Optimal reaction for synthesis of superheavy element 117

Fusion reactions leading to the formation of superheavy element 117 are systematically analyzed. Among the reactions considered, the 250Bk(48Ca,4n)294117 reaction has the largest evaporation residue (ER) cross section of about 2 pb. However, this reaction is hard to realize experimentally because it is difficult to accumulate sufficient amount of target material due to the short lifetime of 250Bk nucleus. For the reaction 48Ca+249Bk, our estimation shows that the ER cross sections in 3n and 4n channels may be expected to be greater than 1 pb. Therefore, 48Ca and 249Bk should be the optimal projectile-target combination for synthesis of superheavy element 117 in practice. In addition, as a main result of systematic analysis, we find that the ER cross section exponentially depends on the mass difference (in unit of temperature) of fission and neutron emission saddle points. Therefore, it is of essential importance for the successful synthesis of superheavy nuclei to select the isotopic composition of projectile and/or target so as the mass difference of fission and neutron emission saddle points as large as possible. Entrance channel effects are examined by means of a comparison of the reactions 48Ca+245Bk, 50Ti+243Am, and 55Mn+238U leading to the same compound nucleus 293117. The ER cross sections of the reactions 50Ti+243Am and 55Mn+238U are much smaller than that of 48Ca+245Bk.