Recent studies of the astrophysical site of the s-process suggest a double-pulse s-process in the He-burning shell of low-mass asymptotic giant branch stars, where the C-13(alpha, n) and the Ne-22(alpha, n) neutron sources are active as well. Previous analyses have been performed in terms of a pulsed neutron s-process from intermediate-mass stars. The periodic neutron bursts were ascribed to the Ne-22(alpha, n) reaction only. The current effort is to reformulate the mathematics of the s-process to study the combined effect of repeated double pulses with different properties. Similar to the model of a single-pulse s-process, the effect of the pulses for the double-pulse model shows up at the branchings but, in contrast to the single-pulse model, also at the unbranched s-process path and at isomeric states populated by neutron capture. The new model contains the simpler models as special cases, and it is able to overcome difficulties associated with the single-pulse model.
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H. Beer (1991) studied this question.