Determination of the 9Be(α,n)12C reaction rate

In a neutron-rich, α-rich environment that could arise during a supernova explosion the reaction chain 4He(αn,γ)9Be(α,n)12C 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 9Be(α,n)12C has been measured in the energy range from Eα=366 keV up to 3552 keV (corresponding Ec.m.=254 endash 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 n0 and n1 neutron group could be resolved. Solid metallic targets of thickness 430 A (7.75 μg/cm2) and 650 A (11.72 μg/cm2) were used. Reaction rates and an analytic expression for them have been evaluated for 0.001≤T9≤10. copyright 1996 The American Physical Society