Orbital electron capture decay of hydrogen- and helium-like ions

The orbital electron capture decay of hydrogen- and helium-like ions is analyzed theoretically. For the general case of allowed nuclear transitions, we calculate the ratio of the decay rate for a helium-like ion to the decay rate for a hydrogen-like ion. We demonstrate that in some cases the decay probability for a nucleus with a single bound electron can be larger than that for the same nucleus with two bound electrons. The possibilities of experimental verification of our predictions are briefly discussed.