Probing nuclear dissipation with first-chance fission probability

Using the stochastic Langevin model, we investigate the influence of dissipation on first-chance fission properties of nuclei ${}^{220}\mathrm{Th}$ and ${}^{240}\mathrm{Cf}$ by calculating the drop of their first-chance fission probability caused by friction over their standard statistical-model value, $P_{f0}^{\mathrm{drop}}$, as a function of the presaddle friction strength ($\beta$) at different angular momenta and excitation energies. It is shown that the first-chance fission probability may be affected more largely at low angular momentum and that it is sensitive to $\beta$ and the sensitivity is significantly larger than that of the total fission probability. Furthermore, we find that for heavy ${}^{240}\mathrm{Cf}$, while the total fission probability is insensitive to $\beta$, the first-chance fission probability depends sensitively on $\beta$. Our findings suggest that, to more stringently constrain the presaddle friction strength, the measurement of the first-chance fission probability from those heavy fissioning systems could provide a more sensitive and suitable experimental approach.

Figure 1

Dynamical drop of the first-chance fission probability (denoted by $P_{f0}^{\mathrm{drop}}$) and of the total fission probability (denoted by $P_f^{\mathrm{drop}}$) for nucleus ${}^{220}\mathrm{Th}$ relative to that predicted by SMs as a function of the presaddle dissipation strength $\beta$ at excitation energy $E^{*}=50$ MeV and at two critical angular momenta ${\ell }_c=10\hslash$ (circles connected with red lines) and $40\hslash$ (triangles connected with blue lines).

Figure 2

Same as in Fig. 1 but at excitation energy $E^{*}=80$ MeV.

Figure 3

Calculated $P_{f0}^{\mathrm{drop}}$ and $P_f^{\mathrm{drop}}$ of heavier nucleus ${}^{240}\mathrm{Cf}$ as a function of $\beta$ at $E^{*}=50$ MeV and at ${\ell }_c=10\hslash$ and $40\hslash$. The meaning of symbols is the same as that in Fig. 1.

Figure 4

Same as in Fig. 3 but at excitation energy $E^{*}=80$ MeV.