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Positron Annihilation Experiments

Because they annihilate with electrons, positrons are often used to probe materials in positron annihilation experiments:

1. a positron is emitted from a source (this starts a timer),
(Usually the source is an artificially produced isotope, such as sodium-22, which emits positrons through inverse beta decay.)

2. enters a material,

3. finds an electron (perhaps forms Ps),

4. and is annihilated,

5. emitting two photons (which stop the timer)

This annihilation time is very important, for it tells you about the material structure. Remember how it is easier for "pick-off" annihilation to occur when there are a lot of electrons around? This means that if the positron is sent somewhere in the material with a lot of electrons, the annihilation time will be very short.