The cross sections of fusion-evaporation reactions: the most promising route to superheavy elements beyond Z=118

Abstract

Abstract. The synthesis of superheavy elements beyond oganesson (Og), which has atomic number Z = 118, is currently one of the main topics in nuclear physics. An absence of sufficient amounts of target material with atomic numbers heavier than californium (Z = 98) forces the use of projectiles heavier than 48 Ca (Z = 20), which has been successfully used for the discoveries of elements with Z = 114 − 118 in complete fusion reactions. Experimental cross sections of 48 Ca with actinide targets behave very differently to "cold" and "hot" fusion-evaporation reactions, where doubly-magic lead and deformed actinides are used as targets, respectively. The known cross sections of these reactions have been analysed compared to calculated fission barriers. It has been suggested that observed discrepancies between the cross sections of 48 Ca-induced and other fusionevaporation reactions originate from the shell structure of the compound nucleus, which lies in the island of the stability. Besides scarcely known data on other reactions involving heavier projectiles, the most promising projectile for the synthesis of the elements beyond Og seems to be 50 Ti. However, detailed studies of 50 Ti, 54 Cr, 58 Fe and 64 Ni-induced reactions are necessary to be performed in order to fully understand the complexities of superheavy element formation.

Nuclear structure dependence of fusion hindrance in heavy element synthesis

“…/V B 1 with the highest cross-section values among Ti + Pb [1,[28][29][30]. Likewise, we conclude that the 48 Ti + 204 Pb reaction has the largest QF probability. In between these cases lie the 48 Ti + 208 Pb and 50 Ti + 206 Pb reactions, which have similar widths.…”

“…For instance, almost no mass-angle correlation is apparent in either of the 50 Ti-induced reactions at below-barrier energies (corresponding to the lowest E * ), leading us to conclude that these fragments may originate from FF, with a possible contribution from slow QF. In contrast, in both of the 48 Ti reactions, relatively broad mass-angle correlations are present at all energies. Closer inspection of these broad MADs reveals, at energies close to or below V B , the presence of events close to those corresponding to projectile-and target-like fragments.…”

“…The experiment was carried out at the Heavy Ion Accelerator Facility at the Australian National University (ANU), Canberra. Beams of 48 2 MeV, respectively, by the 14UD electrostatic and the superconducting linear booster accelerators. The beams were delivered in pulses with full widths at half maximum of ≈1 ns, separated by 107 ns.…”

“…Such events are either absent or significantly reduced in the MADs of 50 Ti reactions. This may indicate that a change of 50 Ti to 48 Ti leads to a shortening of interaction times between the colliding nuclei, thus affecting the average sticking time.…”

Mechanisms Suppressing Superheavy Element Yields in Cold Fusion Reactions

“…To form even heavier elements, projectiles with more protons than 48 Ca must be used because of the near impossibility of creating enough target material of elements heavier than Cf [14]. Their use results in lower SHE yield, as demonstrated by the unsuccessful attempts to synthesize element Z ¼ 120 [15] with 50 Ti, 54 Cr [16], 58 Fe [17], and 64 Ni [18] beams. It is vital to understand the reaction dynamics in order to choose the best reactions to produce new SHE.…”