Strong transfer channels in the ${}^6\mathrm{Li}+{}^{28}\mathrm{Si}$ system at near-barrier energies

Exclusive α-particle and proton production measurements of the system ${}^6\mathrm{Li}+{}^{28}\mathrm{Si}$ are performed at near-barrier energies. Each reaction channel is tagged via a particle-γ coincidence requirement. Ratios of direct to compound contributions are estimated via particle angular distribution measurements. Strong reaction channels for $n$ and $p$ transfer are identified and quantified and found to be described well on a qualitative basis with distorted-wave Born approximation calculations.

Figure 1

γ-ray spectra gated with time to amplitude converter (TAC) and (a) α particles and (b) protons, produced in the ${}^6\mathrm{Li}+{}^{28}\mathrm{Si}$ reaction at $E_{\mathrm{lab}}=13$ MeV.

Figure 2

α-particle spectra observed at ${\theta }_{\mathrm{lab}}={30}^{°}$, gated with TAC and (a) the 1273 keV γ ray of ${}^{29}\mathrm{Si}$, (b) the 2028 keV γ ray of ${}^{29}\mathrm{Si}$, and (c) the 2426 keV γ ray of ${}^{29}\mathrm{Si}$.

Figure 3

Experimental angular distribution (stars) compared with evaporation calculations (solid line) for the ${}^6\mathrm{Li}+{}^{28}\mathrm{Si}$ → ${}^{28}\mathrm{Si}$ + $\alpha +p+n$ reaction at $E_{\mathrm{beam}}=13$ MeV ($\alpha \text{−}\gamma$ coincidences).

Figure 4

Experimental angular distributions ($\alpha \text{−}\gamma$ coincidence measurements) with compound and transfer calculations (see text) for the ${}^6\mathrm{Li}+{}^{28}\mathrm{Si}$ reaction and exit channels (a) and (b) ${}^{29}\mathrm{Si}$+$\alpha +p$ at $E_{\mathrm{beam}}=13$ and 9 MeV, respectively, and (c) and (d) ${}^{29}\mathrm{P}$+$\alpha +n$ at $E_{\mathrm{beam}}=13$ and 9 MeV, respectively. Stars represent the original data, while squares are the so-called new data (original data minus the compound cross sections). Solid lines represent our evaporation calculation; dotted-dashed lines, our DWBA calculation for $n$ and $p$ transfer. The transfer calculations had to be multiplied by factors of 3.5, 4.5, 2.2, and 4.5 for (a), (b), (c), and (d), respectively (see text), in order to best fit the data.

Figure 5

Experimental angular distributions (proton-γ coincidence measurements) with compound and transfer calculations (see text) for the ${}^6\mathrm{Li}+{}^{28}\mathrm{Si}$ → ${}^{32}\mathrm{S}$+$p+n$ reaction at (a) $E_{\mathrm{beam}}=13$ and (b) $E_{\mathrm{beam}}=9$ MeV. Stars represent the original data; squares, the new data (original data minus the compound cross sections). Solid lines represent our evaporation calculation; dotted-dashed lines, our DWBA calculation for α transfer. The transfer calculations had to be multiplied by a factor of 8.5 to best fit the data at 13 MeV. At 9 MeV the evaporation cross sections seem to reproduce well the data.