Delayed fission following the electron-capture decay of ${}_{}{}^{234}{}_{}{}^{}\mathrm{Am}$ was studied. The ${}_{}{}^{237}{}_{}{}^{}\mathrm{Np}$(α,7n${)}^{234}$Am reaction with multiple ${}_{}{}^{237}{}_{}{}^{}\mathrm{Np}$ targets was used to produce ${}_{}{}^{234}{}_{}{}^{}\mathrm{Am}$. The fission properties and half-life of ${}_{}{}^{234}{}_{}{}^{}\mathrm{Am}$ were measured using a rotating-wheel system. The half-life of ${}_{}{}^{234}{}_{}{}^{}\mathrm{Am}$ was determined to be 2.32±0.08 min from measurements of the fission activity. A highly asymmetric mass-yield distribution was observed for the fission activity, and the average total kinetic energy of the fission fragments was found to be 173±5 MeV. Radiochemical separations confirmed the elemental assignment of the fissioning species to americium or fission from short-lived excited states in its EC daughter, plutonium. The cross section for ${}_{}{}^{234}{}_{}{}^{}\mathrm{Am}$ produced by this reaction and decaying by electron capture was determined to be 5.4±1.3 μb by measuring the intensities of the daughter plutonium K x rays in radiochemically separated americium samples. The branching ratio of the 6.46-MeV α peak of ${}_{}{}^{234}{}_{}{}^{}\mathrm{Am}$ was found to be (3.9±1.2)×${10}^{\mathrm{-}4}$ in on-line measurements. The delayed-fission probability was determined to be (6.6±1.8)×${10}^{\mathrm{-}5}$ from the measured ratio of fissions to plutonium K x rays. The observed fissions were unambiguously assigned to an EC-delayed fission process by measuring fissions coincident with the K-capture x rays.

• Received 7 August 1989

DOI:https://doi.org/10.1103/PhysRevC.41.618