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Is it possible that sometimes all the energy goes to the alpha (or beta) particle so that no gamma rays are emitted and other times part of the energy is emitted as a gamma quant?

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  • $\begingroup$ Absolutely. There are also alternatives to alpha beta gamma, of course. $\endgroup$
    – Matt
    Oct 21, 2015 at 11:58
  • $\begingroup$ The only thing that is unusual about the isotopes that do this is the presence of the "pure" line (the one with no photon at all). Most $\alpha$ and $\beta$ decay channels of heavy isotopes have several different paths each accompanied by a different collection of gammas. Only some include a path with no gamma. $\endgroup$ Oct 21, 2015 at 16:03

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Your answer is, yes ! Alpha or beta decay can happen from parent nucleus directly to the ground state of daughter nucleus.

As very few examples :

  • for alpha decay : 210Po can decay to the ground state of 206Pb emitting an alpha particle of 5.305 MeV (branching ratio of 99.999% that is to say preferd decay mode). It can also decay to an excited level of 206Pb emitting both an alpha (4.502 MeV) and a gamma particle (0.803 MeV) with a branching ratio of 0.001%.

  • for the beta decay : 198Au can decay to the ground state of 198Hg emitting a beta particle only of 1.3723 MeV though happening only 0.025% of the time. The major decay mode, with a branching ratio of 98.99% is to the first excited level of 198Hg : 198Au -> 198Hg + e- (960.5 keV) + gamma (411.8 keV). Other possible beta decay is to the second excited level of 198Hg with a branching ratio of 0.985% : 198Au -> 198Hg + e- (284.6 keV) + gamma (1087.7 keV) or 198Au -> 198Hg + e- (284.6 keV) + gamma (675.9 keV) + gamma (411.8 keV)

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  • $\begingroup$ Thank you! That is what I wanted to know. But why is it that we are tought in school that alpha rays can be blocked by a sheet of paper. That might be true, bu do we always have to protect us against the gamma rays as well, because almost all alpha (and beta) emitting isotopes also emit gamma? $\endgroup$
    – Silja
    Oct 22, 2015 at 8:09
  • $\begingroup$ It is really depeding of the isotope you are working with. But again you are right, in terms of radioprotection you always have to take care of associated gamma particles. With the exmaple of 198Au, a block of few mm of plexiglas will protect you from the beta partcile but not from the gamma rays (either 1087.7 keV, 675.9 keV or 411.8 keV) happening in >99.99% of the time. $\endgroup$ Oct 22, 2015 at 8:19

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