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 Cosmic Radiations
Methods for assay of soils Gamma Ray Spectroscopy Beta Ray Spectroscopy Thick Sample Alpha Spectroscopy
Primary Sources of Background Measurement Uncertainty Radioactivity in the Detector Radioactivity in the Detector Shell Environmental Background Level Geometrical Effects
Age in years = Dose in Rad from observation of the sample Dose Rate in situ, Rad/annum
Regenerative Dose Determination
Additive Dose Determination
Thick Sample Alpha Spectroscopy The thick sample method adds accuracy and sensitivity to alpha spectroscopy
In an infinite isotropic medium with included alpha activity:
= S/Eo
(4) 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
Historical Personnel Dosimeter Issue Initially the dosimeter was bonded by kasil - about 30 mR per month
Historical Personnel Dosimeter Issue When the kasil was removed potassium in the glass shell remained. -About 3 mR/month
Historical Personnel Dosimeter 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
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.
Summary 1.The creation of low intrinsic radioactivity dosimeters requires an absolute zero test capability. 2.The certification of materials for construction of spectrometers would greatly aid in assay of terrestrial materials.
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
Personal Dosimetry Example materials LiF CaF 2 Al 2 o 3 Li 2 B 4 O 7 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