Preparation and half-life measurement of samarium-146

Samarium-146 (an alpha emitter with a particle energy of 2.455 MeV, and currently adopted half-life of 1.03 x 108 y) is known as an extinct nuclide in the present solar system. It is expected that if 146Sm were produced in supernovae occurred in the vicinity of the solar system within the last few hundred million years, it might be present in the deep-sea sediment or ferromanganese crust as a result of cosmic fall-out from supernovae. It is, however, identified that the half-life values of 146Sm reported between 1953 and 1966 were largely scattered from 5 x 107 y to 1.03 x 108 y. Additionally, some problems are also found in the previous works. For example, poor energy resolution of a detector in alpha spectrometry and uncertainty in mass spectrometry are considered as the problems. For detailed discussion for cosmochemistry of 146Sm, the half-life of 146Sm needs to be reevaluated as well as its search on the Earth. In this work, 146Sm was produced by methods different from the previous ones to determine its half-life using modern techniques. (orig.)