Dissipative dynamics in quasifission

Quasifission is the primary reaction mechanism that prevents the formation of superheavy elements in heavy-ion fusion experiments. Employing the time-dependent density functional theory approach, we study quasifission in the systems ${}^{40,48}\mathrm{Ca}+{}^{238}\mathrm{U}$. Results show that for ${}^{48}\mathrm{Ca}$ projectiles the quasifission is substantially reduced in comparison to the ${}^{40}\mathrm{Ca}$ case. This partly explains the success of superheavy element formation with ${}^{48}\mathrm{Ca}$ beams. For the first time, we also calculate the repartition of excitation energies of the two fragments in a dynamic microscopic theory. The differences between both systems are interpreted in terms of initial neutron to proton asymmetry of the colliding partners.

Figure 1

Quasifission in the reaction ${}^{40}\mathrm{Ca}+{}^{238}\mathrm{U}$ at $E_{\mathrm{c}.\mathrm{m}.}=209$ MeV with impact parameter $b=1.103$ fm $\left(L=20\right)$. Shown is a contour plot of the time evolution of the mass density.

Figure 2

Several observables as a function of $E_{\mathrm{c}.\mathrm{m}.}/V_B$ for ${}^{40,48}\mathrm{Ca}+{}^{238}\mathrm{U}$ central collisions with the side of ${}^{238}\mathrm{U}$. The frozen HF barrier for these configurations are $V_B=199.13$ MeV with ${}^{40}\mathrm{Ca}$ and $V_B=196.14$ MeV with ${}^{48}\mathrm{Ca}$. (a) Contact time, (b) mass and charge of the light fragment, and (c) excitation energy of the light and heavy fragments. Beyond the QF region only fusion is observed.

Figure 3

(a) Contact time and (b) mass and charge of the light fragment as a function of impact parameter.

Figure 4

TKE of both the light and heavy fragments formed in ${}^{40}\mathrm{Ca}+{}^{238}\mathrm{U}$ central collisions at $E_{\mathrm{c}.\mathrm{m}.}/V_B=1.0$–1.1. The solid line represents TKE values based on the Viola formula [51].