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Why only gamma radiation ?

  1. Mar 9, 2012 #1

    PhysicoRaj

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    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?
     
  2. jcsd
  3. Mar 9, 2012 #2
    Re: Why only gamma radiation....?

    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.
     
  4. Mar 9, 2012 #3

    cmb

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    Re: Why only gamma radiation....?

    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.
     
  5. Mar 9, 2012 #4

    Vanadium 50

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    Re: Why only gamma radiation....?

    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.
     
  6. Mar 15, 2012 #5

    PhysicoRaj

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    Re: Why only gamma radiation....?

    Thank you guys.
     
  7. Mar 15, 2012 #6
    Re: Why only gamma radiation....?

    Just for curiosities sake, there are some freaky low energy nuclear transitions like this: http://www.thorium.at/?page_id=4 [Broken]. 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.
     
    Last edited by a moderator: May 5, 2017
  8. Mar 18, 2012 #7
    Re: Why only gamma radiation....?

    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.
     
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