Radioactivity

1. Radioactivity

2. 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 Food

3. http://www.youtube.com/watch?v=UvN54Jo7Cs8 http://www.youtube.com/watch?v=VzdqZtf-Sz4

4. Background radiation is higher in some places than in others, it depends where you are on the Earth’s surface. • Suggest three possible ways radiation could get into the air. • Try to identify areas of high radioactivity.  ?

5. Safety first There are several types of radiation. They differ in what effects they have and their nature. All radioactive sources must be handled safely. Do you know what the hazard symbol for radiation is?

6. Alpha radiation -  Description: 2 neutrons, 2 protons (helium nuclei) Electric Charge: +2 Relative Atomic Mass: 4 Penetration power: Stopped by paper or a few cm of air Ionisation effect: Strongly ionising Effects of Magnetic/Electric Field: Weakly deflected Helium nuclei

7. Beta radiation -  Description: High energy electron Electric Charge: -1 Relative Atomic Mass: 1/1860th Penetration power: Stopped by few mm of aluminium Ionisation effect: Weakly ionising Effects of Magnetic/Electric Field: Strongly deflected high energy electron

8. Gamma radiation -  Description: High energy electromagnetic radiation Electric Charge: 0 Relative Atomic Mass: 0 Penetration power: Reducedby several cm’s of lead or several metres of concrete Ionisation effect: Very weakly ionising Effects of Magnetic/Electric Field: NO deflection Electromagnetic radiation

9. The penetration power of the three types of radiation.    Skin or paper stops ALPHA Thin aluminium stops BETA Thick lead reduces GAMMA Thin mica

10. The effects of a field on radiation Beta radiation has a –1 charge and a small mass so 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 is only weakly deflected. The effect of a magnetic or electric field on radiation depends upon the nature of the radiation.

11. a decay - involves strong and coloumbic forces - alpha particle and daughter nucleus have equal and opposite momentums (i.e. daughter experiences “recoil”)

12.  decay - three types 1) - decay - converts one neutron into a proton and electron - no change of A, but different element - release of anti-neutrino (no charge, no mass) 2) + decay - converts one proton into a neutron and electron - no change of A, but different element - release of neutrino 3) Electron capture

13. g decay - conversion of strong to coulombic E - no change of A or Z (element) - release of photon - usually occurs in conjunction with other decay

14. radioactive – nucleus which spontaneously decomposes forming a different nucleus and producing one or more particles nuclear equation – shows the radioactive decomposition of an element A. Radioactive Decay

15. Alpha-particle production Alpha particle – helium nucleus Examples A. Radioactive Decay • Types of Radioactive Decay • Net effect is loss of 4 in mass number and loss of 2 in atomic number.

16. Beta-particle production A. Radioactive Decay • Types of Radioactive Decay • Beta particle – electron • Examples • Net effect is to change a neutron to a proton.

17. Gamma ray release A. Radioactive Decay • Types of Radioactive Decay • Gamma ray – high energy photon • Examples • Net effect is no change in mass number or atomic number.

18. Positron production A. Radioactive Decay • Types of Radioactive Decay • Positron – particle with same mass as an electron but with a positive charge • Examples • Net effect is to change a proton to a neutron.

19. Electron capture A. Radioactive Decay • Types of Radioactive Decay • Example

20. Using your results from the previous three investigations, fill in the table below: least medium most shortest medium longest least medium most most medium least yes yes no

21. Match the radiation Electromagnetic radiation Stopped by paper or skin Alpha High energy electron Reduced by lead Beta Helium nuclei Gamma Stopped by aluminium

22. Ionising radiation What happens if radiation is incident upon a living cell? Radiation can ionise 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 ionising radiation, gamma is the least. Ionising radiation can be used to kill cancer cells.

23. Ionisation questions • What is ionisation? • How is a neutral atom positively ionised? • How is a neutral atom negatively ionised? • What two effects on living cells can ionisation have? • Which type of radiation is the most ionising? • Which type of radiation is the least ionising? When a neutral atom loses or gains electrons and hence charge. By losing electrons. By gaining electrons. Kill cells or cause cancer. Alpha radiation. Gamma radiation.

24. Which type of radiation is….. • The most penetrating? • The least penetrating? • Least dangerous outside the body? • Most dangerous inside the body? • High energy electrons? • Has a negative charge? • Is weakly ionising? • Has zero charge and zero mass? • Only reduced in intensity by lead and concrete? Gamma Alpha Alpha Alpha Beta Beta Beta Gamma Gamma

25. Uses of radiation

26. Sterilisation 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 sterilisation. Gamma Source unsterilised sterilised

27. Radiotherapy A carefully controlled beam of gamma rays can be used to kill cancer cells. It must be directed carefully to minimise the damage to normal cells. However, some damage is unavoidable and this can make the patient ill. It is therefore a balancing act - getting the dose high enough to kill the cancerous cells, but as low as possible to minimise the harm to the patient.

