2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/168980The purpose of this paper is to calculate the two-photon decay rate corresponding to the two-photon transitions nS->1S and nD->1S in hydrogenlike ions with a low nuclear charge number Z (for principal quantum numbers n = 2,...,8. Numerical results are obtained within a nonrelativistic framework, and the results are found to scale approximately as (Z alpha)^6/n^3, where alpha is the fine-structure constant. We also attempt to clarify a number of subtle issues regarding the treatment of the coherent, quasi-simultaneous emission of the two photons as opposed to one-photon cascades. In particular, the gauge invariance of the decay rate is shown explicitly.10 pages, LaTeXAtomic PhysicsAstrophysicstext