Studies of nuclear structure of neutron-rich rare-earth nuclei via detemination of spin and nuclear matrix elements

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We have studied neutron-rich rare-earth nuclei around a mass number of 150 by means of beta-gamma decay spectroscopy methods. For 150Ce, a detailed decay scheme was constructed on the basis of gamma-gamma coincidence relations. It includes 18 excited levels and 54 gamma-rays, and gives more information on the level structure than that in the published data. For 149-150Pr and 149Nd, half-lives of excited levels were determined using the delayed coincidence technique. Among them, half-lives of 87- and 126-keV levels in 149Pr were first found to be 4.2(5) and 1.0(2)ns, respectively; The 110-keV level in 150Pr shows a half-life longer than 10ns, while detailed data analysis is now in progress. This level depopulates via E1 gamma-ray emission, which usually shows short half-lives; Long half-life values are not observed in the neighboring nuclei, so that the results are attractive from a view point of nuclear structure.