When nuclear accidents happen, many people imagine radiation spreading everywhere and lasting forever. The reality is more complex. Radioactive materials move, change and sometimes disappear faster than people expect.

The Chernobyl accident in 1986 and the Fukushima Daiichi accident in 2011 released radioactive materials into the air, soil and water around those two nuclear power plants. The general term for the materials that got released is “radionuclides.”

Some decayed quickly, effectively disappearing without having done much harm. But others, mostly isotopes of iodine, cesium, strontium and plutonium, remained in the environment for many years, damaging human health and the environment. The mechanisms by which they do that damage depends on the material itself, the weather and the local environment. For example, cesium chemically behaves like sodium and potassium, which are accumulated in human tissues. Strontium chemically behaves like calcium, which is accumulated in bones.

As a nuclear engineer and researcher who has worked on tracking radiation levels and exposure in projects related to Chernobyl, Fukushima Daiichi, and U.S. Department of Energy national laboratories and nuclear sites, I have seen how science and engineering help measure, map and manage radiation to keep people safe. I study how radionuclides migrate because this helps predict where radioactive contamination goes, how fast it moves, and who or what might be exposed over time.

The most important lesson is that radiation risk can be understood and controlled. Human senses can’t detect radiation, but scientific instruments can accurately measure the amounts and types of radiation in an area. Once it is measured, scientists and engineers can make informed decisions about how to use well-established methods and modern technology to reduce risk.

How radioactivity travels

The major nuclear accidents at Chernobyl and Fukushima Daiichi released radioactive materials into the atmosphere as tiny particles. Winds carried these particles across countries and even between continents. Rain and snow brought........

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