What is an isotope?
Everyone is familiar with every-day elements such as copper, gold, silver, oxygen, and carbon. What is less familiar to many people is that of the 118 known elements, many—indeed most—have several isotopes. For example, carbon has 14 different isotopes. Not all of them occur in nature; some need to be made. But all of them are the element carbon. Whichever isotope of carbon is under consideration, its nucleus always has 6 positively charged protons. If the element has 1 proton, then it is hydrogen. If it has 92, then it is uranium.
What makes one isotope of an element different from another is the number of neutrons in the nucleus. Unlike protons, neutrons have no charge, and the number of neutrons in the nucleus may vary and still be the same element. For example, most carbon has 6 neutrons and is stable. But some naturally-occurring carbon has 8 neutrons. It's known as carbon-14 and is radioactive.
Isotopes, therefore, are atoms of an element that have the same number of protons but different numbers of neutrons. That can make all the difference in the world. Some isotopes are stable, that is, they do not decay, and have an infinitely long shelf life. Others are unstable and undergo radioactive decay whereby they transform themselves into other, ultimately stable isotopes. As they decay, they may emit different forms of radiation such as gamma rays, x-rays, electrons, and alpha particles, depending on the isotope and how it decays. For many isotopes, the emitted radiation has useful properties.
Isotopes are used for hundreds of vital research, development, biomedical, and industrial applications that benefit society every day. For example, germanium-68 is used to calibrate positron emission tomography scanners widely used in the diagnosis of cancer. Rhenium-188 is used to prevent arterial blockage following heart surgery. Actinium-225 is an alpha emitter that has been shown to be effective in the treatment of certain kinds of cancer. Various stable isotopes of calcium are used in human nutrition studies. And nickel-63 is used in electron capture detectors that help locate explosives for homeland security.
These isotopes and many others are produced and distributed by the Department of Energy's Isotope Program to the industrial, research, and medical communities both domestically and worldwide. Click on the pie chart to learn more about how isotopes are used.
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