What is the primary risk factor of alpha particles when they enter the body?

Alpha particles primarily pose an internal hazard when they enter the body due to their high mass and charge, which gives them a limited ability to penetrate materials, including human skin. Because they can be stopped easily by a sheet of paper or the outer layer of skin, the primary concern arises when they are ingested or inhaled. Once inside the body, alpha particles can then interact with biological tissues and cells, causing significant damage to them on a molecular level.

This internal exposure is the main reason alpha radiation is classified as a serious health risk. The energy released by alpha particles can lead to ionization of nearby atoms and molecules, which can damage DNA and result in various health issues, including cancer. This differentiates the risk associated with alpha particles from other forms of radiation that might cause harm primarily through external exposure or other pathways.