Which type of natural radiation has the most massive particles: alpha, beta, or gamma?
Alpha particles have the largest mass.
Alpha particles are the giants among radiation particles. These particles consist of 2 neutrons and 2 protons i.e. the nucleus of a Helium atom. The mass of an alpha particle is 4 amu (atomic mass unit). Beta particles are subatomic particles (like an electron but originating from the nucleus) and thus much smaller, they have a mass of approximately 0.0005 amu. Gamma radiation is electromagnetic radiation, these are waves not particles and therefore have no mass at all.
NB: 1 amu =