The older a particular radioactive material, the radiation it emits. In fact it takes the same amount of time for the activity (decays per second) to fall by whatever the start value. This length of time is known as the half life. This is because there is a 50:50 chance that a particular nuclei will decay in each half life period. This means that the more radioactive nuclei there are, each with a chance of decaying in each half life, the the activity will be. Therefore the half life is also the time it takes for the number of parent atoms in a sample to .
This is because there is a 50:50 chance that a particular nuclei will decay in each half life period. This means that the more radioactive nuclei there are, each with a chance of decaying in each half life, the the activity will be. Therefore the half life is also the time it takes for the number of parent atoms in a sample to .
Therefore the half life is also the time it takes for the number of parent atoms in a sample to .
This idea can be used to date materials. Uranium isotopes, which have a very long half-life, decay via a series of relatively short-lived radioisotopes to produce stable isotopes of lead. The relative proportions of uranium and lead isotopes in a sample of igneous rock can, therefore, be used to date the rock. The proportions of the radioisotope potassium-40 and its stable decay product argon can also be used to date igneous rocks from which the gaseous argon has been unable to escape.
It is more accurate to use a computer to measure and plot the activity. This is espcially true when dealing with isotopes with a very long half life. Even then the results of radioactive dating contain significant uncertainties and we must be careful not to be too precise with our calculations.
