Potassiu m argon dating
Argon loss occurs when radiogenic K by a fast neutron reaction) can be used as a proxy for potassium.
For the J to be determined, a standard of known age must be irradiated with the samples of unknown age.
Because this (primary) standard ultimately cannot be determined by Ar, it must be first determined by another isotopic dating method.
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.
Potassium can be mobilized into or out of a rock or mineral through alteration processes.