Role of Mass Asymmetry in Fusion of Super-Heavy Nuclei

Abstract

By using well tested standard statistical model for calculating survival probabilities of super-heavy compound nuclei, Psurv, and reliably predicted capture cross sections σcap, "empirical" values of the fusion hindrance Pfus = σsyn/(σcap · Psurv) have been determined from the formation cross sections σsyn for production of super-heavy nuclei of 102 ≤ Z ≤ 113 measured at GSI Darmstadt and RIKEN. So determined fusion hindrance can be well reproduced with a simple model based on the Smoluchowski diffusion equation applied to describe thermal shape fluctuations of the fusing system. An applicability of this model for a wider class of fusing systems could be verified on data from an interesting experiment on the synthesis of isotopes of Hs (Z = 108) in the 136 Xe + 136 Xe reaction, scheduled to be carried out in Dubna this year. Synthesis cross sections for 269-271 Hs isotopes, strongly reduced by the fusion hindrance effect in this symmetric fusion reaction, are predicted.

Systematics of fusion probability in “hot” fusion reactions

“…For the fusion reactions synthesizing element 120 with projectiles 54 Cr and 58 Fe, the cross sections fall to a few femtobarns which seems beyond the limit of the available facilities. * Electronic address: tianjunlong@gmail.com 1 Synthesis of super-heavy nuclei (SHN) through fusion reactions is a field of very intense studies in the recent decades [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Up to now, the superheavy elements Z = 107 ∼ 118 have already been synthesized [1][2][3][4][5][6] through "cold" fusion reactions that use lead or bismuth targets with appropriate projectiles following the emission of one or two neutrons from a "cold" compound system, or "hot" fusion reactions that use actinide targets from uranium to californium with beams of 48 Ca following the evaporation of 3 to 5 neutrons from a "hot" system.…”

“…2 shows the fusion probability in reactions leading to SHN as a function of the quasi-fission barrier height fusion reactions with E * = 15 MeV and the extracted fusion probability in Ref. [14] for the same reactions, respectively. Here the parameter C is slightly different for the "cold" fusion reactions which will be discussed later.…”

Synthesis of superheavy elements: Uncertainty analysis to improve the predictive power of reaction models

“…The theoretical results can be found in Refs. [10,[16][17][18][19][20]. The figure is adapted from Ref.…”

“…We should be aware that this simplified version of Eq. (1) has been widely employed to estimate ER cross-sections in many recent studies [10,14,19,20] due to its simplicity. As mentioned in the introduction, we only focus on the one-neutron evaporation channel.…”

Processes in massive nuclei reactions and the way to complete fusion of reactants. What perspectives for the synthesis of heavier superheavy elements?

“…The study of the hypothetical collision between the 108 Mo and 144 Ba nuclei allows us to demonstrate why the fusion of massive reactants is not the inverse process of fission with almost symmetric fragments which are formed in the case of the 252 Cf spontaneous fission. The failure of many experiments is connected not only with the difficulties in the measurement of the evaporation residue cross sections which are lower than 0.5 pb but also in the inadequacy of estimation of the complete fusion probability [1][2][3]. The reported difficulties are related not only with the theoretical estimation of the complete fusion and evaporation residue cross section but also in the not univocal experimental identification of fusion-fission fragments among the quasifission and fast fission fragments.…”