A Beginner's Guide
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        Although still considered somewhat exotic particles, positrons
(the antiparticles of electrons) and positronium (the bound state of an electron
and a positron) are currently employed in the exploration of a variety of physical
phenomena.
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        For instance, positron emission tomography (PET) is a well
established medical technique used to study the human brain and investigate brain
disease.
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        Positrons are also important as non-destructive diagnostic
tools of industrially important materials.
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        In addition, the detection of annihilation lines of positrons
and positronium emanating from the centre of our galaxy renders their interaction
with matter of interest to astrophysicists.
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        Of course, the positron is also an essential ingredient
for the creation of antihydrogen.
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        In atomic physics, scattering studies using beams of positrons
and positronium with speeds comparable to those of atomic electrons are contributing
to the unravelling of general collision phenomena as well as illuminating specific
interactions and processes such as exchange and annihilation.
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