Dynamical Cluster-decay Model (DCM) applied to 9Li+208Pb reaction

The decay mechanism of 217At⁎ formed in Li9+208Pb reaction is studied within the dynamical cluster-decay model (DCM) at various center-of-mass energies. The aim is to see the behavior of a light neutron-rich radioactive beam on a doubly-magic target nucleus for the (total) fusion cross section σfus and the individual decay channel cross sections. Experimentally, only the isotopic yield of heavy mass residues At⁎211-214 [equivalently, the light-particles (LPs) evaporation residue cross sections σxn for x=3-6 neutrons emission] are measured, with the fusion-fission (ff) component σff taken zero. For a fixed neck-length parameter ΔR, the only parameter in the DCM, we are able to fit σfus=∑x=16σxn almost exactly for 9Li on 208Pb at all Ec.m.'s. However, the observed individual decay channels (3n-6n) are very poorly fitted, with unobserved channels (1n, 2n) and σff strongly over-estimated. Different ΔR values, meaning thereby different reaction time scales, are required to fit individually both the observed and unobserved evaporation residue channels (1n-6n) and σff, but then the compound nucleus (CN) contribution σCN is very small (<1%), and the non-compound nucleus (nCN) decay cross section σnCN contributes the most towards total σfus (=σCN+σnCN). Thus, the 9Li induced reaction on doubly-magic 208Pb is more of a quasi-fission-like nCN decay, which is further analyzed in terms of the statistical CN formation probability PCN and CN survival probability Psurv. For the reaction under study, PCN<<1 and Psurv→1, in particular at above barrier energies.