Mesons

**Definition:** Short-lived elementary particles found in cosmic radiation or produced from nuclear disintegration. Their mass is between that of protons and electrons and they can be negative, positive, or neutral. pi-Mesons (pions) are heavier than mu-mesons (muons) and are proposed for cancer radiotherapy because their capture and disintegration by matter produces powerful, but short-lived, secondary radiation.

**Tree numbers:** - G01.249.600