An electron-capture-delayed fission study of americium-232 and americium-234.

摘要

Five 232Am and 234Am electron-capture-delayed fission (ECDF) experiments were performed to investigate the nuclear structure of 232Pu and 234Pu by searching for γ-rays emitted by these isotopes preceding nuclear fission. The Am isotopes were produced by bombarding 237Np targets with 4He 2+ or 3He2+ projectiles from the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. Samples containing the Am isotopes were transported to the center of a remote detector array using a specially-designed system that automatically changed samples, facilitating multiple-day experiments.; The six-detector array containing two silicon particle detectors and four germanium γ/x-ray detectors was optimized to detect fission fragments, α-particles, and γ/x-rays being emitted from the samples. In addition, a detailed examination was undertaken to find the optimum configuration for the components of the new sample changer system. The transport of activity to the sample changer system was found to be 72 ± 10% efficient.; The spectrum of γ/x-rays coincident with 232Pu nuclear fission from three 232Am ECDF experiments showed some enhancement in counts above the γ-ray continuum for certain energy regions. The most intense of these was a γ-ray at 140.0 ± 0.5 keV. The data suggest that 16 ± 8% of 232Pu fissions are preceded by γ-ray decay from at least one level above the ground state in the shape isomer well. Because of the weakness of other possible γ-ray transitions and the absence of measuring conversion electrons, no excited states were identified in the ground state and shape isomer wells of 232Pu.; Two experiments were performed to study the ECDF from the decay of 234Am. No γ-rays were identified that could be used to determine the character of excited states in 234Pu.