Rules of thumb for synthesizing superheavy elements

Abstract

Synthesizing any elements in the eighth period using either cold or hot fusion reactions remains a big challenge to date. The quasifission mechanism restricts complete fusion to an indeterminably low evaporation residue (ER) cross-section for superheavy nuclei. The entrance channel parameters of the heavy-ion reaction, the fission barrier of the compound nucleus, the deformation parameters of the projectile and target nuclei, and the kinetic energy of the projectile are mainly responsible for governing the scale of the quasifission. The role of these factors has been examined explicitly by the experimental ER cross-sections. Thorough comparisons lead us to infer that the entrance channel criteria contribute to a much lower extent than the deformation parameters do. The effect of deformation can be categorized into four rules as validated by all the reactions used except one Uue. The null result from this reaction is explained by the improper choice of the projectile energy, as shown theoretically by means of a statistical model approach, which is valid for a system having a large nucleon number so as to intrinsically have a high density of excited states. The optimal selection of the beam energy sets another rule. Therefore, these five rules can be treated as the rules of thumb for synthesizing the superheavy elements. Application of the first four rules can enable us primarily to spot a suitable reaction, and finally, exploitation of the fifth rule chooses the most appropriate reaction at a preferable excited energy to achieve the highest ER cross-section for a superheavy element.