Isospin effect on pre-scission particle emission

The isospin effect of particle emission for fissioning isobaric sources of 212Tl, 212Po and 212Fr and for isotopic sources of 189,202,212Po are explored in the framework of the Smoluchowski equation. The multiplicity of emitted particles shows a strong dependence on the isospin of the fission sources. Similar results are also observed for light fissioning isobaric sources of 110Tc, 110Pd and 110In and for isotopic sources of 110,117,124In. This indicates that the effect of isospin on the emission of particles is independent of the size of the fissioning system. It has been found with the increase of the isospin of heavy fissioning systems, the emission of charged particles is not sensitive to the viscosity strength. In addition, an Er isotopic chain is used to study the effects of isospin on pre-scission particle emission for various mass-asymmetric fission processes with a statistical model modified to include dissipation effects in fission. Calculations show that with the increase of the isospin of the Er nucleus, neutron emission increases, while the multiplicities of protons and α particles decrease. Again, we note that when the isospin in the fissioning system reaches a certain value, light charged particle multiplicities are no longer dependent on the fission time scale, which means that for systems of very high isospin, protons and α particles cannot be employed as probes of dissipation in fission. (author)