A methane-filled expansion cloud chamber, operated at $\frac{1}{3}$ atmosphere, was used to study the ${\mathrm{C}}^{12}+p\to p+3\mathrm{}\alpha$ reaction. Two hundred events that satisfied momentum and energy conservation were accepted for analysis. One hundred forty-eight of these had all four prongs visible; the remaining fifty-two had only three visible prongs with the fourth prong directed into an invisible region of the chamber. One-quarter of the events proceeded via the ${\mathrm{Be}}^8$ ground state and at least one-half via the 2.9-Mev level in ${\mathrm{Be}}^{8*}$; possibly higher levels in ${\mathrm{Be}}^8$ were also involved. Evidence for the participation of levels in ${\mathrm{C}}^{12}$ at 9.6, 16, 20, and 25 Mev was found. There is evidence that the ${\mathrm{C}}^{12}(p, \alpha ){\mathrm{B}}^9$ reaction also participates, with levels at 0 and 3.2±1.0 Mev. The possibility of the ${\mathrm{C}}^{12}+p\to {\mathrm{Li}}^5+{\mathrm{Be}}^8$ reaction was investigated and it was concluded that it could account for at most five percent of the events. At least one example of the ${\mathrm{C}}^{13}(p, d)3\mathrm{}\alpha$ reaction was seen.

• Received 24 May 1955

DOI:https://doi.org/10.1103/PhysRev.99.1356