Fusion vs fission in em12/11/2023 ![]() The evaporation residue cross section can be expressed as ,įor the low-energy heavy-ion collision, the capture cross section from the sub-barrier region to above the Coulomb barrier is an important issue for theoretical and experimental studies. Finally, a very small evaporation residue cross section is obtained for the superheavy nuclei production. The last stage is where the excited compound nucleus cools down through emitting neutrons or fission, and this can be evaluated by the survival probability. The second stage is that the dinuclear system evolves from the touching configuration to the formation of the compound nucleus, which can be evaluated by the fusion probability. The first stage is the capture process, which can be evaluated by the capture cross section. A schematic diagram for this process is shown in Figure 1. Theoretically, the synthesis process of superheavy nuclei can be divided into three stages. Theoretical Description of Fusion Reactions Therefore, it is important to distinguish the fusion and quasifission fragments for a better understanding of the fusion mechanism. The experimental characteristics of the quasifission process are different from the fusion-fission process. Įxperimentally, the measurement of fusion probability is required to distinguish quasifission between fusion-fission and fast fission. ![]() Some laboratories have also attempted to synthesize the Z = 119 and 120 superheavy elements by using hot fusion. Recently, the isospin effect of the target nucleus on the evaporation residue cross section has been explored. To search for the optimal condition of the superheavy nuclei production, various experiments have been performed to study the entrance channel effect on the evaporation residual cross section. Experiments based on hot fusion for synthesizing Z = 112 and 114–117 superheavy nuclei have been verified by other laboratories. From the measurement of evaporation residue cross sections, we found that there was no significant difference from Z = 112–118, and the values of the evaporation residual cross sections were all in the order of picobarn. The 48Ca-induced hot-fusion reactions were used to synthesize Z = 112−118 superheavy nuclei in experiment. Experiments of producing superheavy nuclei by cold fusion have been repeated and verified by other laboratories. Moreover, the final evaporated residual nuclei were extremely neutron deficient. The measurement of the evaporation residue cross section decreased dramatically from Z = 107 to Z = 113. The excitation energy range of the formed compound nucleus was 10–18 MeV. ![]() The superheavy elements Z = 107−112 was first synthesized by using the cold fusion reactions. Up until now, based on the fusion-evaporation reaction, the superheavy nuclei with charge numbers in the range of Z = 104118 have been synthesized successfully. However, the location of the “island of stability” has not been determined by experiment. The experimental trends α decay half-lives, and the evaporation residue cross sections of the superheavy nuclei show that the stability of superheavy nuclei increases as the neutron number approaches the closed neutron shell closure N = 184. Over the past 30 years, great progress has been achieved for superheavy nuclei production in experimental studies. Producing superheavy nuclei in the laboratory is one of the major motivations of low-energy heavy-ion physics. ![]() The predictions of the possible way to synthesize the new superheavy elements Z = 119 and 120 have also been carried out. To search for the optimal condition of synthesis, the influence of the entrance channel and the isospin of heavy colliding nuclei on the evaporation residual cross section have been studied systematically in many works. The extended nuclear landscape allows us to investigate the nuclear structure of superheavy nuclei and the nuclear reaction mechanism. On the other hand, in order to produce the new superheavy elements, or isotopes of superheavy elements, the favorable incident energy and the best combination of projectile and target should be evaluated. ![]() However, none of them has absolute advantage. Different approaches are devoted to calculate and analyze the fusion probability and the distribution of quasifission fragments. On one hand, the synthesis mechanism of superheavy nuclei needs to be elucidated. Many theoretical models have been developed to explain the experimental data. The production process of superheavy nuclei is a very complicated dynamical problem. However, results of the self-consistent models showed that the closed shell of Z = 114 becomes weaker, and Z = 114 is replaced by Z = 120 or 126. The macroscopic-microscopic models predicted 298Fl to be the double magic nucleus. Pioneer studies have theoretically predicted the “island of stability” of superheavy nuclei (SHN). The maximum mass and charge of a nucleus is a long-standing fundamental problem in nuclear physics. ![]()
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