Stellar evolution calculations confirm that semiconvection will occur below the convective envelope of a low-mass, low-metallicity AGB star, after a thermal pulse. These calculations show how semiconvection leads to the creation of a “13C layer” in the star, which can provide a potent source of neutrons (via the 13C[a, n]160 reaction) in a convective shell during later evolution. The rate at which neutrons are released is largely determined by the rate at which the 13C layer is introduced into the convective shell. The 13C neutron source maintains neutron densities of 109-1010 n/cm3 for ∼ 10 years. This provides a neutron exposure r=0.15 mb“1 during most of the pulses calculated. Because of the strong filtering effect by light elements, only 10—20% of the neutrons produced will be captured by iron-seed nuclei, each such nucleus capturing 4–5 neutrons per pulse.