Certified Safety Professional Practice Exam

Alpha radiation poses no known external radiation hazard primarily due to its inability to penetrate the outer layers of human skin. Alpha particles are relatively large and positively charged, and when emitted from a radioactive source, they can be stopped by a piece of paper or even the outer layer of the skin. This means that while alpha radiation can be harmful if ingested or inhaled, it does not pose a risk when exposure occurs externally.

In contrast, beta radiation, x-ray radiation, and neutron radiation can penetrate human tissue to varying degrees, presenting potential hazards when exposure occurs from outside the body. Beta particles can penetrate skin and cause harm if sufficient energy is involved, while x-rays are a form of electromagnetic radiation that can pass through soft tissue and potentially cause damage to internal organs. Neutrons, due to their uncharged nature, can also pass through matter, leading to a broad range of biological effects when interacting with biological tissues.

Therefore, the unique characteristics of alpha radiation, particularly its inability to penetrate the skin and its limited range in air, distinguish it as the type of radiation that does not present a known external hazard.