Atoms with the same number of protons but different number of neutrons are called isotopes. Each element found in nature is a mixture of isotopes. The most common atomic mass for carbon is twelve: six protons and six neutrons. Carbon-thirteen is the rarest isotope of carbon with six protons and seven neutrons. Carbon-fourteen is used to help determine the age of relics; this is called radiocarbon dating.
All living things absorb carbon dioxide from the air as long as they live, taking in all three isotopes of carbon. After death the carbon-fourteen atoms disintegrate at a known rate; the carbon-twelve atoms do not disintegrate. The age of the relics are calculated by comparing the ratio of carbon-fourteen atoms to carbon-twelve atoms. Carbon-fourteen has a half-life of 5,700 years. Since half of the carbon-fourteen atoms disintegrate every 5,700 years, radiocarbon dating cannot be used for relics over 35,000 years old. The age of some rocks can be determined by measuring the amount of radioactive argon gas they contain; this is called potassium-argon dating. Potassium-forty emits argon-forty as it disintegrates. The age of the oldest human bones have been determined using potassium-argon dating.
Radioactive isotopes are useful tools in medicine. Some radioactive isotopes are used to treat cancer. Cobalt-sixty kills rapidly dividing cancer cells and has a half-life of five years. Iodine-131 can also be used to treat an over active thyroid or to kill thyroid cancer cells. Tracer isotopes are used to find medical abnormalities. Tracer iodine-131 is used to diagnose thyroid disease. Tracer technetium-99 is used to locate thyroid, kidney, and brain tumors. Tracer phosphorus-32 is used to find bone cancers and to treat skin cancer. Isotopes are used in medical imaging devices. Common imaging isotopes are: rubidium-87 and thallium-203. Other medical radioisotopes include: cesium-137, chromium-51, cobalt-48, hydrogen-three or tritium, gold-198, iridium-192, iron-59, sodium-24, strontium-85 and strontium-90, xenon-133, and yttrium-90.
Radioactive isotopes can be used to determine whether a painting is authentic. Isotopes are used in oil and gas pipelines to label the start of a new shipment. Isotopes have been used to study the wear of engine parts and to study how fertilizers are used most efficiently in agriculture. Americium-241 is used in smoke detectors because it can detect early stage fires. Isotopes are used in homeland security scanners to detect explosives. Isotopes are used in mining to monitor the height of coal in hoppers and to determine the structural integrity of dams, pipe welds, aircraft, ships, and bridges (Iridium-192).
