The angular correlation of the first-emitted $\alpha$ and an $\alpha$ from the sequential decay of the ${}_{}{}^8{}_{}{}^{}\mathrm{Be}_{2.9}^{}{}_{}{}^{}$ state in the reaction ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}(d,\alpha ){}_{}{}^8{}_{}{}^{}\mathrm{Be}_{2.9}^{}{}_{}{}^{}\left(\alpha \right){}_{}{}^4{}_{}{}^{}\mathrm{He}$ strongly suggests that this reaction proceeds by compound-nucleus formation at $E_d=0.4\mathrm{}$ MeV and by a deuteron-pickup direct interaction at $E_d=1.0\mathrm{} \mathrm{and} 1.5$ MeV. The observed symmetry axis for the ${}_{}{}^8{}_{}{}^{}\mathrm{Be}_{2.9}^{}{}_{}{}^{}$ breakup distribution in its own center of mass is compared to the momentum-transfer and recoil directions associated with various possible mechanisms and appears to provide the necessary information to select the mechanism.

• Received 28 July 1971

DOI:https://doi.org/10.1103/PhysRevLett.27.820