CROSS-SECTIONS OF THE (HI, ALPHA-N) CHANNEL IN THE COLD-FUSION-TYPE REACTIONS BI-209+AR-40 AND PB-208+CL-37

By applying an off-line radiochemistry technique, cross sections for the production of the isotope Cm-240 (T1/2 = 27 d) in the cold-fusion-type reactions Bi-209 + Ar-40 and Pb-208 + Cl-37 at the bombarding energy E(lab) less-than-or-equal-to 230 MeV were determined to be 0.5 +/- 0.2 nb and 0.6 +/- 0.3 nb, respectively. The production of Cm-240 was attributed to the 1n-deexcitation channel of the composite systems Md-249 and Es-245. At the same time, the measured Cm-240 production cross sections represent upper cross-section limits for the (HI, alphan) 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 (Ar-40, alphaxn) channels with x = 1,2 of the Bi-209 + Ar-40 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, alphaxn) channels in the cold-fusion-type reactions induced by projectiles ranging from Cl-37 to Ti-50 on targets of Tl-203, Tl-205, Pb-208, and Bi-209 nuclei. Appreciable EC(beta+)-delayed or/and spontaneous fission effects were detected in the Bi-209 + Ar-40, Pb-208 + Cl-37, and Pb-206 + Cl-37 reactions. The obtained data point, in particular, to the EC(beta+)-delayed fission occurring in the decay chains Es-242 [GRAPHICS] Cf-242 and Bk-238 [GRAPHICS] Cm-238.