Attempts to produce new americium isotopes near N=126

Searches for new americium isotopes with neutron number around 126 are made in bombardments of Ir-191,Ir-193 targets with Ar-40 ions by employing the gas-filled recoil separator SHANS and the recoil-alpha correlation technique. No evidence for nuclides of interest is obtained, and the upper limits of the cross sections producing the evaporation residues are estimated to be 31.4 pb and 5.4 pb for the reactions of Ar-40 +Ir-193 and Ar-40 + Ir-191, respectively. We have performed microscopic finite-temperature Skyrme Hartree-Fock+ (Bardeen- Cooper-Schripffer theory) BCS calculations, and found that the fission barriers of compound nuclei in this region decrease rapidly with increasing proton number. The non-observation of new americium isotopes would be attributed to small survival probabilities of the Am-231 and Am-233 compound nuclei due to their much reduced fission barriers at high excitations.