Beta Decay - Electron Capture (K-capture)

Electron Capture (K-capture)

In all the cases where β+ decay is allowed energetically, the electron capture process, when an atomic electron is captured by a nucleus with the emission of a neutrino, is also allowed:

$^A_ZN + e^- \rightarrow ~ ^{~~~A}_{Z-1}N' + {\nu_e}$

The emitted neutrino is mono-energetic. In proton-rich nuclei where the energy difference between initial and final states is less than 2m_ec2, β+ decay is not energetically possible, and electron capture is the sole decay mode.

This decay is also called K-capture because the innermost electron of an atom belongs to the K-shell of the electronic configuration of the atom, and this has the highest probability to interact with the nucleus.

There is an analogous process possible in theory in antimatter: antiproton-rich antimatter radioisotopes might decay via an analogous process of positron capture, but in practice no such complex antimatter nuclides have either been discovered or artificially constructed.