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Geophysics, Lecture Notes- Physics - Prof Gavin Bell 6

Geophysics, Lecture Notes- Physics - Prof Gavin Bell 6 -...

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PX266 Geophysics (2010/11) Lecture 4 Handout – Radiometric Dating Dr. Gavin Bell A summary of some radiometrically useful decay systems. The variables N , D , R and T ½ are used in the lecture notes. The 14 C to 14 N half-life (by beta decay) is only about 5700 years: too short for geology but good for archaeology. Parent ( N ) Daughter ( D ) Nonradiogenic ( R ) T ½ (Ma) Carbon-14 Nitrogen-14 Carbon-12 0.00573 Samarium-147 Neodymium-143 Neodymium-144 106000 Potassium-40 Argon-40 Argon-36 11850 Rubidium-87 Strontium-87 Strontium-86 48800 Uranium-235 Lead-207 Lead-204 704 Uranium-238 Lead-206 Lead-204 4468 Thorium-232 Lead-208 Lead-204 14010 Radiocarbon dating – short exercise during the lecture A sample of a leather strap from this helmet is obtained, trying to prevent any contamination of it by atmospheric carbon, fingers, plastic tools/bags, etc. It is analysed in an accelerator mass spectrometer where the 14 C / 12 C ratio is found to be 8.7×10 -13 ± 3%. Is the helmet Viking, mediaeval or modern?
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Radiocarbon dating – background Cosmic rays generate 14
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