Towards saturation of the electron-capture delayed fission probability; The New isotopes Es and Bk

Konki, J.*; Khuyagbaatar, J.*; Uusitalo, J.*; Greenlees, P. T.*; Auranen, K.*; Badran, H.*; Block, M.*; Briselet, R.*; Cox, D. M.*; Dasgupta, M.*; Di Nitto, A.*; Dllmann, Ch. E.*; Grahn, T.*; Hauschild, K.*; Herzn, A.*; Herzberg, R.-D.*; Heberger, F. P.*; Hinde, D. J.*; Julin, R.*; Juutinen, S.*; Jger, E.*; Kindler, B.*; Leino, M.*; Lommel, B.*; Lopez-Martens, A.*; Luong, D. H.*; Mallaburn, M.*; Nishio, Katsuhisa   ; Pakarinen, J.*; Papadakis, P.*; Partanena, J.*; Peura, P.*; Rahkila, P.*; Rezynkina, K.*; Ruotsalainen, P.*; Sandzelius, M.*; Sarn, J.*; Scholey, C.*; Sorri, J.*; Stolze, S.*; Sulignano, B.*; Theisen, Ch.*; Ward, A.*; Yakushev, A.*; Yakusheva, V.*

The new neutron-deficient nuclei Es and Bk were synthesised at the gas-filled recoil separator RITU. They were identified by their radioactive decay chains starting from Es produced in the fusion-evaporation reaction Bi(S,3n)Es. Half-lives of 6(2)s and 22s were obtained for Es and Bk, respectively. Two groups of particles with energies =8.19(3) MeV and 8.09(3) MeV were unambiguously assigned to Es. Electron-capture delayed fission branches with probabilities of 0.16(6) and 0.04(2) were measured for Es and Bk, respectively. These new data show a continuation of the exponential increase of ECDF probabilities in more neutron-deficient isotopes.