Electron-capture-delayed fission properties of 234Am.

Abstract

Delayed fission following the electron-capture decay of $^{234}\mathrm{Am}$ was studied. The $^{237}\mathrm{Np}$(\ensuremath{\alpha},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\ifmmode\pm\else\textpm\fi{}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\ifmmode\pm\else\textpm\fi{}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\ifmmode\pm\else\textpm\fi{}1.3 \ensuremath{\mu}b by measuring the intensities of the daughter plutonium K x rays in radiochemically separated americium samples. The branching ratio of the 6.46-MeV \ensuremath{\alpha} peak of $^{234}\mathrm{Am}$ was found to be (3.9\ifmmode\pm\else\textpm\fi{}1.2)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ in on-line measurements. The delayed-fission probability was determined to be (6.6\ifmmode\pm\else\textpm\fi{}1.8)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$ 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.