Radioisotope Dating by yurtgc548


									Radioisotope Dating
       What is radioactivity?
• Radioactivity is the spontaneous emission
  of energy from unstable atoms.
• There are stable atoms, which remain the
  same forever, and unstable atoms, which
  break down or 'decay' into new atoms.
• These unstable atoms are said to be
  'radioactive', because they emit
  radioactivity from the nucleus as they
        What is radioactivity?
• Radioactivity is a random process that
  happens naturally as the isotopes in
  particular elements decay.
• The isotopes continue to break down over
  – The length of time that is taken for half of the
    nuclei in an element to decay is called its
        What is the connection with
           exponential decay?
• The radioactive half-life for
  a given radioisotope is the
  time for half the
  radioactive nuclei in any
  sample to undergo
  radioactive decay.
• After two half-lives, there
  will be one fourth the
  original sample, after three
  half-lives one eight the
  original sample, and so
  Dating the Dead Sea Scrolls
• We date the Dead Sea Scrolls which have
  about 78% of the normally occurring
  amount of Carbon 14 in them.
• Carbon 14 decays at a rate of about
  1.202% per 100 years
        Years after
                          % Carbon remaining
                      0                        100
                  100     =B2-0.01202*B2
  Dating the Dead Sea Scrolls
• Do excel example
    Dating the Dead Sea Scrolls

• We find that the Dead Sea Scrolls would
  date from between 2100 to 2000 years
• Current estimates are that a 95%
  confidence interval for their date is 150 BC
  to 5 BC.

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