28. Leak detection in pipes The radioactive isotope is injected into the pipe. Then the outside of the pipe is checked with a Geiger-Muller 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. GM tube The isotope must have a short half life so the material does not become a long term problem. 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.

29. Thickness Control Mill 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. 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: plastics, paper, sheet steel. Beta Source detector Hydraulic ram Electronic instructions to adjust rollers.

30. Detecting radiation What are the different methods? Gieger-Muller Tube Spark counter Photographic film Cloud chamber

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

32. Geiger-Muller Tube 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. Good at detecting alpha and beta, not as good at detecting gamma. collision & ionisation The Argon contains a little bromine to act as a quenching agent and prevent continuous discharge. radiation Argon gas Argon gas mica window When the radioactivity enters the tube, it ionises the gas in the tube. This produces a pulse of current which is amplified and passed to a counter. counter 124 125

33. The Spark Detector The 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 ionising radiation is placed close to the detector there is a marked increasing in the amount of sparking. Which type of radiation will be detected the best? Why? High voltage supply

34. Cloud chamber Cloud chambers show the actual paths of the ionising particles. They rely on ionisation. The cloud chamber is cooled and then is super-saturated with alcohol. If an ion is formed a droplet of condensation appears. Best for alpha radiation as alpha most ionising; then Beta which shows faint traces, but cloud chambers are not as good for gamma as gamma is only weakly ionising. Cooled alcohol vapour Radioactive source Solid carbon dioxide

35. Alpha Beta Gamma X rays Which type of radiation is the most penetrating? 

36. Alpha Beta Gamma X rays Which type of radiation is the most damaging inside the body? 

37. Alpha Beta Gamma X rays Which type of radiation is the most dangerous outside the body? 

38. Pre-natal scans Radiotherapy Smoke detectors Detecting leaks Which of the following is not a use of radiation? 

39. Radioactive Decay Radioactive elements are unstable. They decay, change, into different elements over time. Here are some facts to remember: The half-life of an element is the time it takes for half of the material you started with to decay. Remember, it doesn’t matter how much you start with. After 1 half-life, half of it will have decayed. Each element has it’s own half-life ( page 1 of your reference table) Each element decays into a new element (see page 1) C14 decays into N14 while U238 decays into Pb206 (lead), etc. The half-life of each element is constant. It’s like a clock keeping perfect time. Now let’s see how we can use half-life to determine the age of a rock or other artifact.

40. The grid below represents a quantity of C14. Each time you click, one half-life goes by. Try it! C14 – blueN14 - red As we begin notice that no time has gone by and that 100% of the material is C14

41. The grid below represents a quantity of C14. Each time you click, one half-life goes by. Try it! C14 – blueN14 - red After 1 half-life (5700 years), 50% of the C14 has decayed into N14. The ratio of C14 to N14 is 1:1. There are equal amounts of the 2 elements.

42. The grid below represents a quantity of C14. Each time you click, one half-life goes by. Try it! C14 – blueN14 - red Now 2 half-lives have gone by for a total of 11,400 years. Half of the C14 that was present at the end of half-life #1 has now decayed to N14. Notice the C:N ratio. It will be useful later.

43. The grid below represents a quantity of C14. Each time you click, one half-life goes by. Try it! C14 – blueN14 - red After 3 half-lives (17,100 years) only 12.5% of the original C14 remains. For each half-life period half of the material present decays. And again, notice the ratio, 1:7

44. Element X (Blue) decays into Element Y (red) The half life of element X is 2000 years. How old is our sample? See if this helps: 1 HL = 1:1 ratio 2 HL = 1:3 3 HL = 1:7 4 HL = 1:15 If you said that the sample was 8,000 years old, you understand radioactive dating. If you’re unsure and want an explanation just click.

45. Element X (blue) Element Y (red) How old is our sample? We know that the sample was originally 100% element X. There are three questions: First: What is the X:Yratio now? Second: How many half-lives had to go by to reach this ratio? Third: How many years does this number of half-lives represent? 1) There is 1 blue square and 15 red squares. Count them. This is a 1:15 ratio. 2) As seen in the list on the previous slide, 4 half-lives must go by in order to reach a 1:15 ratio. 3) Since the half life of element X is 2,000 years, four half-lives would be 4 x 2,000 or 8,000 years. This is the age of the sample.