The leptons also fall into two distinct groups.
Charge: -1 0
electron electron neutrino
muon muon neutrino
tau tau neutrino
In the table, the lightest particles are at the top, the heavier ones below. The electron and all neutrinos are believed to be stable particles. Each particle in the first column has a neutrino partner in the second column. The antimatter equivalents of the electron, muon and tau all carry a single positive charge, but all the neutrinos and antineutrinos are neutral. Compared to the quarks and their composites, all the leptons have relatively low masses (Greek leptos = light, small); some of the neutrinos possibly have no mass.
TRIUMF creates intense beams of both negative and positive (i.e. antimatter) muons, 1/9 of a proton mass, which decay rapidly, usually into electrons or positrons (i.e. anti-electrons) and neutrinos. Many radioisotopes made at TRIUMF are powerful emitters of positrons, and are used in the PET brain scanner.