Some nuclei undergo radioactive decay by capturing an electron from the К or L shell of the atomic electron orbits. This results in the transformation of a proton to a neutron, the ejection of an unobservable neutrino of definite energy, and the emission of an x-ray where the electron vacancy of the К or L shell is filled by an atomic electron from an outer orbit. Because the net change in the radionuclide species is from atomic number Z to Z— 1, similar to the nuclide change from positron emission, electron capture generally competes with all cases of positron beta decay.