ELECTRON-CAPTURE DELAYED FISSION PROPERTIES OF THE NEW ISOTOPE BK-238

Electron-capture delayed fission ECDF was studied in the new isotope B k-238 produced via the Am-241(75-MeV alpha, 7n)Bk-238 reaction. The ha lf-life of the fission activity was measured to be 144+/-5 seconds. Th e mass-yield distribution is predominantly asymmetric and the most pro bable preneutron emission total kinetic energy of fission is 179+/-7 M eV. The ECDF mode in Bk-238 was verified by an x-ray-fission coinciden ce experiment which indicated that the Cm-238 fission lifetime is betw een about 10(-15) and 10(-9) seconds. The isotope was assigned to Bk-2 38 through chemical separation and observation of the known 2.4-h Cm-2 38 daughter activity. No alpha branch was observed in the decay of Bk- 238. The production cross section for Bk-238 is 150+/-20 nb and the de layed fission probability is (4.8+/-2) X 10(-4).