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Analysis of Natural Thermoluminescence in Type 4 Chondrites

Analysis of Natural Thermoluminescence in Type 4 Chondrites. Overview. Natural Thermoluminescence (TL) Terrestrial Age Thermal History High Natural TL → Low Terrestrial Age Low Natural TL → High Terrestrial Age / Recent Reheating. Overview. Total of 15 Samples

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Analysis of Natural Thermoluminescence in Type 4 Chondrites

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  1. Analysis of Natural Thermoluminescence in Type 4 Chondrites

  2. Overview • Natural Thermoluminescence (TL) • Terrestrial Age • Thermal History • High Natural TL → Low Terrestrial Age • Low Natural TL→ High Terrestrial Age / Recent Reheating

  3. Overview • Total of 15 Samples • Antarctic, Non-Antarctic, Observed Falls • For Each Sample • Ran 3 Pans • 3 Natural Curves, 9 Induced Curves per Sample • Determined peak heights at 250°C and 400°C for both types of curves

  4. Data Reduction • Two Methods (both in krad) • Equivalent Dose = Ratio of natural peak height to induced peak height at a given glow curve temperature (250ºC) multiplied by test dose (0.75) • Natural TL = EXP[2.303 * (1.2903 * LOG(Ratio) + 1.089)] • Ratio = (natural peak height at 250ºC / natural peak height at 400ºC)

  5. Equivalent Dose

  6. General Results • 15 Samples Ran • 11 Different Meteorites • Wide Spread Among Data • Antarctic Samples – Low Natural TL • Observed Falls – High Natural TL • Non-Antarctic Samples – Span Low to High

  7. General Results

  8. Observed Falls • 6 Samples • 4 Different Meteorites • Albareto (1766), Bovedy (2)(1969), BoXian (1977), Cali (2)(2007) • Albareto, BoXian, Cali – Results Typical • Bovedy – Natural TL is very low • Some Possibilities: • Samples recently reheated in some way (like shock reheating) • Not Bovedy • Sounds of Bovedy

  9. Observed Falls

  10. Antarctic Meteorites • 5 Samples • 3 Different Meteorites • Most Exhibit Low Levels of Natural TL • WIS 91618 shows higher natural TL levels than others • Possible Reasons: • Recent, but unobserved fall • Exposed to more than typical amounts of radiation

  11. Antarctic Meteorites

  12. Non-Antarctic Meteorites • 10 Samples • 8 Different Meteorites • Includes both Observed Falls (like Cali, bottom left, and Bovedy, top right) and finds (like Julesburg, bottom right)

  13. Non-Antarctic Meteorites

  14. Comparison With Other Data • Hasan et al: data from Antarctic meteorites • Benoit and Sears: data from Antarctic meteorite believed to have been a recent fall • Our data mostly falls within the range set by both, as is expected

  15. Conclusions • Results confirm relationships between terrestrial age and natural TL intensity • Observed falls → High natural TL → Low terrestrial age • Antarctic finds → Low natural TL → High terrestrial age • Some exceptions • Observed falls → Bovedy • Antarctic finds → WIS 91618, 16 and 17

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