B¹², C¹², and the Red Giants

Alpha-particle emission associated with the β decay of B¹² has been detected and the energy spectrum investigated. These studies show that (1.3±0.4)% of all decays of B¹² lead to the second excited state of C¹² and that this state breaks up predominantly into three alpha particles with one alpha particle and the ground state of Be⁸ 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(C^12*-Be⁸-He⁴)=278±4 kev, corresponding to an excitation energy in C¹² of 7.653±0.008 Mev. A new determination of the disintegration energy of Be⁸ yields Q(Be⁸-2He⁴)=93.7±0.9 kev and hence Q(C^12*-3He⁴)=372±4 kev. It is concluded, from the general principle of reversibility of nuclear reactions, that the second excited state of C¹² as predicted by Hoyle is of a suitable character to act as a stellar thermal resonance in the Salpeter process, 2He⁴⇌Be⁸; Be⁸(α, γ)C¹² under conditions expected in red giant stars.