Zeptosecond contact times for element Z=120 synthesis

The synthesis of new superheavy elements beyond oganesson (Z=118) requires fusion reactions with projectile nuclei with proton numbers larger than that of Ca-48 (Z=20), which has been successfully employed for the synthesis of elements with Z=112-118. In such reactions, fusion is drastically hindered by fast non-equilibrated dynamical processes. Attempts to produce nuclei with Z=120 using the Ni-64+U-238, Fe-58+Pu-244, Cr-54+Cm-248, and Ti-50+Cf-249 reactions have been made, which all result in larger Coulomb forces than for Ca-48-induced reactions, but no discovery has been confirmed to date. In this work, mass and angle distributions of fission fragments from these reactions have been measured with large angular coverage to aid in selection of the most promising projectile-target combination that would favorfusion. The results yield information on reaction contact times, with the longest exhibited by Ti-50+Cf-249. (C) 2020 The Authors. Published by Elsevier B.V.