Electron capture

Electron capture is a rare type of nuclear decay in which the nucleus captures an electron from the innermost energy level. This electron combines with a proton to form a neutron. The atomic number decreases by one, but the mass number stays the same. The following equation shows the electron capture of polonium-204 (Po-204):

The electron combines with a proton in the polonium nucleus,

creating an isotope of bismuth (Bi-204). The capture of the 1s electron leaves a vacancy in the 1s orbitals. Electrons drop down to fill the vacancy, releasing energy not in the visible part of the electromagnetic spectrum but in the X-ray portion.