sentence: Hospitals only have equipment to detect gamma rays.
sentences_before: Unlike most common radiation sources, polonium-210 emits only alpha particles. These do not penetrate even a sheet of paper or human skin. Thus they are invisible to normal radiation detectors.
sentences_after: Both gamma rays and alpha particles are classified as ionizing radiation, and can cause radiation sickness.
concept_name: hospital
headings: Alexander Litvinenko How the poison works
categories: 1962 births 2006 deaths Russian writers