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  • Created by: Jadii
  • Created on: 11-11-13 20:22
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  • Isotopes
    • Atoms of the same element which have different mass numbers (different number of neutrons)
    • Relative Isotopic Masses
      • Take abundances into account
        • Cl-35 and Cl-37
          • 75% and 25%
      • (35x75) + (37x25) / 100 = 35.5
    • Half-life of radioisotope carbon-14 is 5730 years
      • After two half -lives it will be 25% of the original count rate
        • As 1 half-life is 5730 years, the time taken for the radioisotope to decay to 25% of its original value is 2 x 5730 years = 11460 years
    • A cautionary note
      • For radiometric systems to work as geological clocks there are some criteria that must be fulfilled:
        • The half-life of the radioisotope must be known accurately
        • There must have been no movement of either parent or daughter isotopes out or into a mineral since the time  of crystaliiation of the rock
          • There must have been no resetting of the radiometric clock - heating and deformation of rocks


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