Natural Thermoluminescence Projects

Terrestrial history of meteorite finds using bulk natural TL

Bulk natural TL can also be used to determine the amount of time a meteorite found in Antarctica has spent on the ice surface. This information in conjunction with terrestrial ages derived from cosmogenic radionuclides can provide insight into the relative importance of direct meteorite infall onto the ice surface and transportation of meteorites within the ice to the collection sites. These types of comparisons can indicate the stability of ice fields. The natural TL of suites of meteorites from hot deserts has similar implications, although "gaps" in the TL/terrestrial age record are indicative of meteorite loss through erosion rather than ice movements.

Terrestrial history of meteorite finds using fusion crust natural TL

One of the primary limitations in the quantitative determination of terrestrial/surface exposure ages from natural TL levels is the range of TL in modern fall. The lack of a single equilibration value imposes a significant degree of uncertainty in age estimates. Our group is studying the natural TL of fusion crust in an attempt to over come this problem. The natural TL in the first few mm from the outer surface of a meteorite is completely drained during atmospheric passage. Natural TL should rebuild in this outer layer as a function of time due to terrestrial radiation dose. In order to calculate a terrestrial age the annual dose of radiation received by the meteorite must be known. This can be calculated using formulas which predict the muon dose, however, our research group plans to send several dosimeters to Antarctica which will directly measure the annual dose.

Unusual irradiation/thermal histories

About 15% of all meteorites in all collections exhibit either relatively high or low natural TL levels. The natural TL data indicate that these meteorites have experienced a thermal or irradiation history considerably different from that of "normal" meteorites. Meteorites with very high natural TL levels must have experienced little or no heating and/or a high radiation dose over the last 10,000 years or so of their orbital history. Low natural TL levels can be produced by "reheating" (either by impact processing or by solar heating at perihelia

Mineralogically/petrographically unusual meteorites

Our group also continues to search the TL database for heavily shocked meteorites and applying TL data for the subclassification of meteorites as part of the ongoing TL survey of newly recovered Antarctic meteorites.

Anomalous fading and TL characterization

The interpretation of natural TL data requires some knowledge of the basic TL properties of meteorites. Natural TL is commonly used to date events in the lifetime of meteorites. Therefore, it is important to determine if anomalous fading (the unusually rapid loss of TL as a function of time after irradiation) is occurring. Our group is also characterizing the TL properties of fusion crust samples from ordinary chondrites and weathering products, primarily sulfates and carbonates, that might potentially contaminate fusion crust samples. If these minerals have significant TL sensitivity they will have to be removed prior to TL analysis.


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