Resonance strength measurements and thermonuclear reaction rates for 25Mg(p, γ) 26Al

Abstract

The strengths of resonances in 25Mg(p, γ) 26Al in the energy range E p = 317–591 keV have been obtained. Resonance strengths at E p = 317, 387, 433 and 591 keV have been measured absolutely. The strengths of resonances at E p = 591 and 433 keV were also deduced by comparison with the strength of the resonance at E p = 620 keV in 30Si(p, γ) 31P. Relative measurements of 10 resonances in the range E p = 317–591 keV were made. A search for (p, γ) strengths below E p = 300 keV was undertaken and an upper limit for the sum of all possible strengths is given. Thermonuclear reaction rates are calculated for the reaction 25Mg(p, γ) 26Al leading to both the ground state and isomeric first excited state of 26Al in the temperature range T = 5 × 10 7−5 × 10 8 K and are compared with rates determined from cross sections obtained from statistical-model calculations. The superelastic and inelastic scattering of protons is investigated as a mechanism by which the 26Al nucleus may attain a thermal distribution of excited states and is shown to be ineffective.