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WJEC GCSE Additional Science Teacher’s Notes 6. Explain what safety precautions a specialist radiotherapy nurse would have to take if treating a patient using external beam radiotherapy. The safety precautions are: leave the room when the gamma beam is on observe patient through lead glass screen focus the beam carefully control beam exposure so dose is effective but minimised. 7. Which radioisotopes would you use for leak detection Gamma emitter with a short half-life is needed – technicium-99. 8. Why is it important that radiosotopes used in leak detection have short half-lives Half-life must be short to ensure that the dose received by the general public and the operators is very small. 9. Why are beta sources used for thickness control applications The intensity of beta particles passing through the paper will be affected by the thickness of the paper. No alpha particles would get through even the thinnest paper, and gamma rays would be unaffected by the paper. 10. State with a reason which radioisotope you would choose for use in a thickness control machine. How would you arrange this source under the sheet Strontium-90 would be a good source for a thickness detector as it is a beta emitter with a suitable half-life where the intensity of the beta particle beam would not change significantly from day to day. The source would be extended underneath and across the full width of the paper so that the detector sampled the full width. 11. Why is it important that the Geiger counter is long enough to stretch across the whole sheet The Geiger counter needs to sample across the whole of the width of the sheet to ensure it is an even thickness. 12. Which radioisotopes would you use for metal weld detection Explain your answer. A gamma emitter with a long half-life so that the gamma beam intensity did not change significantly from day-to-day – Europium-152 or Barium-133. 13. What precautions would the operator need to take when analysing a metal weld Keep (very small) source in sealed lead container when not in use Minimise time in use Collimate beam (so it only goes in one direction) Stand away from the beam when in use Ensure no other people are in the way of the beam Wear lead apron/tabard 14. Why would α and β radioisotopes be unsuitable for this application Alpha and beta radiation would not penetrate through the weld. 75
WJEC GCSE Additional Science Teacher’s Notes 15. Explain which radioisotopes you could use for a machine that sterilises medical instruments. A gamma emitter with a long half-life so that the gamma beam intensity did not change significantly from day-to-day – Europium-152 or Barium-133. 16. Why is it important that the sterilising machine is surrounded by a thick lead shield To minimise dose/exposure to the operators. 17. Explain why americium-241 would be a good choice for the radioisotope in a smoke detector. It is an alpha emitter with a long half-life so that the beam intensity does not drop significantly from day-to-day. 18. Why doesn’t a smoke alarm need a lead shield around it It is an alpha emitter and so the alpha particles are absorbed inside the detector by the walls of the radioactive source holder and the plastic cover. Discussion point Some types of food are treated in the same way. Strawberries, onions, potatoes and spices can all be sterilised in this way. By killing the bacteria on the food products they can have a substantially longer shelf-life. Would you like to eat irradiated strawberries An interesting discussion pitting scientific understanding against irrational fear! 76
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