new isotopes and their half-lives

Recently, some new isotopes such as 156Pm, 155Nd, 154Pr, 152Ce were identified using on-line isotope separation apparatus (KUR-ISOL). The half-lives of these isotopes were several seconds and those of other unknown nuclides are assumed to be around one second or extremely shorter. Detections of 150La, 153Ce, 157Nd etc. have not been succeeded by previous studies. In order to raise the efficiency for identification of short-lived nuclides, it seems essential to remarkably increase the beam strength of KUR-ISOL and to secure its safety operating. A mixed-gas jet method has been developed using a mixed gas of N2 and He and the beam strength increased by more than one digit. In addition, the exchange over time for gas was shortened by increasing the gas flow volume. Next, various aerosols were tested to select a stable and high efficient ion source and PbI2 aerosol was chosen as the most suitable one. A 4πβ-γ-coinsidence spectrometer with plastic scintillator of 1 mm in depth was constructed and simultaneous measurement for β-ray and γ-ray as well as measurement for a single spectre became possible. Thus identification of 150La was succeeded by those improvements of KUR-ISOL and the use of 4πβ-γ-coinsidence spectrometer. (M.N.)