Survival of orbiting in ${}^{20}\mathrm{Ne}$ (7–10 MeV/nucleon) + ${}^{12}\mathrm{C}$ reactions

The inclusive energy distributions of fragments with Z $\ge$ 3 emitted from the bombardment of ${}^{12}\mathrm{C}$ by ${}^{20}\mathrm{Ne}$ beams with incident energies between 145 and 200 MeV have been measured in the angular range ${\theta }_{\mathrm{lab}}~{10}^{°}\text{−}{50}^{°}$. Damped fragment yields in all cases have been found to be characteristic of emission from fully energy equilibrated composites; for B and C fragments, average Q values, $\langle Q\rangle$, were independent of the center-of-mass emission angle (${\theta }_{\mathrm{c.m}.}$), and the angular distributions followed a $~1/\sin {\theta }_{\mathrm{c.m}.}$-like variation, signifying long lifetimes of the emitting dinuclear systems. Estimates of total yields of these fragments have been found to be much larger than those predicted by the standard statistical model. This may be indicative of the survival of an orbiting-like process in the ${}^{12}\mathrm{C}+{}^{20}\mathrm{Ne}$ system at these energies.

Figure 1

Measured energy distributions of the B and C fragments emitted in the reaction ${}^{20}\mathrm{Ne}$ + ${}^{12}$C at $E_{\mathrm{lab}}=$ 145, 158, 168, 178, and 200 MeV (from top to bottom, respectively). The arrow corresponds to the position of the peak of the Gaussian distribution.

Figure 2

The c.m. angular distributions of the B and C fragments obtained at $E_{\mathrm{lab}}=$ 145, 158, 168, 178, and 200 MeV (from (a) to (e), respectively). Solid circles correspond to experimental data and the solid curves are $f({\theta }_{\mathrm{c.m}.}$) ∼ 1/sin${\theta }_{\mathrm{c.m}.}$ fit to the data.

Figure 3

Average $Q$ values of the B and C fragments obtained at $E_{\mathrm{lab}}=$ 145, 158, 168, 178, and 200 MeV (denoted by inverted triangle square, diamond, triangle, and circle, respectively) plotted as a function of c.m. emission angle.

Figure 4

The excitation functions for the angle-integrated yield of the carbon and boron fragments. Triangles are the present data; lower energy data (shown by solid points) have been taken from [8]. In the left side of the figure, solid, dashed and dash-dot-dotted curves are the predictions of the statistical model with $l=l_{\mathrm{cr}},l=l_{\mathrm{gr}},$ and the equilibrium orbiting model, respectively. Solid curves in the right side of the figure are EHFM predictions.

Figure 5

Bombarding energy dependence of the average $Q$ values. The solid line shows the linear dependence of $\langle Q\rangle$ with bombarding energy. The $\langle Q\rangle$ values at lower energies are taken from [9].