Potassium 40 argon 40 dating
Mechanical crushing is also a technique capable of releasing argon from a single sample in multiple steps.
Laser probes also allow multiple ages to be determined on a single sample aliquot, but do so using accurate and precise spatial control.
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.
J value uncertainty can be minimized by constraining the geometry of the standard relative to the unknown, both vertically and horizontally.
The NMGRL does this by irradiating samples in machined aluminum disks where standards and unknowns alternate every other position.
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.
These reactor produced isotopes of argon must be corrected for in order to determine an accurate age.
Therefore, unlike the conventional K/Ar technique, absolute abundances need not be measured.
The quantity of potassium in a rock or mineral is variable proportional to the amount of silica present.