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Curtin University
Oklo Fossil Reactors

Things to do and think about

Not all the answers are available on these pages (try searching the web yourself to find the answers).

  1. When did the Oklo reactors start operating and for how long did the reactors operate?
  2. How did scientists determine the age and operating period of the fossil reactors?
  3. What are three of the longest lived fission products produced by the natural fossil reactors and what are their half lives?
  4. What two major biological events took place prior to and contributed to the formation of the natural reactors.
  5. How long can man made fission reactors generate energy for without refuelling and why does this differ substantially from the Oklo fossil reactors?
  6. What fraction of the long lived fission products (137Cs, 129I and 107Pd) are present at Oklo today?
  7. Using a 50m ball of string mark out on the string the;
    • beginning and end of the various eras, periods and epochs of the geological calendar.
    • start and stop times for the natural fossil reactors
    • half lives of the long lived fission products produced by the fossil reactors.
    • How many centimetres from the end does man appear on the string
  8. Using a large sheet of paper (newspaper is fine), cut the paper in half to represent a half life;
    • How many times can you cut the paper in half?
    • After ten half lives (cuts), what fraction of the paper do you have left?
    • Use the paper and ‘cut in half method’ – what fraction of 239Pu will be left after one 137Cs Half life?
    • If fission product A decays radioactively twice as fast as fission product B and there is 10 times more of A than B, when will there be equal amounts of A and B?
  9. Repeat the same experiment as described in number 8 using a long piece of string or a known volume (eg large soft drink bottle or container) of water.
  10. What are the mass numbers, halflives and biological effects of the long lived radioisotope of Cs, Pd, Pu, I and Tc?

If you get stuck or you are curious to find out more email the author (Dr Robert Loss) at: r.loss@curtin.edu.au