ELECTRON-CAPTURE DELAYED FISSION PROPERTIES OF NP-228

Electron-capture delayed fission was positively identified in Np-228 p roduced via the U-233(50-MeV p,6n)Np-228 reaction. The half-life of th e observed fission activity was measured to be 61.4 +/- 1.4 s. The ECD F mode was verified by an x-ray-fission coincidence experiment. Only a bout 25% of the expected x-ray-fission coincidences were detected whic h indicates that U-228 does not have a fission isomer populated by the electron capture and that the overall lifetime of the high-energy sta tes populated by the electron capture is less than about 10(-17) s. Th e fission activity was assigned to ECDF of Np-228 based on chemical se paration and observation of known progeny activities. The ratio of ele ctron capture to alpha decay is 1.5 +/- 0.4 for Np-228. The production cross section for Np-228 is 35 +/- 10 mu b and the delayed fission pr obability is (2.0 +/- 0.9) x 10(-4). The kinetic energies of coinciden t fission fragments were measured and a preneutron emission, most prob able total kinetic energy, of 169 +/- 6 MeV was obtained. The mass-yie ld distribution was found to be predominantly asymmetric.