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, H, is a radioactive isotope of hydrogen.) Tracers can also be used to follow the steps of a complex chemical reaction.
Table 11.5 "Some Radioactive Isotopes That Have Medical Applications" lists several radioactive isotopes and their medical uses.
A tiny amount of carbon-14 is produced naturally in the upper reaches of the atmosphere, and living things incorporate some of it into their tissues, building up to a constant, although very low, level.
Once a living thing dies, however, it no longer acquires carbon-14, and as time passes, the carbon-14 that was in the tissues decays.
After incorporating radioactive atoms into reactant molecules, scientists can track where the atoms go by following their radioactivity.
One excellent example of this is the use of radioactive carbon-14 to determine the steps involved in the photosynthesis in plants.
If a once-living artifact is discovered and analyzed many years after its death, with the remaining carbon-14 compared to the known constant level, an approximate age of the artifact can be determined.