In a neutron-rich, α-rich environment that could arise during a supernova explosion the reaction chain ${}_{}{}^4{}_{}{}^{}\mathrm{He}$(αn,γ${)}^9$Be(α,n${)}^{12}$C dominates the creation of carbon, which leads to the creation of heavier elements in the subsequent r process [S. E. Woosley and R. D. Hoffman, Astrophys. J. 395, 202 (1992); B. S. Meyer, G. J. Matthews, W. M. Howard, S. G. Woosley, and R. D. Hoffman, ibid. 399, 656 (1992); W. M. Howard, S. Goriely, M. Rayet, and M. Arnould, ibid. 417, 713 (1993)]. For this reason the excitation function of the reaction ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$(α,n${)}^{12}$C has been measured in the energy range from ${\mathit{E}}_{\mathrm{\alpha }}$=366 keV up to 3552 keV (corresponding ${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$=254–2450 keV in the center-of-mass system) to obtain consistent data in the whole range, which were lacking in the literature. The measurements have been performed with a 4π detector and the yield contributions of the ${\mathit{n}}_0$ and ${\mathit{n}}_1$ neutron group could be resolved. Solid metallic targets of thickness 430 Å (7.75 μg/${\mathrm{cm}}^2$) and 650 Å (11.72 μg/${\mathrm{cm}}^2$) were used. Reaction rates and an analytic expression for them have been evaluated for 0.001≤${\mathit{T}}_9$≤10. © 1996 The American Physical Society.

• Received 10 October 1995

DOI:https://doi.org/10.1103/PhysRevC.53.2486