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

Abstract

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.