The differential cross sections of the ${\mathrm{Be}}^9({\mathrm{Li}}^6, \alpha ){\mathrm{B}}^{11}$ reaction have been measured as a function of energy and angle. The $\alpha$ particles leaving the ${\mathrm{B}}^{11}$ in the ground state, ${\alpha }_0$, in the first excited state, ${\alpha }_1$, and in the second and third excited states, ${\alpha }_2+{\alpha }_3$, were observed at 10° intervals from 10° to 160° (lab system) at ${\mathrm{Li}}^6$ energies of 3.00, 3.25, and 3.50 Mev, and at 20°, 60°, 90°, 120°, and 160° (c.m. system) at ${\mathrm{Li}}^6$ energies of 2.00, 2.50, 3.75, and 4.00 Mev. The angular distributions of the ${\alpha }_0$ and ${\alpha }_1$ groups are asymmetric about 90° c.m. Relative maxima occur at both large and small angles for each of the $\alpha$-particle groups, with the yields at large angles being comparable to those at small angles. In all cases the angular distribution varies slowly with bombarding energy and the yields at each angle increase monotonically with increasing energy. At 3.50 Mev the total cross sections are 0.97±0.38 mb for ${\alpha }_0$ and 0.65±0.26 mb for ${\alpha }_1$. The experimental results suggest that the reactions proceed mainly by direct-interaction mechanisms. The similarity of the angular distributions of the ${\mathrm{Be}}^9({\mathrm{Li}}^6, \alpha ){\mathrm{B}}^{11}$ and the ${\mathrm{Be}}^9({\mathrm{He}}^3, p){\mathrm{B}}^{11}$ reactions is pointed out.

• Received 24 August 1960

DOI:https://doi.org/10.1103/PhysRev.121.246