The isotopes the KAr system relies on are Potassium (K) and Argon (Ar).
Potassium, an alkali metal, the Earth's eighth most abundant element is common in many rocks and rock-forming minerals.
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.
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.
This imprecision (and inaccuracy) is transferred to the secondary minerals used daily by the Ar age equation will become continually more refined allowing much more accurate and precise ages to be determined.
Because this (primary) standard ultimately cannot be determined by Ar, it must be first determined by another isotopic dating method.
Argon loss occurs when radiogenic K by a fast neutron reaction) can be used as a proxy for potassium.
Therefore, unlike the conventional K/Ar technique, absolute abundances need not be measured.
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.