alpha particle
a stable particle having the same bound configuration of 2 protons and 2 neutrons as a helium-4 nucleus and emitted during a nuclear disintegration
GRM: n.
Note: by extension, any helium-4 nucleus
References:
GEN elementary particle
GEN fundamental particle
SEE neutron
SEE alpha radiation
SEE proton
SEE alpha rays

ENERGY TERM COURTESY OF ENERGY.EU