double electron capture

Double electron capture is a decay mode of atomic nucleus.

There exist 35 naturally occurring isotopes that can undergo double electron capture.

It occurs simultaneously with double electron capture, their branching ratio depending on nuclear properties.

By changing the number of protons, double electron capture transforms the nuclide into a new element.

Thus, the experimental detection of double electron capture is more difficult than that for double beta decay.

One reason is that the probability of double electron capture is enormously small (the theoretical predictions of half-lives for this mode lies well above 10 years).

Fe is observationally stable, with a branching theory that it decays to Cr, with a half-life of more than 3.1x10 years via double electron capture (2β).

However, if the lepton number is not conserved, or the neutrino is its own antiparticle, another kind of the process can occur: the so-called neutrinoless double electron capture.

The other three are Cd, Cd (both double electron capture), and Cd (double beta decay); only lower limits on their half-life times have been set.

For some nuclei, the process occurs as conversion of two protons to neutrons, with emission of two electron neutrinos and absorption of two orbital electrons (double electron capture).

In most cases this decay mode is masked by more probable modes (single electron capture etc.), but when all these modes are forbidden or strongly suppressed, double electron capture becomes the main mode of decay.

A for alpha decay, B for beta decay, BB for double beta decay, E for electron capture, EE for double electron capture, IT for isomeric transition. '

The above described process with capture of two electrons and emission of two neutrinos (two-neutrino double electron capture) is allowed by the Standard Model of particle physics: no conservation laws (including lepton number conservation) are violated.