Double electron capture

Double electron capture is a type of double beta decay, a permissible decay mode of an atomic nucleus. For a nuclide (A, Z) with a number of nucleons A and atomic number Z, double electron capture is only possible if the mass of the nuclide (A, Z−2) is lower.

In the ordinary mode, two of the orbital electrons are captured via the weak interaction by two protons in the nucleus, forming two neutrons and two neutrinos. Since the protons are changed to neutrons, the number of neutrons increases by two, while the number of protons Z decreases by two, and the atomic mass number A remains unchanged - the same as two successive electron captures. As a result, by reducing the atomic number by two, double electron capture transforms the nuclide into a different element.

Example:

130 56Ba

+

2 e−

→

130 54Xe

+

2 ν e