difference between electron capture and positron emission

A second reason is that the only detectable particles created in this process are X-rays and Auger electrons that are emitted by the excited atomic shell. One reason is that the probability of double electron capture is stupendously small the half-lives for this mode lie well above 10 20 years. There exist 34 naturally occurring nuclei that are believed to undergo double electron capture, but the process has been confirmed by observation in the decay of only three nuclides: 78 When all other modes are “forbidden” (strongly suppressed) double electron capture becomes the main mode of decay. In most cases this decay mode is masked by other, more probable modes involving fewer particles, such as single electron capture. As a result, by reducing the atomic number by two, double electron capture transforms the nuclide into a different element. 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. In this mode of decay, two of the orbital electrons are captured via the weak interaction by two protons in the nucleus, forming two neutrons (Two neutrinos are emitted in the process). 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.

Double electron capture is a decay mode of an atomic nucleus.

Difference between electron capture and positron emission