On Theoretical Problems in Synthesis of Superheavy Elements

Predictions and structure studies of superheavy elements (SHE) have been made, since the establishment of the nuclear shell model[1]. Especially in the last decade, elaborate investigations have been performed of shell correction energy and thereby of a possible location of the superheavy island in the nuclear chart. Furthermore, not only about the center of the island, but also about stability properties of nearby nuclei have been being investigated, which is useful for the extension of the nuclear chart in heavy and superheavy elements[2]. On the other hand, studies of nuclear reaction mechanisms have not been developed so much, though so-called fusion-hindrance was experimentally found to exist in heavy ion fusions and inferred to be due to energy dissipation[3]. That is, there is no reliable theoretical framework which enables us to predict fusion probability of massive systems and thereby residue cross sections of SHE properly. Thus, which combination of incident ions is most promising and what incident energy is an optimum is not yet predicted theoretically. Therefore, the fusion experiments have been performed, based on systematics of data available so far[4]. Based on the reaction theory of the compound nucleus[5], residue cross sections are given as follows,