Theoretical Predictions of Residues Cross Sections of Superheavy Elements

Dynamical reaction theories are reviewed for synthesis of superheavy elements. Characteristic features of formation and surviving are discussed with reference to possible incident channels. Theoretical predictions are presented on favorable incident channels and on optimum energies for synthesis of Z = 114. 1. Introduction Superheavy elements around Z = 114(or 126) and N = 184 have been believed to exist according to theoretical predictions of stability given by the shell correction energy in addition to average nuclear binding energy 1). This means that heavy atomic nuclei with fissility parameter x 1 could be stabilized against fission by a huge barrier which is resulted in by the additional binding of the shell correction energy around the spherical shape. In other words, if superheavy compound nuclei(C.N.) are formed in such high excitation that the closed shell structure is mostly destroyed, they have no barrier against fission and thus are inferred to decay very quickly, though time scales of fission are now believed to be much longer than that of Bohr-Wheeler formula due to a strong friction for the collective motion 2). Therefore, the point is how to reach the ground state of the superheavy nuclei, or how to make a soft-landing at them. In order to minimize fission decays of C.N. or maximize their survival probabilities, so-called cold fusion reactions have been used, which succeeded in synthesizing SHEs up to Z = 112 3). They have the merit of large survival probabilities, but suffer from the demerit of small formation probabilities because of the sub-barrier fusion. On the other hand, so-called hot(warm) fusion reactions have the merit of expected large formation probabilities and the demerit of small survival probabilities due to relatively high excitation of C.N. formed. Anyway, an optimum condition for large residue cross sections of SHEs is a balance or a compromise between formation and survival probabilities as a function of incident energy or excitation energy of C.N. formed over possible combinations of projectiles and targets 4) .