During the 1950s and early 1960s, the U.S. Government conducted about one hundred nuclear weapons tests in the atmosphere at a test site in Nevada. Depending upon their location, people living in the U.S. at that time were exposed to varying levels of radiation, notably from Iodine-131 (I-131). The I-131 dose/risk calculator (entitled "Radioactive I-131 from Fallout") is a tool that allows any individual to estimate his or her radiation exposure to I-131 from the Nevada nuclear weapons tests and to estimate fallout-related risks of developing thyroid cancer. Use the I-131 Calculator. For more general information, read Get the Facts About Exposure to I-131 Radiation.