Application of xenon isotopes for dating pitchblende (cas 1317-99-3)s

Add time:08/16/2019    Source:sciencedirect.com

Twenty pitchblendes have been dated by the Xes−Xn spectrum technique. Most of the ages obtained are in good agreement with ages obtained by the UPb isotopic technique. Age spectra of these samples have the typical “step up”-form. When the Xes−Xen and UPb ages are discordant, age spectra are complex. Mixing of mineral associations with different ages is also typical for these samples. When galena and molybdenite are present in pitchblendes, the Xes−Xen method gives true ages, in contrast to the UPb method. There is a qualitative correlation between the release-kinetics of radiogenic Xe and the degree of discordance between Xes−Xn and UPb ages.We have also used a method based on the decay of 129I produced in induced fission of 235U by natural neutrons monitored with 136XeN. In this case the age is a function of the 129Xe136XeN ratio only. The method does not require stepwise annealing and yields the real age even for 50% loss of radiogenic Xe.During the investigation we have found Xe with large excesses of isotopes 134, 132 and 131. This isotopic composition cannot be explained by a mixture of Xes with Xen It seems to be caused by the migration of radioactive precursors of Xe.Xe with the distorted isotope composition is released from the samples at low temperatures and does not affect the age calculated from a high-temperature plateau.

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