Natural Thermoluminescence Projects
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Terrestrial
history of meteorite finds using bulk natural TL
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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.
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Terrestrial
history of meteorite finds using fusion crust natural TL
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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.
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Unusual
irradiation/thermal histories
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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
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Mineralogically/petrographically
unusual meteorites
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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.
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Anomalous
fading and TL characterization
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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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