In the graph above, the count rate drops from 80 to 40 counts a minute in two days, so the half-life is two days.In the next two days, it drops from 40 to 20 - it halves.Radiometric dating or radioactive dating is a technique used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed.The method compares the abundance of a naturally occurring radioactive isotope within the material to the abundance of its decay products, which form at a known constant rate of decay.and is now the principal source of information about the absolute age of rocks and other geological features, including the age of fossilized life forms or the age of the Earth itself, and can also be used to date a wide range of natural and man-made materials.Together with stratigraphic principles, radiometric dating methods are used in geochronology to establish the geological time scale.But it is possible to measure how long it takes for half the nuclei of a piece of radioactive material to decay.This is called the half-life of the radioactive isotope.
The graph shows the decay curve for a radioactive substance.Alpha particles are made of 2 protons and 2 neutrons.This means that they have a charge of 2, and a mass of 4 (the mass is measured in "atomic mass units", where each proton & neutron=1) We can write them as , or, because they're the same as a helium nucleus, . They have a low penetrating power - you can stop them with just a sheet of paper.This means that beta particles are the same as an electron. Gamma rays have a high penetrating power - it takes a thick sheet of metal such as lead, or concrete to reduce them significantly.We can write them as or, because they're the same as an electron, . Beta particles have a medium penetrating power - they are stopped by a sheet of aluminium or plastics such as perspex. Gamma rays do not directly ionise other atoms, although they may cause atoms to emit other particles which will then cause ionisation.