Electron capture is a type of radioactive decay in which an atomic nucleus absorbs an inner-shell electron. This process typically occurs in unstable isotopes, where the nucleus has too many protons compared to neutrons. When the electron is captured, it combines with a proton to form a neutron, resulting in a decrease in the atomic number and a transformation into a different element. As a result of electron capture, the atom emits a neutrino, which is a nearly massless particle. This decay process can lead to the emission of X-rays when outer-shell electrons fill the vacancy left by the captured electron. Overall, electron capture plays a significant role in the stability of certain isotopes.