Internal conversion occurs when an excited nucleus ejects a low level electron from the first 2 low energy shells such as a $k$-shell electron instead of emitting gamma when returning to ground state. Normally this is associated with heavy elements as the low level electron wave function is more likely to come under the influence of the nucleus.

Can this also occur for light elements such as Lithium, Beryllium, Boron etc? Particularly if they are in a suitably excited state.

If so, can a valence electron from the 2nd shell be emitted directly by internal conversion?

If so what would happen if that valence electron is being used in a molecular or crystal bond?

A) would the internal conversion be inhibited?

B) would the valence electron be emitted?

C) would the kinetic energy instead be distributed between the different atoms in the bond and cause the bond to vibrate or break?

Note that for heavier elements where the electron affected by internal conversion is not directly the valence electron, I suppose the valence electron would be ejected normally. There would then be different indirect effects as the electrons rearrange themselves to the lower energy level possibly with auger photon emission. This would also then affect the valence electron indirectly. I'm also curious on what would happen with heavy atoms due to the loss of valence electron this way but mainly interested in what happens with light atoms with valence electrons directly affected by internal conversion.

  • $\begingroup$ Note that light nuclei have many fewer bound excitations than heavy nuclei, and are therefore more likely to decay by nucleon or cluster emission. Perhaps related. $\endgroup$
    – rob
    Jan 26, 2023 at 4:35

1 Answer 1


Well your reasoning is completely justified and valid. I am going to provide you with some elements to answer more what you want to know, but the exact response would depend on the case under study, and you will see why.

Internal conversion happens mainly in heavy nuclei because they have electrons deeply bound, and their ionization energies are higher, which is important because normally nuclear gamma is more energetic than atomic spectrum. It also happens that heavier nuclei also have a more complex energy spectrum, where vibrational and rotational levels are wider and therefore their spectrum is more dense or "continuous-like". They also have low-lying energy level, so this allows that the spectrum of emission of the nucleus can actually overlap with the absorption spectrum of the electronic cloud.

The opposite happens for lighter nuclei, where the low-lying energy levels are scarce, and normally not present, meaning their lowest level emission is already too energetic to be captured by their own electrons. Also because their lowest electrons (the strongest bound) are not that low-lying as in the heavier nuclei and would need smaller energies of photons to get out. So these two effects influence in reducing the possibilities for light nuclei to undergo internal conversion.

So you see, the guideline is to check the lowest part of the nuclear spectrum and the highest part of the atomic spectrum and see if they overlap, which will say much of the possibilities for internal conversion to occur. Even further, with this information, it would be needed to account for angular momentum dependence of the interaction of photons with the electrons, which is not simple.

Finally, the knowledge of the spectrum is tabulated, but no general rule that is sufficiently reliable will reproduce the tabulated data. So you would have to match them for any specific case and check their overlapping.

As for molecular levels, you would need to do the same, but electrons in a molecular cloud should be weakly bound, specially those involved in the molecular bounds. So in the end it all comes to the low-lying electrons, which are pretty much unchanged when nuclei in molecules.


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