Ar-39-Ar-40 dating method: Control of possible Ar-39 loss due to neutron irradiation of sample

A geochronologic study of three basalt samples from the Central American trench (Pacific Ocean) was performed by means of K-Ar and Ar-39-Ar-40 techniques. The data show discrepancies due to a loss of neutron-induced Ar-39 isotope during irradiation of the samples with fast neutrons in a nuclear reactor. The Ar-39-Ar-40 investigation of basalts in which potassium is concentrated in a fine-grained cryptocrystalline phase confirms flat a risk exists of obtaining faulty data due to neutron irradiation. A control procedure of eventual losses in neutron-induced isotope is proposed that is based on isotope dilution with a Ar-38 tracer during the analysis of both initial (unexposed) sample and those exposed to fast neutrons.