Types of radioactive dating methods
The Potassium-Argon dating method is the measurement of the accumulation of Argon in a mineral.It is based on the occurrence of a small fixed amount of the radioisotope Ar with a half-life of about 1,300 million years.Any material which is composed of carbon may be dated.Herein lies the true advantage of the radiocarbon method.If the rock containing these minerals is heated, the tracks will begin to disappear.If the rock is heated high enough, 120C for apatite, all tracks will disappear.
Potassium is a component in many common minerals and can be used to determine the ages of igneous and metamorphic rocks.
By measuring the C concentration or residual radioactivity of a sample whose age is not known, it is possible to obtain the number of decay events per gram of Carbon.
By comparing this with modern levels of activity (1890 wood corrected for decay to 1950 AD) and using the measured half-life it becomes possible to calculate a date for the death of the sample. As a result of atomic bomb usage, C ages of objects younger than 1950.
This half-life (t 1/2) is the name given to this value which Libby measured at 556830 years. After 10 half-lives, there is a very small amount of radioactive carbon present in a sample.
At about 50 000 to 60 000 years, the limit of the technique is reached (beyond this time, other radiometric techniques must be used for dating).
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The New Zealand physicist Ernest Rutherford, suggested in 1905 that the exact age of a rock could be measured by means of radioactivity.