Electron-capture delayed fission properties of neutron-deficient einsteinium nuclei

Electron-capture delayed fission (ECDF) properties of neutron-deficient einsteinium isotopes were investigated using a combination of chemical separations and on-line radiation detection methods. 242Es was produced via the 233U(14N,5n)242 Es reaction at a beam energy of 87 MeV (on target) in the lab system, and was found to decay with a half-life of 11 ± 3 seconds. The ECDF of 242Es showed a highly asymmetric mass distribution with an average pre-neutron emission total kinetic energy (TKE) of 183 ± 18 MeV. The probability of delayed fission (PDF) was measured to be 0.006 ± 0.002. In conjunction with this experiment, the excitation functions of the 233U(14N,xn)247-xEs and 233U(15N,xn)248-xEs reactions were measured for 243Es, 244Es and 245Es at projectile energies between 80 MeV and 100 MeV.; The ECDF of 244Es, produced via the 237Np( 12C,5n)244Es reaction at an energy of 81 MeV (on target) in the lab system, was also observed to have a highly asymmetric mass distribution with an average pre-neutron emission TKE of 186 ± 19 MeV. The PDF was determined to be (1.2 ± 0.4) × 10−4. The average TKE values measured for 242Es and 244Es follow the trend observed in other ECDF systems where the TKE values are lower than for spontaneous fission.; 246Es and 248Es were both produced via the 249Cf(p,xn)250-xEs reaction at energies of 37 MeV and 18 MeV, respectively. Not enough fission events were recorded to determine the fission properties of these nuclides, but their PDF values were measured to be (3.7 ± 3.7) × 10−5 and (3.5 ± 1.8) × 10−6 for 246Es and 248Es, respectively. The P_DF values for all four einsteiniurn isotopes show the same trend of exponentially increasing P_DF with increasing electron-capture Q-value as previously observed.; The excitation function for the 249Cf(p,xn)250-x Es reaction was also studied at several different energies. The production cross sections of 245Es, 246Es, 247Es, 248Es and 249Es were measured at proton energies between 21 MeV and 40 MeV and were consistent with previously reported values.