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Despite the positive applications of positrons in nuclear medicine and astronomy, the existence of antimatter seems to raise more questions than it answers. Most recently, a cloud of positrons was discovered in an area of the galaxy in which it should not have been found, and has given particle physicists a new problem to tackle. Positrons are usually created in the presence of large, observable entities: as discussed in the previous page, they can be produced in the high gravitational field of a black hole; and they can be produced during beta (+)-decay in the nucleosynthesis processes in novae and supernovae. The cloud was discovered in an area that lacks any of the objects that could have created the antiparticles. Positrons and electrons can annihilate in two ways: if they annihilate directly they produce two photons (each of which has an energy of 0.511 MeV); if they form positronium- a helium-like atom composed of a positron and an electron in which the positron acts the part of the proton- three photons are produced (each of which has an energy of less than 0.511 MeV). The cloud was observed by NASA's Compton Gamma Ray Observatory, an orbiting telescope equipped with four separate gamma ray instruments designed to observe a large range of gamma-ray energies. One of the instruments is primarily sensitive to gamma rays over the energy range of 0.05-10MeV, and observed the cloud of positrons. Because the positron cloud was discovered in such an unusual location, it is likely that we may discover yet another means by which antiparticles come into existence. |
