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Table 15.5 “Some Radioactive Isotopes with Medical Applications” lists several radioactive isotopes and their medical uses.

For instance, leaks in underground water pipes can be discovered by running some tritium-containing water through the pipes and then using a Geiger counter to locate any radioactive tritium subsequently present in the ground around the pipes.(Recall that tritium is a radioactive isotope of hydrogen.) Tracers can also be used to follow the steps of a complex chemical reaction.Shroud of Turin In 1989, several groups of scientists used carbon-14 dating to demonstrate that the Shroud of Turin was only 600–700 y.Many people still cling to a different notion, despite the scientific evidence.Technetium-99 can also be used to test thyroid function.

Bones, the heart, the brain, the liver, the lungs, and many other organs can be imaged in similar ways by using the appropriate radioactive isotope.

Radioactive isotopes have a variety of applications.

Generally, however, they are useful because either we can detect their radioactivity or we can use the energy they release.

The half-life of radioactive isotopes is unaffected by any environmental factors, so the isotope acts like an internal clock.

For example, if a rock is analyzed and is found to contain a certain amount of uranium-235 and a certain amount of its daughter isotope, we can conclude that a certain fraction of the original uranium-235 has radioactively decayed.

Using such methods, scientists determined that the age of the Shroud of Turin (Figure 15.3 “Shroud of Turin”; purported by some to be the burial cloth of Jesus Christ and composed of flax fibres, a type of plant) is about 600–700 y, not 2,000 y as claimed by some.