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In bombardments of 206,207,208Pb with 34S and 206Pb with 36S, we identified a new spontaneously fissioning isotope 238Cf with T sf ≈ T 1 2 = 21 ± 2 ms and obtained evidence of the production of a new isotope 237Cf with T 1 2 = 2.1 ± 0.3 s . The spontaneous-fission (SF) decay mode was established for 240Cf; its SF branch was estimated to be bsf ∼ 2 × 10−2. We measured also bsf ⩽ 1.4 × 10−4 for 242Cf and estimated bsf ∼ 10−1 for 237Cf. The production cross sections of 238Cf in the 206,207,208 Pb + 34 S reactions were measured to be in the range of 0.3 to 1.1 nb. Finally, we probed the influence of the neutron excess in the N = 20 projectile 36S on cross sections of fusion-evaporation reactions occurring on lead targets.

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 209 Bi+ 40 Ar and 208 Pb+ 37 Cl 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 240 Cm was attributed to the 1n-deexcitation channel of the composite systems 249 Md and 245 Es. At the same time, the measured 240 Cm 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 209 Bi+ 40 Ar 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, αx n) channels in the cold-fusion-type reactions induced by projectiles ranging from 37 Cl to 50 Ti on targets of 203,205 Tl, 208 Pb, and 209 Bi nuclei. Appreciable EC(β + )-delayed or/and spontaneous fission effects were detected in the 209 Bi+ 40 Ar, 208 Pb+ 37 Cl, and 206 Pb+ 37 Cl reactions. The obtained data point, in particular, to the EC(β + )-delayed fission occuring in the decay chains and .