2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/181420Neutron stars, with their strong surface gravity, have interestingly short timescales for the sedimentation of heavy elements. Recent observations of unstable thermonuclear burning (observed as X-ray bursts) on the surfaces of slowly accreting neutron stars ($< 0.01$ of the Eddington rate) motivate us to examine how sedimentation of CNO isotopes affects the ignition of these bursts. We further estimate the burst development using a simple one-zone model with a full reaction network. We report a region of mass accretion rates for weak H flashes. Such flashes can lead to a large reservoir of He, the unstable burning of which may explain some observed long bursts (duration $\sim 1000$ s).6 pages, 2 figures, submitted to the proceedings of the conference "The Multicoloured Landscape of Compact Objects and Their Explosive Origins'', 2006 June 11--24, Cefalu, Sicily (Italy), to be published by AIPAstrophysicstext