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The Common Denominator in Archeological Dating

The Common Denominator in Archeological Dating. Arthur C. Lucas, Sc.D. Nextep Technologies, Inc. Oklahoma State University. Luminescence Dosimetry. Archeological Dating Geological Dating Personal Dosimetry. Primary Natural Sources of Dose in Solids. Uranium Thorium Potassium

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The Common Denominator in Archeological Dating

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  1. The Common DenominatorinArcheological Dating Arthur C. Lucas, Sc.D. Nextep Technologies, Inc. Oklahoma State University

  2. Luminescence Dosimetry Archeological Dating Geological Dating Personal Dosimetry

  3. Primary Natural Sources of Dose in Solids • Uranium • Thorium • Potassium • Cosmic Radiations

  4. Methods for assay of soils Gamma Ray Spectroscopy Beta Ray Spectroscopy Thick Sample Alpha Spectroscopy

  5. Primary Sources of BackgroundMeasurement Uncertainty • Radioactivity in the Detector • Radioactivity in the Detector Shell • Environmental Background Level • Geometrical Effects

  6. Dose in Rad from observation of the sample Age in years = Dose Rate in situ, Rad/annum

  7. Regenerative Dose Determination

  8. Additive Dose Determination

  9. Thick Sample AlphaSpectroscopy The thick sample method adds accuracy and sensitivity to alpha spectroscopy

  10. In an infinite isotropic medium with included alpha activity:

  11.  =  S/Eo

  12.  is the specific activity of the sample in Bq/gm Z is the ADC zero in MeV L is the lower level for analysis in MeV e is the geometrical efficiency of the detector A is the area of the detector in cm2 T is the counting time in seconds S is the stopping power in MeV cm2/gm E is the energy of the particle counted in MeV E0 is the initial kinetic energy of the alpha particle in MeV N is the number of counts in an energy bin (4)

  13. Historical Personnel Dosimeter Issue Initially the dosimeter was bonded by kasil - about 30 mR per month

  14. Historical PersonnelDosimeter Issue When the kasil was removed potassium in the glass shell remained. -About 3 mR/month

  15. Historical PersonnelDosimeter Issue When the dosimeter was designed with low potassium glass the background was reduced to the internal dose in the solid only. The problem was reduced to chemical purification of the starting material. -approximately 0.3 mR/month

  16. Verification of Internal Dose in the material • The internal dose was verified by thick sample alpha spectroscopy. To do this a special method of handling the spectra was developed which yielded specific activity directly.

  17. Summary • The creation of low intrinsic radioactivity dosimeters requires an absolute zero test capability. • The certification of materials for construction of spectrometers would greatly aid in assay of terrestrial materials.

  18. Outline of Dating Issues Dating Equation Example of Dose Determination LET Dependence Alpha/Beta Sensitivities Am-241/Sr-90 Nuclides in the Natural Chains Thorium Uranium Potassium Gamma Spectroscopy Ge Na*(Tl) Alpha Spectroscopy Thick Sample Geometries

  19. Personal Dosimetry Example materials LiF CaF2 Al2o3 Li2B4O7 Background Examples Potassium U/Th Surrounding Materials Example Backgrounds. Beta Rays from included Materiasl .01 to 20 mR/day Cosmic Ray Background .05 mR/day

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