We know that when an electron is knocked from the innermost shell of an atom (K - shell), a vacancy is created in the K - Shell. This vacancy in the K - Shell is by an electron falling from an upper shell (usually L-Shell or M-Shell) producing photons due to falling of electron from an upper to a lower orbit. These are called Characteristic X-Rays.


During Electron Capture (or K - Capture) type of β-decay, the nucleus absorbs an inner atomic electron hence converting the nuclear proton to a neutron and emitting an electron neutrino according to the following equation:

$\hspace{6cm}$reaction equation

My question is that when an electron is absorbed by the nucleus it automatically creates a vacancy in its shell, which needs to be filled. Hence does an electron from an upper shell fill the vacancy and emit characteristic X-Rays (and hence energy in addition to decay energy) or is the complete energy released only in the form of energy of the neutrino ?

  • $\begingroup$ Characteristic X-rays are emitted when the electron from the upper shell makes a transition to the inner shell and fills the hole. The neutrino is emitted in the process of proton conversion. $\endgroup$ Oct 19, 2017 at 14:06
  • $\begingroup$ it is a bit tricky question because the nucleus therefore the atom itself changes in such a process, say N turns to C. So in principle all energy levels should change after such a process. I hope someone can answer this question. $\endgroup$ Oct 19, 2017 at 14:11
  • $\begingroup$ X-rays are common efter a change of Z-number of the nucleus, but especially so for electron capture. For example Fe-55, where EC is followed in 25 % of cases by manganese K$\alpha$ emission. nucleardata.nuclear.lu.se/toi/nuclide.asp?iZA=260055 $\endgroup$
    – user137289
    Oct 20, 2017 at 12:53

1 Answer 1


Yes, electron capture can be followed by the emission of a characteristic X-ray. This was first observed by Alvarez [1] (not using the famous bubble chamber he got the Nobel prize for!). Alternatively, an outer electron can be ejected (Auger effect). A thorough review of all theoretical and experimental aspects can be found in [2].

[1] Luis W. Alvarez. Nuclear K electron capture. Phys. Rev., 52:134–135, Jul 1937

[2] W. Bambynek, H. Behrens, M. H. Chen, B. Crasemann, M. L. Fitzpatrick, K. W. D. Ledingham, H. Genz, M. Mutterer, and R. L. Intemann. Orbital electron capture by the nucleus. Rev. Mod. Phys., 49:77–221, Jan 1977.


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