Study of the ${\mathrm{C}}^{12}(p,p\alpha ){\mathrm{Be}}^8$ Reaction and Excited States of ${\mathrm{C}}^{12}$

The ${\mathrm{C}}^{12}(p,p\alpha ){\mathrm{Be}}^8$ reaction has been studied for several proton and $\alpha$-particle angles using a bombarding energy of 57 MeV. It is found that the reaction proceeds primarily by sequential $\alpha$ decay, i.e., the proton inelastically scatters, leaving ${\mathrm{C}}^{12}$ in an excited state which then decays by emitting an $\alpha$ particle. The properties of several of the excited states of ${\mathrm{C}}^{12}$ in the giant dipole region were investigated. States at 19.7, 21.1, 22.2, and 26 MeV were found which have a significant $T=0\mathrm{}$ component. In addition, the ${\mathrm{C}}^{12}(p,2p\alpha ){\mathrm{B}}^{11}$ reaction was measured simultaneously. These data indicate that a ${\mathrm{C}}^{12}$ state at 20.3 MeV decays to the ground state of ${\mathrm{B}}^{11}$ by proton emission.