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KS4 Physics
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  1. KS4 Physics Radioactivity

  2. Contents Radioactivity Background radiation Safety rules Types of radiation Uses of radiation Summary activities

  3. Background radiation Background radiationis the radiation all around us. Working in pairs try to think of five possible sources of background radiation. You have FIVE minutes! Rocks Air Building materials Outer space (cosmic) Food

  4. Background radiation The sources of radiation for a particular location are shown: a) Draw a pie chart of this data. b) Which source of radiation is the largest? c) Suggest three possible ways radiation could get into the air. d) Find out about areas of high radioactivity.

  5. Marie Curie Marie Curie was a famous scientist. • Try to find out about her life: • When and where did she live? • What work did she do? • What problems did she have to overcome? • Which famous prizes was she awarded?

  6. Contents Radioactivity Background radiation Safety rules Types of radiation Uses of radiation Summary activities

  7. Safety first There are several types of radiation. They differ in their effects and physical nature. All radioactive sources must be handled safely. Do you know what the hazard symbol for radiation is? As well as the normal laboratory safety instructions you follow are there any extra rules concerning radioactivity?

  8. Safety rules 1. Do not handle radioactive sources directly; use tongs or a robotic arm. 2. Never point a radioactive source at a fellow worker or yourself. 3. Store radioactive sources in lead-lined containers when not in use. 4. Always wear radiation protection suits. 5. Radiation badges should be worn to record exposure to radiation. Task:Working in pairs choose three of the safety rules that would be most relevant in your school and explain why you chose them. Also say which safety rule you think is the most important and why.

  9. Contents Radioactivity Background radiation Safety rules Types of radiation Uses of radiation Summary activities

  10. Range of radiation investigation Use three sources of radiation: alpha, beta and gamma. • Measure the background radiation reading using a radiation detector. • For each source separately, using tongs, move the source slowly away from the radiation detector until the reading on the detector is the same as that for background radiation. This is the range of the radiation. Record your results. • Questions: • Name three possible sources of the background radiation you recorded. • Which type of radiation had the shortest range? • Which type of radiation would be most dangerous 10m away from you? Why?

  11. Penetrating power investigation Use three sources of radiation: alpha, beta and gamma. • Measure the background radiation reading using a radiation detector. • For each source separately, using tongs, place a piece of paper in between the detector and the source and then record the reading. Repeat this with a sheet of aluminium and again with a sheet of lead. Record your results. • Questions: • Which type of radiation was the least penetrating? • Which type of radiation would be most dangerous outside your body? Why? • Which type of radiation would be most dangerous inside your body? Why?

  12. Penetrating power of the three types of radiation    Thinaluminiumstops beta Thin mica Skin orpaper stopsalpha Thick lead reduces gamma

  13. Match the radiation electromagnetic radiation stopped by paper or skin alpha High-energy electron reduced by lead beta helium nuclei gamma stopped by aluminium

  14. Magnetic field investigation Use three sources of radiation: alpha, beta and gamma. • Measure the background radiation reading using a radiation detector. • For each source separately, using tongs, place a magnet in between the detector and the source and then record the reading. Record your results. • Questions: • Which types of radiation were affected by the magnetic field? • Which type of radiation was not affected by the magnetic field? • Beta radiation is high-energy electrons. TVs use electrons. Why should you not put your hi-fi loudspeakers too close to your TV?

  15. The effects of field on radiation The effect of a magnetic or electric field on radiation depends upon the type of radiation. Beta radiation has a –1 charge and a small mass so it is strongly deflected. + Gamma radiation has no mass or charge so it is not deflected. – Alpha radiation has a +2 charge but a RAM of 4 so it is only weakly deflected.

  16. Results table medium least most shortest medium longest least medium most most least medium yes yes no

  17. Alpha (α) radiation helium nuclei Description: 2 neutrons, 2 protons Electric charge: +2 Relative atomic mass: 4 Penetration power: Stopped by paper or a few cm of air Ionization effect: Strongly ionizing Effects of magnetic/electric field: Weakly deflected

  18. Beta (β) radiation high-energy electron Description: High-energy electron Electric charge: -1 Relative atomic mass: 1/1860 Penetration power: Stopped by a few mm of aluminium Ionization effect: Weakly ionizing Effects of magnetic/electric field: Strongly deflected

  19. Gamma () radiation electromagnetic radiation Description: High-energy electromagnetic radiation Electric charge: 0 Relative atomic mass: 0 Penetration power: Reduced by several cms of lead or several metres of concrete Ionization effect: Very weakly ionizing Effects of magnetic/electric field: Not deflected

  20. Ionizing radiation What happens to living cells when exposed to radiation? Radiation can ionize cells, which causes cellular damage. If the exposure is high it can kill the cell. If the exposure is lower it can cause cancer. The higher the exposure, the higher the risk of cancer. Alpha is the most ionizing radiation; gamma the least ionizing. Ionizing radiation can be used to kill cancer cells.

