Unexpected isotopic trends in synthesis of superheavy nuclei

The production cross section for the heaviest nuclei in the ${}^{48}\mathrm{Ca}$ induced hot fusion-evaporation reactions is shown to depend on the isotopic composition of actinide target. It is analyzed within the dinuclear system model for compound nucleus formation. In the actinide-based reactions most neutron-rich targets available for the experiment lead to smaller cross sections. New optimal reactions for the synthesis of superheavy nuclei are suggested.

Figure 1

The maximal evaporation residue cross sections in the $3n$ channel (upper part) at the corresponding excitation energies of the compound nuclei (middle part) and $Q$ values (lower part) for the fusion reactions ${}^{48}\mathrm{Ca+}{}^A\mathrm{Th}$ (closed symbols) and ${}^A\mathrm{Ra}$ (open symbols) as functions of the mass number $A$ of the target. The experimental data of the ${}^{48}\mathrm{Ca+}{}^{232}\mathrm{Th}\to {}^{277}110+3n$ reaction [3] are presented by an open circle with error bars.

Figure 2

The same as in Fig. 1, but for the fusion reactions ${}^{48}\mathrm{Ca+}{}^A\mathrm{U}$. The experimental data of the ${}^{48}\mathrm{Ca+}{}^{238}\mathrm{U}\to {}^{283}112+3n\left(E_{CN}^{*}\approx 33\text{MeV}\right)$ reaction [3] are presented by an open circle with error bars. For the same reaction an upper limit (open triangle) of cross section was obtained in Ref. 23.

Figure 3

The same as in Fig. 1, but for the fusion reactions ${}^{48}\mathrm{Ca+}{}^A\mathrm{Pu}$. For the reaction ${}^{48}\mathrm{Ca+}{}^{244}\mathrm{Pu}$ with the same $E_{CN}^{*}$ the evaporation residue cross section in the $4n$ evaporation channel is indicated. The experimental data of the reactions ${}^{48}\mathrm{Ca+}{}^{244}\mathrm{Pu}\to {}^{288}114+4n\left(E_{CN}^{*}\approx 35–37\text{MeV}\right)$ and ${}^{48}\mathrm{Ca+}{}^{242}\mathrm{Pu}\to {}^{287}114+3n\left(E_{CN}^{*}\approx 31–33\text{MeV}\right)$ [3] are presented by open circles.

Figure 4

The same as in Fig. 1, but for the fusion reactions ${}^{48}\mathrm{Ca+}{}^A\mathrm{Cm}$. The maximal evaporation residue cross sections in the $4n$ channel (upper part) at the corresponding excitation energies of compound nuclei (middle part) are indicated. The experimental data of the reactions ${}^{48}\mathrm{Ca+}{}^{248}\mathrm{Cm}\to {}^{292}116+4n\left(E_{CN}^{*}\approx 31–36\text{MeV}\right)$ [3] are presented by an open circle.

Figure 5

The same as in Fig. 1, but for the reactions ${}^{48}\mathrm{Ca+}{}^A\mathrm{Cf}$.

Figure 6

The comparison of isotopic dependences of neutron separation energy (upper part), fission barrier of cold nucleus (middle part), and mass excess (lower part) predicted in Ref. 24 (solid squares) and Ref. 17 (open squares) for the nucleus with $Z_0=114$.

Figure 7

The same as in Fig. 6, but for the nucleus with $Z_0=118$.

Figure 8

The maximal evaporation residue cross sections in the $3n$ channel for the fusion reactions ${}^{48}\mathrm{Ca}+{}^A\mathrm{Th},{}^A\mathrm{U}$ calculated with the predictions of Ref. 24 (closed symbols) and the predictions of Ref. 25 (open symbols).

Figure 9

The maximal evaporation residue cross sections in the $3n$ and $4n$ (indicated) channels for the fusion reactions ${}^{48}\mathrm{Ca}+{}^A\mathrm{Pu},{}^A\mathrm{Cm},$ and ${}^A\mathrm{Cf}$ calculated with the predictions of Ref. 24 (closed symbols) and the predictions of Ref. 25 (open symbols).