Electron capture decay of 238Am and electric monopole transitions in 238Pu

Abstract

Mass-separated samples of 238 Am(T 1 2 = 98 min) have been used to investigate the EC decay scheme of 238Am. The γ-ray and conversion electron spectra were measured with high-resolution Ge(Li) and Si(Li) spectrometers. Several electric monopole transitions were identified. The K/L ratios of the EO transitions are in agreement with the theoretical values of Church and Weneser. A γ-ray spectrum was measured in coincidence with the electron lines of the 44.1 keV transition in order to distinguish transitions going to the ground state from those terminating at the 2 + or 4 + member of the ground state band. From these data a decay scheme has been constructed. Assignments of levels already known from the β − decay of 2338Np and α-decay of 242Cm have been confirmed. Several other low-spin states have been postulated to account for the observed γ-rays and conversion electrons. From log ft value considerations the ground state of 238Am has been given an assignment of { n[743] 7 2 −; p[523] 5 2 −}1 + and the 962.8 keV level of 238Pu has been assigned to { n[743] 7 2 −; n[622] 5 2 +}1 − . The half-life of 238Am has been measured to be 98±3 min. A 5.94 MeV α-group has been assigned to 238Am decay. The α-branching has been measured to be (1.0±0.4)×10 −4%.