Having just read the outstanding biography of the great physicist who predicted the existence of the positron (The Strangest Man: The Hidden Life of Paul Dirac, Mystic of the Atom) and having also recently tried to digest the Wiki article on Positron Emission Tomography (PET scanning), I have a couple of basic questions about positron/electron interactions.
Question 1 - when a positron and an electron encounter each other, they are annihilated and photons are emitted (i.e. radiation). Is the frequency of this radiation the same for all positron/electron collision-annihilations? Or does it depend on the energy of the positron/electron pair at the moment of their encounter (or maybe something else)?
Question 2 - how “close” to each other do the positron and electron have to be in order to interact and annihilate? Or does their “successful” interaction depend on factors other than their distance from each other, e.g. angle of approach, their momentum, etc.?