  21. Contents Radioactivity Background radiation Safety rules Types of radiation Uses of radiation Summary activities

  22. Uses of radiation

  23. Sterilization gammasource unsterilized sterilized Gamma rays are used to kill bacteria, mould and insects in food. This can be done even after the food has been packaged. It can affect the taste, but supermarkets like it because it lengthens the shelf life. Gamma rays are also used to kill bacteria on hospital equipment. It is particularly useful with plastic equipment that would be damaged by heat sterilization.

  24. Radiotherapy A carefully controlled beam ofgamma rayscan be used tokill cancer cells. It must be directed carefully to minimize the damage to normal cells. However, some damage is unavoidable and this can make the patient ill. It is therefore abalancing act–getting the dose high enough to kill the cancerous cells, but as low as possible to minimize the harm to the patient.

  25. Leak detection in pipes A radioactive isotope is injected into the pipe. Then the outside of the pipe is checked with a Geiger-Müller detector, to find areas of high radioactivity. These are the points where the pipe is leaking. This is useful for underground pipes that are hard to get near. The isotope must have a short half-life so the material does not become a long-term problem. GM tube The radioactive isotope must be a gamma emitter so that it can be detected through the metal and the earth where the pipe leaks. Alpha and beta rays would be blocked by the metal and the earth.

  26. Thickness control mill If not enough radioactivity is detected then the rollers compress to make the material thinner. This method is used in the manufacture of lots of sheet materials, such as plastics, paper and sheet steel. A radioactive source is on one side of the material and a detector on the other. If too much radioactivity is getting through, then the material is too thin and the rollers open up a bit to make the material thicker. beta source detector hydraulic ram Electronic instructions to adjust rollers.

  27. Detecting radiation What are the different methods of detecting radiation? Geiger-Müller tube spark counter photographic film cloud chamber

  28. Photographic film 1. What happens to film when it is exposed to radiation? It darkens. 2. Can photographic film tell you the type of radiation that it has been exposed to? No, just the amount of radiation received. 3. What can this be used for? Can be used in radiation badges, which record the exposure of workers to radiation. Different windows on the badge detect different types of radiation.

  29. Geiger-Müller tube collision & ionization radiation The detector is a metal tube filled with gas. The tube has a thin wire down the middle and a voltage between the wire and the casing. It is good at detecting alpha and beta radiation, but not as good at detecting gamma radiation. argon gas mica window When the radioactivity enters the tube, it ionizes the gas in the tube. This produces a pulse of current, which is amplified and passed to a counter. counter 125 124

  30. Spark detector high-voltage supply A spark detector consists of a metal grid and a metal strip. A high voltage is applied between the grid and the strip. The voltage is increased until electrical arcing (sparking) across the gap just occurs. When ionizing radiation is placed close to the detector there is a marked increase in the amount of sparking. Which type of radiation will be detected most easily? Why?

  31. Cloud chamber Cloud chambers show the actual paths of the ionizing particles. They rely on ionization. The cloud chamber is cooled and is then super-saturated with alcohol. When an ion is formed a droplet of condensation appears. Cloud chambers are good for showing alpha radiation as this is the most ionizing. Beta radiation shows faint traces. Cloud chambers are not good for showing gamma radiation, as it is only weakly ionizing. radioactivesource cooledalcoholvapour solid carbon dioxide

  32. Contents Radioactivity Background radiation Safety rules Types of radiation Uses of radiation Summary activities

  33. Glossary • alpha radiation –Positively charged particles made up of two protons and two neutrons. It is the least penetrating of the three main types of radiation. • background radiation –Constant low-level radiation from food and environmental sources. • beta radiation – High-energy electronsemitted by some radioactive materials. It is more penetrating than alpha radiation but less penetrating than gamma radiation. • cloud chamber – A device that shows the paths of ionizing particles. It is good at detecting alpha radiation. • gamma radiation – Short wavelength electromagnetic radiation emitted during radioactive decay. It is the most penetrating of the three main types of radiation. • Geiger-Müller tube –A device used to detect and measure radiation from radioactive materials. • ionizing radiation – High-energy radiation capable of ionizing substances through which it passes.

  34. Anagrams

  35. Multiple-choice quiz