A New Evaluation of the ¹¹ 11 B(p, α )α α α ) α α Reaction Rates

Reaction rates of the ¹¹ B(p, α ) α α process have been evaluated on the basis of a data set spanning incident proton energies Eₚ from 0.15 to 3.8 MeV. A previously published analysis (Spraker et al. in J Fusion Energy 31(4):357, 2012) of these data provided the number of outgoing α -particles in a restricted range of the detected α -energy spectrum, making it unsuitable for the evaluation of the reaction rates. The present work takes advantage of a calculation of the α -energy spectrum based on a sequential model of the reaction and the assumption that the primary α -particles are emitted with =3 . A full description of this ansatz, which has been shown to reproduce the essential features of the observed α -energy spectra, can be found in Stave et al. (Phys Lett B 696:26, 2011). The accuracy of these calculated spectra has made it possible to reliably extrapolate the new data to zero-energy α -particles. In the ensuing calculation of the cross section, the total measured α -yield is then divided by a fixed factor of three at all incident proton energies. In addition, this technique has enabled a treatment of the α ₀ channel where the 12C nuclei decay to the ground state of 8Be via emission of an α -particle. This channel contributes at incident proton energies above 2 MeV. The new cross section data have then been used to evaluate the ¹¹ B(p, α ) α α reaction rates. The new evaluation is ~ 10–15 % higher than the currently accepted result (Angulo et al. in Nucl Phys A 656(1):3, 1999) at temperatures between 200 and 600 keV (2–7 × 10 ⁹ K). The inclusion of a narrow, low-lying resonance at Eₚ=0.162 MeV in the evaluation is found to have a minimal effect on the reaction rate above 100 keV (1.2 × 10 ⁹ K), and a higher-lying state at Eₚ=3.75 MeV is shown to enhance the reaction rates by only ~ 15 % above 400 keV (4.6 × 10 ⁹ K).