A technician handles two different radioactive sources. One source emits alpha radiation and the other emits gamma radiation. The technician is standing one metre away from each source. Explain why the gamma source presents the greater radiation hazard to the technician at this distance, while the alpha source would present the greater hazard if the technician accidentally swallowed it.

Alpha particles have a very short range in air (a few centimetres) and are stopped by a sheet of paper or the technician’s clothing, so from one metre away they cannot reach the technician.

Gamma rays are highly penetrating and can travel large distances through air, so at one metre they can reach the technician and deposit energy in his tissues.

If the alpha source is swallowed, the alpha particles are emitted inside the body where they are highly ionising and can damage cells and tissues directly.

Gamma rays are weakly ionising and, when inside the body, they pass through with little interaction, causing less damage than alpha particles would if ingested.