Synthesis of ~(250-253)No in ~(206)Pb+~(48)Ca reaction

摘要

The dynamical cluster-decay model (DCM) is used to calculate the fusion evaporation residue cross-sections σ_(xn) for x=l-4 neutron emissions in the fusion reaction ~(206)Pb+~(48)Ca→ ~(254)No~* at various incident energies. Considering the multipole deformations up to hexadecapole deformations β_(4i) and configurations with "compact" orientation angles θ_(ci) (θ_c=2~0 for ~(206)Pb), the model is shown to give a good description of the measured individual light-particle decay channels, within one parameter fitting, the neck-length ΔR. Considering ~(204,206,207,208)Pb-based reactions, the dependence of 2n-emission yields on the isotopic composition of compound nucleus (CN) is also studied within the DCM. Of the four Pb-isotopes considered, at a fixed excitation energy E~(*~)20 MeV, ΔR is largest for CN with mass number 256, followed by 255, 254 and smallest for 252, which means to suggest that neutrons emission occurs earliest for 256, then for 255, 254 and finally for 252, in complete agreement with experimental data where ~(256)No~* has the highest cross-section and ~(252)No~* the lowest with ~(255,254)No~* lying in between. This result arises due to the penetrability factor, and is related to double magicity of both target and projectile nuclei.