Effects of large mass transfer and statistical decay on ternary breakup in the reaction ${}^{238}\mathrm{U}+{}^{197}\mathrm{Au}$ at $15A$ MeV

The ternary breakup mechanism of ${}^{238}\mathrm{U}+{}^{197}\mathrm{Au}$ at $15A$ MeV has been investigated by a hybrid model that combines the improved quantum molecular dynamics (ImQMD) model together with a statistical code gemini++. The results are in good agreement with the experimental data and indicate that in peripheral reactions, ternary breakup in this reaction results from quasi-U statistical fission while for central and semicentral collisions it can be understood by a two-step mechanism: deep-inelastic collision (DIC) followed by a sequential binary breakup of one of the DIC products. In the process of DIC, there is a large mass transfer from Au to U to form transuranium. Due to the low fission barrier, such transuranium nuclei will decay into stable light nuclei through various fission modes. An event-by-event analysis shows that the second breakup mainly occurs in the deexcitation process and most of the ternary breakup events are from semicentral and peripheral collisions that correspond to deep inelastic and quasi-elastic reactions, respectively.

Figure 1

Cross sections of fragment multiplicity $M=2$ to 5 of ${}^{238}\mathrm{U}+{}^{197}\mathrm{Au}$ at $15A$ MeV. The results of both the ImQMD model (triangles) and hybrid model (circles) are given. The experimental data (open squares) are extracted from Ref. [23].

Figure 2

Binary (squares), ternary (circles), quaternary (triangles), and quinary (stars) breakup probabilities as a function of the impact parameter calculated by both the ImQMD model (open symbols) and the hybrid model (solid symbols).

Figure 3

Two-dimensional contour plots showing the differential cross section $d^2\sigma /d\text{TKE}d\text{A}$ obtained for the “ImQMD binary events.” Panels (a)–(e) are the results in five typical regions.

Figure 4

The same as in Fig. 3, but for the “ImQMD ternary events.” The results in the region $b=12–13$ fm are neglected (see text).

Figure 5

The same as in Fig. 3, but for the “Hybrid ternary events.”

Figure 6

Total kinetic energy spectrum of the “ImQMD ternary events” (short dotted lines) and the “Hybrid ternary events” (solid lines). The experimental results (short dashed lines) are taken from Ref. [23].

Figure 7

(a) Mass and (b) charge distributions of the PLFs (squares) and TLFs (circles) of the first breakup reconstructed from the “ImQMD ternary events” (open symbols) and “Hybrid ternary events” (solid symbols).

Figure 8

The mean values of the (a) mass, (b) charge, and (c) excitation energy per nucleon of the “ImQMD binary events” with respect to the impact parameter. The binary breakup products are labeled by fissioning nucleus (squares) and nonfissioning nucleus (circles).

Figure 9

The charge distributions of the fissioning and nonfissioning products. The experimental data are extracted from Ref. [23].

Figure 10

Mass distributions of the “ImQMD ternary events” (dotted lines) and the final “Hybrid ternary events” (solid lines). The three fragments are (a) the lightest fragment F3, (b) the intermediate fragment F2, and (c) the heaviest fragment F1.