What is potassium argon dating used for
Ar total fusion measures ratios, making it ideal for samples known to be very argon retentive (eg. Total fusion is performed using a laser and results are commonly plotted on probability distribution diagrams or ideograms.
In order for an age to be calculated by the Ar technique, the J parameter must be known.
The quantity of potassium in a rock or mineral is variable proportional to the amount of silica present.
Therefore, mafic rocks and minerals often contain less potassium than an equal amount of silicic rock or mineral.
However, because each of these parameters is difficult to determine independantly, a mineral standard, or monitor, of known age is irradiated with the samples of unknown age.
The monitor flux can then be extrapolated to the samples, thereby determining their flux.
This flux is known as the 'J' and can be determined by the following equation: As the table above illustrates, several "undesirable" reactions occur on isotopes present within every geologic sample.
The results from a laser probe can be plotted in several graphical ways, including a map of a grain showing lateral argon distribution.
Ca F is also routinely irradiated and measured to determine the Ar technique relies on ratios instead of absolute quantities, we are able to extract and measure multiple aliquots of argon from a single sample.
Multiple argon extractions can be performed on a sample in several ways.
The monitoring of the interfering reactions is performed through the use of laboratory salts and glasses.
For example, to determine the amount of reactor produced Ar ratio of the glass is then measured in the mass spectrometer to determine the correction factor that must be applied to the rest of the samples in that irradiation.