KArArAr

KArArAr refers to a radiometric dating technique that is a refinement of the traditional K-Ar dating method and the Ar-Ar dating approach. It uses neutron irradiation to convert a stable isotope of potassium (39K) into argon-39, creating an internal tracer that allows precise measurement of the potassium content and the radiogenic argon produced over time. The resulting 40Ar*/39Ar ratio provides an age, with the irradiation yield serving as a calibration reference.

Principle and how it works: Potassium-40 decays to argon-40 as part of its natural decay chain. In Ar-Ar techniques, an artificial source of argon is introduced by irradiating the sample to convert 39K to 39Ar. By measuring the released argon isotopes (39Ar and 40Ar) from the sample, scientists determine the amount of potassium and the amount of radiogenic argon that has accumulated since cooling or solidification. Stepwise heating or laser-assisted release yields an age spectrum that can be interpreted through well-established dating models.

Procedure and data interpretation: Samples are irradiated in a nuclear reactor to produce 39Ar from potassium. The sample is then outgassed in an ultrahigh vacuum, and argon isotopes are measured by mass spectrometry. By releasing argon in steps, a plateau or isochron age can be determined, and age is calculated from the ratio of radiogenic 40Ar* to the produced 39Ar, with corrections for any excess argon or atmospheric contamination.

Applications and limitations: KArArAr dating is widely used to date volcanic rocks, minerals such as sanidine and plagioclase, and other geologic materials from the Quaternary to Precambrian. It offers high precision and internal checks but requires access to irradiation facilities and careful calibration. Potential sources of error include argon loss, excess argon, and perturbations during irradiation.

See also: K-Ar dating, Ar-Ar dating, radiometric dating.