| 1. | Physics. a concentrated stream of particles, as electrons, neutrons, or protons, generated for studying particle interactions, nuclear structure, crystal structure, etc. |
| 2. | Military. a high-energy stream of such particles for use as a weapon or for antimissile defense. |
| particle beam n. A beam of atoms or subatomic particles that have been accelerated by a particle accelerating device, aimed by magnets, and focused by a lens. |