In positron decay, a proton-rich nucleus emits a positron (positrons are antiparticles of electrons and have the same mass as electrons but positive electric charge), thereby reducing the nuclear charge by one unit. In this case, the process can be represented by: An annihilation occurs when a low-energy positron collides with a low-energy electron.
Electron capture, which is also typical for proton-rich nuclei, competes with positive beta decay, which is more common for lighter nuclei. Electron capture is the primary decay mode for isotopes with insufficient energy (Q < 2 x 511 keV) difference between the isotope and its prospective daughter for the nuclide to decay by emitting a positron. On the other hand, electron capture is always an alternative decay mode for radioactive isotopes with sufficient energy to decay by positron emission.
The coulomb forces that constitute the major mechanism of energy loss for electrons are present for either positive or negative charge on the particle and constitute the major mechanism of energy loss for positrons. Whether the interaction involves a repulsive or attractive force between the incident particle and orbital electron (or atomic nucleus), the impulse and energy transfer for particles of equal mass are about the same. Therefore positrons interact similarly with the matter when they are energetic. The track of positrons in a material is similar to the track of electrons; even their specific energy loss and range are about the same for equal initial energies.
At the end of their path, positrons differ significantly from electrons. When a positron (antimatter particle) comes to rest, it interacts with an electron (matter particle), resulting in the annihilation of both particles and the complete conversion of their rest mass to pure energy (according to the E=mc2 formula) in the form of two oppositely directed 0.511 MeV gamma rays (photons).
See also: Positron Interaction
See also: Shielding of Positrons