Cross sections of the (HI, αn) channel in the cold-fusion-type reactions 209Bi+ 40Ar and 208Pb+ 37Cl

Abstract

By applying an off-line radiochemistry technique, cross sections for the production of the isotope 240 Cm(T 1 2 =27 d) in the cold-fusion-type reactions 209Bi+ 40Ar and 208Pb+ 37Cl at the bombarding energy E lab⩽230 MeV were determined to be 0.5±0.2 nb and 0.6±0.3 nb, respectively. The production of 240Cm was attributed to the 1n-deexcitation channel of the composite systems 249Md and 245Es. At the same time, the measured 240Cm production cross sections represent upper cross-section limits for the (HI, αn) channel of the reactions under study. These upper limits are about 100 times lower than the cross-section values reported recently by Nomura et al. for the ( 40 Ar, αx n) channels with x=1,2 of the 209Bi+ 40Ar reaction at E lab=208 MeV. In the context of the above measurements, presented and discussed is the up-to-date summary of the available evidence on cross sections of the (HI, αxn) channels in the cold-fusion-type reactions induced by projectiles ranging from 37Cl to 50Ti on targets of 203,205Tl, 208Pb, and 209Bi nuclei. Appreciable EC(β +)-delayed or/and spontaneous fission effects were detected in the 209Bi+ 40Ar, 208Pb+ 37Cl, and 206Pb+ 37Cl reactions. The obtained data point, in particular, to the EC(β +)-delayed fission occuring in the decay chains ▪ and ▪.