Parameters for a number of neutron irradiations are examined and results intercompared for the Bjurböle meteorite; data for the 1967 Valecitos-1 irradiation are presented.
Apparent I-Xe ‘formation’ ages are reproducible for three different samples of Bjurböle, suggesting isotopic homogeneity for initial iodine in the bulk material.
I reflects the iodine isotopic ratio at closure of the host mineral.
Most iodine hosts are secondary minerals so the I–Xe system is unique in providing details of post-formational chronometry not readily available with other chronometers.The short half-life of I gives it exceptional precision.However, the secondary nature of iodine host minerals, combined with the inherent precision of I–Xe, were responsible for a large database of “whole-rock” I–Xe ages that were not easily interpreted.As this problem evolved historically, doubts were cast upon the viability of the I–Xe system as a chronometer which persisted until it was tested against other chronometers in single-mineral systems.Properly calibrated, absolute I–Xe ages reflect the true closure time of the host minerals, and sequences of closure times in different hosts provide cooling rates for the parent object.
Two inclusions from the Allende meteorite exhibit multiple I-Xe isochrons corresponding to an age difference of 3.7 ± 1.5 m.y.
I when Shallowater began retaining xenon is the same within experimental error as the ratio in 10 chondrites previously measured, indicating that Shallowater and these chondrites began to retain xenon simultaneously to within one or two million years.
Calculated values of the formation interval for these bodies lie between 60 and 220 million years depending on the model for nucleosynthesis assumed.
We report the results of Xe analyses of the eucrites Bereba, Cachari, Caldera, Camel Donga, Chervony Kut, Ibitira, Jonzac, Juvinas, Milbillillie, Moore County, Padvarninkai, Pasamonte, Pomozdino, Sioux County, and Vetluga, and the howardite Petersburg.
The obtained data together with data from the literature were utilized for the calculation of PuXe ages using a modified method where the concentration of the reference element Nd (that is used in the traditional PuXe dating) is replaced by that of spallation Xe is calculated via the Ba/REE ratios that are very similar in different samples of a given meteorite.
In comparison with the traditional PuXe dating the present method avoids problems of sampling heterogeneity and uncertainties in absolute instrument sensitivity and can be used when the concentration of Nd in a sample is not known.