An expansion cloud chamber containing oxygen gas at $\frac{1}{3}$ atmosphere pressure was used to study the reaction ${\mathrm{O}}^{16}+p\to p+4\mathrm{}\alpha$ at a bombarding energy of 28.9 Mev. Two hundred and twelve events were obtained that satisfied the criteria of energy and momentum balance. Ninety-one of these had all five outgoing prongs visible, while the remaining 121 had but four prongs visible, the fifth being obscured by the beam. Slightly more than half of all the events showed the presence of the ground state of ${\mathrm{Be}}^8$. Of these, five events showed the presence of two ${\mathrm{Be}}^8$ nuclei in the ground state. The events exhibiting the presence of a single ground-state ${\mathrm{Be}}^8$ were interpreted according to the mechanism ${\mathrm{O}}^{16}+p\to p+2\mathrm{}\alpha +{\mathrm{Be}}^8$; ${\mathrm{Be}}^8\to 2\alpha$. The possibility of a compound state was considered. If such an intermediate state did occur, it was such that it did not obey strictly the predictions of the compound-nucleus theory. The remaining half of the events did not show evidence for any intermediate nuclei (with the possible exception of the appearance of the 1.4-Mev state of ${\mathrm{B}}^9$ in 5%, or fewer, of the cases) and could be interpreted only on the basis of the direct quadripartition of the oxygen nucleus.

• Received 26 October 1960

DOI:https://doi.org/10.1103/PhysRev.122.139