Nucleosynthesis in explosive hydrogen burning and its implications in ten-minute interval of x-ray bursts

Nucleosynthesis during combined hydrogen and helium shell flashes on accreting neutron stars is investigated as one of the possible mechanisms of Type I X-ray bursts. During the flash, 64Ge and 68Se are synthesized through rapid proton captures and positron decays. Their half-lives, 64 s and 1.6 min, are long enough as compared with the duration of the flash. The end product of the flash consists mainly of the daughter nuclei of 64Ge and 68Se, i.e., 64Zn and 68Ge, and of either 1H or 4He. Unburnt 1H and 4He can be saved as nuclear fuel which will be used in the succeeding flash. The observed short time interval (- 10 min) in some Type I X-ray bursts may be interpreted by means of such reservoir of the nuclear fuel. (author)