Why only gamma radiation from nuclear transitions?

[PhysicoRaj]

Why only gamma radiation...?

All the radioactive elements emit either alpha, beta, never both and maybe sometimes gamma with these. But why do they emit gamma rays only? Why not X-Rays?

 

[M Quack]

In principle there is no difference between gamma- and X-rays. Both are "just" electromagnetic radiation. The convention is to call them gamma when they come from the nucleus, and x-rays when they come from electronic transitions.

 

[cmb]

All the radioactive elements emit either alpha, beta, never both

I'd not be surprised if that is generally the case because a nucleus is unstable either beause it is 'neutron heavy' and is prone to emit a beta (a beta is usually from a proton decaying, mediated by the weak force), or 'proton heavy' in which case it will emit a positron or 'it could reduce' the relative p:n ratio by lumping out an alpha.

But I'm pretty sure there are isotopes that emit all types. U238 I seem to recall decays by alpha, double beta and fission.

 

[Vanadium 50]

Ta-180 is predicted to decay via gamma emission. However, the half life is about 10¹⁵ years, and it has not been observed. There are other gamma-only states, but they typically have half-lives that are milliseconds or smaller. Since there is a huge gap, there aren't many isotopes one is likely to be familiar with.

 

[PhysicoRaj]

Thank you guys.

 

[kurros]

Just for curiosities sake, there are some freaky low energy nuclear transitions like this: http://www.thorium.at/?page_id=4 . There is an isomer of Th-229 with an energy only 7.6 eV above the ground state, so when this state relaxes it emits a "gamma ray" of only UV wavelength.

 

[Bob S]

Historically, the term x-ray sometimes applied only to photons from atomic level transitions (up to about 120 keV), and gammas only from nuclear transitions. Now, the term x rays seems to apply to both atomic and nuclear photons.

The decay of beryllium-7 to lithium-7 is a very interesting nuclear decay, in that it emits only an atomic x-ray and a neutrino. Be-7 decays by capturing an electron from the atomic k-shell, and emitting a neutrino. It emits no nuclear gammas and no charged particles (alpha or beta). The x-rays come from outer atomic electons cascading down to fill the k-shell vacancy.