Exposure to radiation can occur in many ways. For those radioactive elements that decay via release of gamma rays, one can be exposed simply by being near the radiation. This is because the external gamma rays can travel through air. However, not all radioactive elements release gamma rays. For those other radioactive elements that decay via release of alpha or beta particles, one has to inhale or ingest the radioactive substance in order to be exposed. For that type of radiation, exposure could occur only via inhalation of vapors or of small soil particles containing radioactive material, incidental ingestion of soil contaminated with radioactive material, and ingestion of water contaminated with radioactive material.