NANTeL Radiation Worker Training Practice Test

Alpha radiation consists of heavy, positively charged particles that are highly ionizing but have very short range in matter. Because of their size and charge, they lose energy quickly and cannot travel far; a sheet of paper or a few layers of clothing can stop them, and they pose little external threat. However, if alpha-emitting material is inhaled or ingested, these particles can deposit in the lungs or other organs, delivering a concentrated dose to nearby tissues.

That description matches the statement that alpha radiation has low penetrating power, is shielded by simple barriers like paper or clothing, and is hazardous if inhaled or ingested. The other ideas—being highly penetrating and requiring heavy shielding, posing no hazard at all, or traveling long distances in air—do not fit alpha radiation’s actual behavior.