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However, effects related to grain size may be significant in the interpretation of apatites from sediments which have been heated to paleotemperatures within the He PRZ, as grains of different radii will give different ages for a particular thermal history. The effects of long alpha-stopping distances on (U-Th)/He ages.

While this has yet to be demonstrated in natural samples, this holds considerable promise for obtaining more precise thermal history control in sedimentary basins. Ken Farley of Caltech, based on the systematics presented in Farley (2000) and references therein, allows modelling of the (U-Th)/He age expected from any inputted thermal history, in grains of any specified radius.

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Detailed experimental measurements at Caltech have led to further refinements in understanding the diffusion systematics of Helium in apatite (Farley, 2000).

This work, focussed on the much-studied Durango apatite, has suggested that diffusion systematics are controlled by the physical grain size.

Klíčovou roli v setkání však hrají první minuty, potažmo dokonce vteřiny. Často vás tak může svádět družit se spíše s těmi, které už znáte, nebo v čase pro networking kontrolovat e-maily a sociální sítě na svém telefonu. Zkuste si ze začátku vytyčit cíl, s kolika novými lidmi se seznámíte.A number of subsequent applications of the method (e.g. (Uranium thorium)/helium dating of apatite: experience with samples from different geochemical environments. House et al., 1997; Warnock et al., 1997; Wolf et al., 1997) have illustrated the potential of the technique to provide useful thermochronometric information at temperatures less than 100C. Chemical Geology (Isotope Geoscience Section), 112, 179-191. However, due to a number of factors, outlined in the following Sections, a (U-Th)/He age must be interpreted carefully before the true meaning of the measured age can be evaluated. m), a significant proportion of alpha particles produced with an apatite grain may be emitted from the grain, resulting in loss of radiogenic helium. (1996) showed how this effect can be corrected for, by calculation of a correction factor (known as F Calculations of Helium retention over geological timescales, based on laboratory diffusion measurements, suggest that Helium is progressively lost at temperatures between 40 and 90C (for timescales of tens of millions of years), with this temperature range constituting a Helium “ Partial Retention Zone” or He PRZ.

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