P4 - Uses of radioactive isotopes

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  • Created by: Naomi
  • Created on: 21-01-13 19:56
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  • Uses of radioisotopes
    • Background radiation
      • Background radiation is due to:
        • Radioactive substances present in rocks (especially granite) and soil
        • Cosmic rays from space
        • Man-made sources including radioactive waste from industry and hospitals
      • Most background radiation is from natural sources, but some is from human activity
    • Smoke detectors
      • A smoke detector contains an isotope which emits aplha particles
        • Alpha is used because it is very ionising and won't get out of the smoke alarm
      • Without smoke, the alpha particles will ionise the air which creates a tiny circuit that can be detected by the circuit in the smoke alarm
        • With smoke, the alpha particles are partially blocked, so there is less ionisation of the air. The resulting change in current is detected and the alarm sounds
      • The isotope needs to have a long half life so it can last a long time without needing to be replaced
    • Dating rocks
      • Some rock types such as granite contain traces of uranium, a radioactive material
        • The uranium isotopes present in the rocks go through a series of decays, eventually forming a stable isotope of lead
        • By comparing the amounts of uranium and lead present in a rock sample, its approximate age can be found
          • The proportion of lead increases as time increases
            • After one half life half of it is unchanged, and the other half has changed into lead
              • After 2 half lives 1/4 of the uranium is left and 3/4 has changed into lead



Very useful :)  5*

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