Radioactive Fallout
In the 1930s, scientists found that bombarding uranium metal with neutrons caused the nuclei of uranium atoms to break apart, or fission. One significant feature of this reaction was that very large amounts of energy were released during nuclear fission. The first practical application of this discovery was the atomic bomb, developed by scientists working in the United States in the early 1940s.
The atomic bomb takes advantage of the energy released during fission to bring about massive destruction of property and human life. However, every bomb blast is also accompanied by another event known as radioactive fallout. The term radioactive fallout refers to all radioactive dust and particles that fall to the earth after a nuclear explosion. This combination of dust and particles contains hundreds of isotopes formed when a uranium nucleus fissions. Iodine-131 and yttrium-98 are only two of the many isotopes that are formed during an atomic bomb blast.
When these isotopes are formed, they come together as only very small particles. The force of the blast assures that large particles will not survive. In this form, the radioactive dust and particles may remain suspended in air for days, weeks, or months. Only when they have consolidated to form larger particles will they fall back to Earth.
Once they have reached the earth, these particles face different fates. Some isotopes formed during fission have very short half-lives. They will decay rapidly and pose little or no environmental threat. Others have longer half-lives and may remain in the environment for many years.
The components of radioactive fallout that cause the greatest concern are those that can take some role in plant or animal metabolism. For example, the element strontium is chemically similar to the element calcium. Strontium can replace calcium in many biochemical reactions. That explains why the following scenario is so troubling.
Strontium-90 released during a fission bomb blast falls to the earth, coats grass, and is eaten by cows. The cows incorporate strontium-90 into their milk, just as they do calcium. When growing children drink that milk, the strontium-90 is used to build bones and teeth, just as calcium is. Once incorporated into bones and teeth, however, the radioactive strontium continues to emit harmful radiation for many years.
The dangers of radioactive fallout are one of the major reasons that the United States and the former Soviet Union were able to agree in 1963 on a limited ban of nuclear weapons testing. In that agreement, both nations promised to stop nuclear weapons testing in the atmosphere, under water, and in outer space.
Half-Life; Radioactive Decay; Radioactivity
Resources
Books
Inglis, D. R. Nuclear Energy: Its Physics and Social Challenge. Reading, MA: Addison-Wesley, 1973.
Jagger, J. The Nuclear Lion: What Every Citizen Should Know About Nuclear Power and Nuclear War. New York: Plenum, 1991.
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