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Suppose we have a macroscopic solid object. Now we have a beam of Positrons that is injected into this solid Body at vacuum. What can happen?

There will take place a pair Annihilation of electrons and Positrons, causing that energy $E=2m_0c^2$ will be released per annihilated pair. For only a few electron-positron annihilations the solid Body might heat up on the Annihilation Region. But can there occur some interesting phenomena?

I have heard that Positron-emmision tomography is used in medicine. Is there something Special if a few Positrons hit our Body? What would happen if a few (i.e. not that much that death is caused) Positrons would hit the human Body?

kryomaxim
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  • When positrons and electrons annihilate, they produce two gammas that are moving in opposite direction (because of momentum conservation). By correlating the directions and arrival times one can reconstruct a complete 3d scan from the signals of the gamma detectors. The positrons in medical use are not from a beam but they come from injecting a PET radiotracer isotope: https://en.wikipedia.org/wiki/List_of_PET_radiotracers/. – CuriousOne Mar 05 '16 at 20:44
  • @CuriousOne: there are two primary decay modes, one with two gammas, the other with three; it depends upon the orientation of the electron-positron spins, though it is possible in both cases to annihilate and produce additional photons beyond the usual 2 or 3. – Peter Diehr Mar 05 '16 at 20:53
  • @PeterDiehr: True, I just didn't want to confuse the OP about the para- and ortho-positronium bound states. In practice the triplet decay seems to be happening only in a small fraction (<1%?) of all cases and I would suspect that the medical imagers are throwing it into the "background" bin when they detect one. We have an article about that: http://physics.stackexchange.com/questions/71856/why-does-positronium-decay-into-2-photons-more-often-than-into-3-photons. I think you could write a complete answer about that. – CuriousOne Mar 05 '16 at 21:05

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