Double electron capture

The double electron capture is a possibility of the radioactive decay of an atomic nucleus. For a nuclide (A, Z) with the number of nucleons A and atomic number Z is a double electron capture is only possible if the mass of the nuclide (A, Z -2) is smaller.

In this decay pathway two orbital electrons are captured by two protons of the nucleus and there are two neutrons. Two neutrinos are released. Since the protons are converted into neutrons, the number of neutrons increases by 2, the number of protons Z decreases by 2 and the atomic mass A remains unchanged. By changing the number of protons produced during double electron capture nuclide of another element.

Example:

Usually this decay pathway is covered by probable paths ( for example, single electron ). But if these decay pathways are forbidden or strongly suppressed, then the double electron capture of Hauptzerfallsweg. There are 35 naturally occurring isotopes in which the double electron capture can occur. Nevertheless, the process has been experimentally demonstrated only recently. One reason for this is that the probability of double electron decay is extremely small. The theory predicts a half-life for this decay pathway of over 1020 years. The second reason is that the only detectable particles in this case - quanta and Auger electrons are emitted from the atomic shell are. In the energy range (~ 1-10 keV), the background noise is unusually high. Therefore, the experimental evidence is more difficult than that of the double beta decay

If the mass difference between parent and daughter atom more than two electron masses is ( 1.022 MeV ), the resulting energy is large enough to allow an electron capture with positron emission. It passes the same to twice the electron. The ratio of the frequencies of the two paths depends on the disintegration properties of the nucleus. If the mass difference is more than 4 electron mass is ( 2.044 MeV), a third decay pathway is - the double positron decay possible. Only six naturally occurring nuclides can decay via all three ways.

Neutrino double electron capture Loser

The process described above with the capture of two electrons and the emission of two neutrinos is allowed by the standard model of elementary particle physics, because there are no conservation laws ( the conservation of lepton number included) injured.

However, could, if the lepton number would not get another operation to occur: The resulting energy is released within the core as bremsstrahlung (gamma radiation) and it will be sent no neutrinos. This decay pathway could not be demonstrated experimentally so far. He would contradict the standard model.

• Radioactivity