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Natural Science Forum / Physics / Particle Physics / August 2004511 kev line - why not 1022 kev?
When an electron and a positron annihilate, one speaks of the 511 kev peak. But a mass equal to 1022 kev gets destroyed, so i am wondering why we see a peak at 511 kev? to conserve stuff they create two photons. > When an electron and a positron annihilate, one speaks of the 511 kev peak. > But a mass equal to 1022 kev gets destroyed, so i am wondering why we see a > peak at 511 kev? Dear Christian, >When an electron and a positron annihilate, one speaks of the 511 kev peak. >But a mass equal to 1022 kev gets destroyed, so i am wondering why we see a >peak at 511 kev? This is because electron-positron annihilation should yield at least two photons. (As a side-note: more than two photons should be possible but should only happen in a tiny minority of annihilation events.) So, each photon gets half the energy. That it is impossible to produce just one photon is because one can always get to the rest frame of the electron-positron system. In that frame the center of mass is at rest. The resulting single photon, should therefore also be at rest. However, photons move with the speed of light. Hence, it is not possible to produce a single photon. Best, Chris But one photon can gives the electron-positron pair. Does it reveal something special here? What this reversal reveals? Would it be possible that this is the internal structure of light? > Dear Christian, > [quoted text clipped - 14 lines] > Best, > Chris Dear Funland, >But one photon can gives the electron-positron pair. >Does it reveal something special here? >What this reversal reveals? >Would it be possible that this is the internal structure of light? In vaccuum one photon cannot give an electron-positron pair, by exactly the same argument as I gave below. It is, however, possible in de neighbourhood of a nucleus. This is all just QED, so is not related to to structure of the photon. Best, Chris >"Chris Dams" <chrisd@gamow.sci.kun.nl> ??? > [quoted text clipped - 13 lines] >> photons move with the speed of light. Hence, it is not possible to >> produce a single photon. > But one photon can gives the electron-positron pair. > Does it reveal something special here? > What this reversal reveals? > Would it be possible that this is the internal structure of light? It certainly does hint to as much, and the idea was definitely discussed in the 1930's, when positrons were conclusively identified. De Broglie proposed a very coherent theory on this subject in the 1930's, but his ideas went against the main current of ideas at the time, so his theory was simply ignored. If you are interested in his ideas on this subject, I discussed the structure proposed by de Broglie with FrediFizzx in another thread in this newsgroup a while back. The thread name was "Photon Zero Mass & E=MC**2 ?" http://groups.google.com/groups?hl=fr&lr=&ie=UTF-8&threadm=562f286c.0401260949.6 51688e4%40posting.google.com&rnum=1&prev=/groups%3Fq%3Dmichaud%2Bfredifizzx%2Bbr oglie%2Bgroup:sci.physics.particle%26hl%3Dfr%26lr%3D%26ie%3DUTF-8%26group%3Dsci. physics.particle%26selm%3D562f286c.0401260949.651688e4%2540posting.google.com%26 rnum%3D1 André Michaud >When an electron and a positron annihilate, one speaks of the 511 kev peak. >But a mass equal to 1022 kev gets destroyed, so i am wondering why we see a >peak at 511 kev? The 1022 keV comes out as two 511-keV photons, moving in opposite directions in the center-of-momentum frame. Switching to the lab frame, the photons usually still come out in very different directions. If you stick a scintillation counter or whatever near the source, it's unlikely that both photons will enter the detector. So we "see" only 511 keV.  SignatureJon Bell <jtbellm4h@presby.edu> Presbyterian College Dept. of Physics and Computer Science Clinton, South Carolina USA > When an electron and a positron annihilate, one speaks of the 511 kev peak. > But a mass equal to 1022 kev gets destroyed, so i am wondering why we see a > peak at 511 kev? "annihilate" and "destroyed" must be put in perspective. The energy making up the mass of both particles presently "converts" to pure energy state. The reason why the peaks are at .511 MeV relates to the manner in which positronium decays. When the spin of both particles is aligned parallel, the system is named ortho-positronium and always decays into 3 .34 MeV photons, with decay time of 1.5E-7 second. When the spin of both particles is aligned antiparallel, the system is called para-positronium and always decays into .511 MeV 2 photons with approximate decay time of 3E-10 sec. It was also theorized in the 1930's that if a pair combined close to a heavy nucleus, then one 1.022 MeV photon could result, but experimental possibilities at the time did not allow conclusive confirmation. Such verification would be quite easy now since close to molecular thin target material can now easily be produced, but since it is against current orthodox philosophy in physics to do such verification, we unfortunately will not have confirmation for a while yet. André Michaud. |
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