Alpha-particle emission associated with the $\beta$ decay of ${\mathrm{B}}^{12}$ has been detected and the energy spectrum investigated. These studies show that (1.3±0.4)% of all decays of ${\mathrm{B}}^{12}$ lead to the second excited state of ${\mathrm{C}}^{12}$ and that this state breaks up predominantly into three alpha particles with one alpha particle and the ground state of ${\mathrm{Be}}^8$ as an intermediate stage in the process. The most probable spin and parity assignments for the state appear to be $J=0^{+}$, and analysis of the alpha-spectrum yields $Q({\mathrm{C}}^{{12}^{*}}-{\mathrm{Be}}^8-{\mathrm{He}}^4)=278\mathrm{}\pm 4$ kev, corresponding to an excitation energy in ${\mathrm{C}}^{12}$ of 7.653±0.008 Mev. A new determination of the disintegration energy of ${\mathrm{Be}}^8$ yields $Q({\mathrm{Be}}^8-2\mathrm{}{\mathrm{He}}^4)=93.7\mathrm{}\pm 0.9$ kev and hence $Q({\mathrm{C}}^{{12}^{*}}-3\mathrm{}{\mathrm{He}}^4)=372\mathrm{}\pm 4$ kev. It is concluded, from the general principle of reversibility of nuclear reactions, that the second excited state of ${\mathrm{C}}^{12}$ as predicted by Hoyle is of a suitable character to act as a stellar thermal resonance in the Salpeter process, 2${\mathrm{He}}^4$⇌${\mathrm{Be}}^8$; ${\mathrm{Be}}^8(\alpha , \gamma ){\mathrm{C}}^{12}$ under conditions expected in red giant stars.

• Received 25 March 1957

DOI:https://doi.org/10.1103/PhysRev.107.508