It can’t be used to determine the age of a moon rock or a meteorite.For nonliving substances, scientists use other isotopes, such as potassium-40.The Carbon-14 within a living organism is continually decaying, but as the organism is continuously absorbing Carbon-14 throughout its life the ratio of Carbon-14 to Carbon-12 atoms in the organism is the same as the ratio in the atmosphere.Once an organism dies it stops taking in Carbon in any form.The rule is that a sample is safe when its radioactivity has dropped below detection limits. So, if radioactive iodine-131 (which has a half-life of 8 days) is injected into the body to treat thyroid cancer, it’ll be “gone” in 10 half-lives, or 80 days.This stuff is important to know when using radioactive isotopes as medical tracers, which are taken into the body to allow doctors to trace a pathway or find a blockage, or in cancer treatments.As long as an organism is alive, the amount of C-14 in its cellular structure remains constant.
A useful application of half-lives is radioactive dating.It might take a millisecond, or it might take a century. But if you have a large enough sample, a pattern begins to emerge.It takes a certain amount of time for half the atoms in a sample to decay.The unstable Carbon-14 within the organism begins to decay to form Nitrogen-14 by emitting a beta particle.Over time there is a gradual decrease in the amount of Carbon-14 and the ratio of Carbon-14 atoms to other Carbon atoms declines. Therefore half of the Carbon-14 has decayed after 5730 years.They need to be active long enough to treat the condition, but they should also have a short enough half-life so that they don’t injure healthy cells and organs.Radioactive dating is helpful for figuring out the age of ancient things.The Executive Board, various Committee Members, and countless volunteers ensured that all attendees experienced the professionalism and training they deserve and have come to expect from the CSDIAI.There are far too many individuals to personally thank by name, but just know that all efforts were noticed and extremely appreciated.This decay is an example of an exponential decay, shown in the figure below.Knowing about half-lives is important because it enables you to determine when a sample of radioactive material is safe to handle.