Which statement best describes radiation sickness?

• A. It is caused by exposure to low levels of radiation over many years
• B. It occurs only in people working with radioactive materials
• C. It is caused by radiation entering the body
• D. It is caused by massive amounts of external exposure

Answer: (D)

Radiation sickness happens when the whole body is hit by a very large dose of ionizing radiation in a short time. The key factor is how big and how fast that dose is. This illness is most reliably caused by external exposure—radiation coming from outside the body, such as from a nuclear accident or a very high-dose exposure to X-rays or gamma rays.

Low-level exposure over years tends to cause cancers and other late effects, not the acute illness described by radiation sickness. Internal contamination (radiation inside the body, from ingested or inhaled materials) can contribute to illness if the dose is high, but the defining feature of radiation sickness as tested here is a massive external dose delivered quickly.