When the health and safety of an entire population is at risk following a nuclear-related accident, radioprotection has to be taken to a different dimension. What specific measures can be taken when large amounts of radioactive matter are released into the atmosphere?
The ability to provide adequate protection depends on an understanding of the risks involved. The catastrophic events that occurred at the Chernobyl reactor in 1986 have taught us a tragic lesson on how to ensure the security of a population. The smaller incident at the Mayak reactor in the Urals (1957), as well as the Three Mile Island (1979) and Tokaimura (2000) accidents have also served as wake-up calls, though the latter two fortunately did not release any radioactive waste. Experience has also been accumulated from the bombs dropped on Hiroshima and Nagasaki and the nuclear bomb tests that continued throughout the 50s and 60s – though these were conducted in principle far from inhabited areas.
The threats posed immediately after a nuclear explosion or a nuclear accident depend on the elapsed time. Seconds after the event has occurred, short-lived elements predominate over a very small area near the bomb impact or the accident. Over time, the most active elements blown into the atmosphere have had time to dissipate, the longer-lived elements take over. They are less radioactive but can spread the radiation over large areas.
The main risks of exposure are posed by the radioactive cloud, the inhalation of radioisotopes in the air, and deposits of radioactive elements in the ground as well as in sources of food and water. The main worry is that the exposure humans feel will be an internal as well as an external phenomenon.
The main cause of external exposure is the gamma photons which can penetrate hundreds of meters of atmosphere before being absorbed. They originate from the radioactive cloud formed at the moment of the explosion, and can also be emitted from radioactive deposits on the ground. The internal exposure is caused by the inhalation and ingestion of active radioactive substances that vanishes in a few days or weeks after the release, primarily iodine 131 which attaches itself to the thyroid gland.
As with natural catastrophes, simple yet effective measures can prevent the more serious consequences. Possible actions range from evacuation and sheltering of populations to the careful monitoring of food and drink made available in the regions of concern.