Unraveling the Reaction Mechanisms Leading to Partial Fusion of Weakly Bound Nuclei

Collisions between complex nuclei may give rise to their total or partial fusion. The latter case is found experimentally to gain importance when one of the colliding nuclei is weakly bound. It has been commonly assumed that the partial fusion mechanism is a two-step process, whose first step is the dissociation of the weakly bound nucleus, followed by the capture of one of the fragments. To assess this interpretation, we present the first implementation of the three-body model of inclusive breakup proposed in the 1980s by Austern et al. [Phys. Rep. 154, 125 (1987)] that accounts for both the direct, one-step, partial fusion and the two-step mechanism proceeding via the projectile continuum states. Contrary to the widely assumed picture, we find that, at least for the investigated cases, the partial fusion is largely dominated by the direct capture from the projectile ground state.

Figure 1

Illustration of the direct (left) and two-step (right) paths leading to partial capture of the projectile. See text for details.

Figure 2

Nonelastic breakup contribution for the reaction for ${}^{93}\mathrm{Nb}(d,pX)$ at $E_{\mathrm{lab}}=25.5\mathrm{MeV}$ for an outgoing proton c.m. energy of 14 MeV. (a) Energy differential cross section as a function of the neutron-target orbital angular. (b) Double differential cross section angular distribution.

Figure 3

(a) NEB differential cross sections as a function of the $d\text{−}{}^{209}\mathrm{Bi}$ relative energy. (b) Ratio of NEB cross section computed by different methods as a function of the ${}^6\mathrm{Li}$ incident energy. The ellipse highlights the energy corresponding to panel (a). See text for more details.

Figure 4

Ratios of NEB cross section for the $\alpha$-production channel in the ${}^6\mathrm{Li}+{}^{209}\mathrm{Bi}$ reaction as a function of the ${}^6\mathrm{Li}\to \alpha +d$ separation energy.