Described in this thesis are measurements made of the thick-target neutron yield from the reaction 13C(α, n)16O.The yield was determined for laboratory bombarding energies between 0.475 and 0.700 MeV, using a stilbene crystal neutron detector and pulse-shape discrimination to eliminate gamma rays.Stellar temperatures between 2.5 and 4.5 x 108 oK are involved in this energy region.From the neutron yield was extracted the astrophysical cross-section factor S(E), which was found to fit a linear function: S(E) = [(5.48 ± 1.77) + (12.05 ± 3.91)E] x 105 MeV-barns, center-of-mass system.The stellar rate of the 13C(α, n)16O reaction if calculated, and discussed with reference to helium burning and neutron production in the core of a giant star.
Results are also presented of measurements carried out on the reaction 9Be(α, n)12C, taken with a thin Be target.The bombarding energy-range covered was from 0.340 to 0.680 MeV, with excitation curves for the ground- and first excited-state neutrons being reported.Some angular distributions were also measured.Resonances were found at bombarding energies of ELAB = 0.520 MeV (ECM = 0.360 MeV, Γ ~ 55 keV CM, ωγ = 3.79 eV CM) and ELAB = 0.600 MeV (ECM = 0.415 MeV, Γ ˂ 4 keV CM, ωγ = 0.88 eV CM).The astrophysical rate of the 9Be(α, n)12C reaction due to these resonances is calculated.
