Towards saturation of the electron-capture delayed fission probability: The new isotopes Es-240 and Bk-236

The new neutron-deficient nuclei 240Es and 236Bk were synthesised at the gas-filled recoil separator RITU. They were identified by their radioactive decay chains starting from 240Es produced in the fusion–evaporation reaction 209Bi(34S,3n)240Es. Half-lives of View the MathML source6(2)s and View the MathML source22−6+13s were obtained for 240Es and 236Bk, respectively. Two groups of α particles with energies View the MathML sourceEα=8.19(3)MeV and View the MathML source8.09(3)MeV were unambiguously assigned to 240Es. Electron-capture delayed fission branches with probabilities of 0.16(6)0.16(6) and 0.04(2)0.04(2) were measured for 240Es and 236Bk, respectively. These new data show a continuation of the exponential increase of ECDF probabilities in more neutron-deficient isotopes. ispartof: Physics Letters B vol:764 pages:265-270 status: published