Probing nuclear dissipation with particle multiplicity in heavy-ion-induced light fissioning systems

Based on the stochastic Langevin model, we study the effects of angular momentum ($\ell$) on the multiplicities of postsaddle neutrons, protons, and $\alpha$ particles as a function of postsaddle friction strength ($\beta$) for ${}^{200}\mathrm{Pb}$ nucleus. It is shown that with increasing $\ell$ the sensitivity of these particles to $\beta$ is significantly enhanced. Moreover, we find that neutrons (charged particles) evaporated from light ${}^{200}\mathrm{Pb}$ having high $\ell$ and high excitation energy $E^{*}$ exhibit a similar (greater) sensitivity to $\beta$ as compared to the case of heavy ${}^{251}\mathrm{Es}$ having low $\ell$ and low $E^{*}$. Our findings suggest that on the experimental side, to accurately probe information of postsaddle dissipation with particle multiplicity, in particular with the multiplicity of charged particles, it is optimal to populate light fissioning systems with large angular momentum and high excitation energy.

Figure 1

Postsaddle multiplicities of neutrons (a), protons (b), and $\alpha$ particles (c) of ${}^{200}\mathrm{Pb}$ systems as a function of $\beta$ at excitation energy $E^{*}$ = 120 MeV and at critical angular momenta $\ell$ = $10\hslash$ (squares) and $50\hslash$(triangles), respectively.

Figure 2

Comparison of sensitivity of postsaddle neutrons to $\beta$ in the absence (a) and in the presence (b) of deformation effects between light system ${}^{200}\mathrm{Pb}$ (circles) at $E^{*}$ = 150 MeV and $\ell$ = $70\hslash$ and heavy system ${}^{251}\mathrm{Es}$ (triangles) at $E^{*}$ = 70 MeV and $\ell$ = $45\hslash$.

Figure 3

(a) Change in neutron, proton, and $\alpha$-particle binding energies $\Delta B$ as a function of deformation coordinate $q$ relative to the spherical binding energies for ${}^{251}\mathrm{Es}$. (b) Emission barrier ($V_c$) of protons and $\alpha$ particles of the ${}^{251}\mathrm{Es}$ system as a function of deformation coordinate $q$.

Figure 4

Comparison of sensitivity of postsaddle protons (top panel) and $\alpha$ particles (bottom panel) to the postsaddle friction strength $\beta$ in the absence [(a) and (c)] and in the presence [(b) and (d)] of deformation effects between light system ${}^{200}\mathrm{Pb}$ (circles) at $E^{*}$ = 150 MeV and $\ell$ = $70\hslash$ and heavy system ${}^{251}\mathrm{Es}$ (triangles) at $E^{*}$ = 70 MeV and $\ell$ = $45\hslash$.