Electron-capture decay description

Delayed fission is also an exotic nuclear decay process of heavy nuclei that is observed subsequent to P or EC decay. In the delayed fission process, P decays or electron captures (EC) of the parent nuclide populate excited states of the daughter nucleus, and if these states are of energies comparable to or greater than the fission barrier of the daughter nucleus, then fission may compete with other decay modes of the excited states. The process is schematically shown in O Fig. 18.12. Reviews give a detailed description of delayed fission (Oganessian and Lazarev 1985 Hall and Hoffinan 1992). 

Here is a description of the process as given by Helf when an explosive is irradiated with fast neutrones a nucleus captures the incident fast neutron and ejects two slow neutrons. The resulting nucleus N is radioactive and decays with a 10 min half-life to stable C. In this last transition a positron 0 is emitted. Because of its opposite charge, the 0 is strongly attracted by the nearby electron in the resulting collision, both the positron and electron are annihilated and in that process the masses of colliding particles are converted into two 0.511 MeV quanta of electromagnetic radiation. 

We focus here into the radiative processes that modify the ion charge state, i.e., those that involve the capture of an electron from the target valence band. We do not include radiative relaxation processes in which one electron decays between two bound states of the ion, although they can be of the same importance in the description of a realistic neutralization and relaxation... 

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