(α,Li) Reactions onB11,N15, andF19

Differential cross sections for ($\alpha ,{\mathrm{Li}}^7$) and ($\alpha ,{\mathrm{Li}}^{7*} 0.478$) reactions have been measured on ${\mathrm{B}}^{11}$ to the ground state of ${\mathrm{Be}}^8$, on ${\mathrm{N}}^{15}$ to the ground and first excited states of ${\mathrm{C}}^{12}$, and on ${\mathrm{F}}^{19}$ to the ground state of ${\mathrm{O}}^{16}$, using 42-MeV $\alpha$ particles. In addition, the ($\alpha ,{\mathrm{Li}}^6$) reaction was studied on ${\mathrm{N}}^{15}$, leading to the ground state of ${\mathrm{C}}^{13}$ and on ${\mathrm{F}}^{19}$, leading to the ground and first excited states of ${\mathrm{O}}^{17}$. A zero-range distorted-wave Born-approximation (DWBA) code was used to fit the ($\alpha ,{\mathrm{Li}}^7$) angular distributions assuming a one-step pickup mechanism. Triton reduced widths are extracted from the DWBA calculations normalized to the experimental differential cross sections, and then compared with approximate shell-model calculations. The comparison between the extracted and calculated reduced widths shows that ${\mathrm{B}}^{11}$, ${\mathrm{N}}^{15}$, and ${\mathrm{F}}^{19}$ are probably consistent with a single-particle interpretation, although a small enhancement for triton clustering is observed for the ground state of ${\mathrm{F}}^{19}$.