How far can beta particles travel in the air?

• A. 1 meter
• B. 2 meters
• C. 5 meters
• D. 10 meters

Answer: (B)

Beta particles are fast electrons emitted by certain radioactive decays. In air they interact with air molecules and lose energy mainly through ionization, so their range is limited. For most beta emitters you encounter, a practical travel distance in air is about two meters. This makes two meters the best fit among the options, since one meter is generally a bit short for many beta sources, while five or ten meters would apply only to exceptionally high-energy betas not typical in standard environmental health settings. Beta is more penetrating than alpha radiation but far less than gamma radiation, which helps explain why its travel in air is confined to a few meters rather than many.