What is the primary hazard of alpha radiation in terms of body exposure?

The primary hazard of alpha radiation in terms of body exposure is that it produces significant ionisation internally. Alpha particles are heavy, positively charged particles that do not penetrate the skin effectively; they can be stopped by a sheet of paper or even the outer layer of human skin. However, if alpha-emitting materials are ingested or inhaled, they can cause intense ionisation in nearby cells due to their high energy and mass. This dense ionisation can lead to significant cellular damage, increasing the risk of cancer and other health issues.

While it is true that alpha radiation cannot penetrate the skin and thus does not cause direct external damage, internal exposure from alpha particles is particularly harmful due to their ability to ionise biological tissues. This is why precautions need to be taken to avoid inhalation or ingestion of alpha-emitting substances, despite their relative safety in terms of external exposure.