Nuclear and Atomic Physics

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  • 1. Nuclear Physics
  • 2. Shortcut to AtomicBombTest
  • 3. RADIATION ELECTROMAGNETIC RADIATION NUCLEAR RADIATION RADIO LIGHT IR UV X ray ALPHA particles BETA particles GAMMA rays
  • 4. Using Nuclear Radiation
  • 5. Cancer Therapy
  • 6. Electricity Production
  • 7. Smoke Detectors
  • 8. Sterilisation
  • 9. Radiocarbon Dating
  • 10. Radioactive Tracers
  • 11. Thickness Monitoring
  • 12. Understanding Atoms
    • Our understanding of what’s inside atoms has developed in the last 200 years……..
  • 13. The Dalton Model In about 1810, James Dalton decided that matter was made of tiny, solid , spherical particles called atoms.
  • 14.
    • He introduced the idea of atoms as elementary particles.
  • 15. Electron microscope picture of Carbon Atoms
  • 16. Thomson’s Model of the Atom
    • In 1897, JJ Thomson discovered electrons, and suggested that the atom was a solid sphere of positive charge with electrons stuck in it like plums in a plum pudding.
  • 17. Copyright © Houghton Mifflin Company. All rights reserved. 2–19 Rutherford's Experiment On α-Particle Bombardment of Metal Foil Copyright © Houghton Mifflin Company. All rights reserved. 2–19 Rutherford's Experiment On α-Particle Bombardment of Metal Foil Thomson’s Model
  • 18. The Rutherford Model
  • 19. Rutherford’s Experiment
    • In 1909, Ernest Rutherford wanted to carry out an experiment to test Thomson’s Model.
    • We can’t see inside an atom with our eyes, but he wanted to “see” inside.
  • 20.
    • “ Seeing” inside things……
  • 21.
    • “ Seeing” inside things……
  • 22.  
  • 23.
    • “ Seeing” inside things……
  • 24.
    • He managed to “look inside” the atom by firing tiny particles called alpha particles at a thin gold foil to see how the alpha particles were deflected by the atoms of gold.
    • Alpha particles are the same as Helium nucleii, they are emitted from some radioactive atoms.
  • 25. detector Rutherford’s Gold Foil Experiment
  • 26. What they expected to happen: GOLD FOIL
  • 27. What did happen: GOLD FOIL
  • 28.
    • This is what they expected to happen
    • Thomson Model
    • They expected to see small or no deflection of the alpha particles
    • This is what did happen
    • Rutherford model
  • 29. Expected Results Actual Results
  • 30. Rutherford’s Experiment (1911)
    • Results:
    • Most particles go straight through.
    • Some particles are deflected from straight path. A few even go backwards
    • Interpretation:
    • Most of the atom is empty space.
    • nucleus must be positive , very dense , more massive than alpha particles.
    • Negative electrons orbit the nucleus, but are much lighter
  • 31. Rutherford’s Atom
  • 32. Scale of the atom.
    • If an atom was enlarged to the size of a stadium, the nucleus would be the size of a plum .
    • The electrons would be the size of match heads wizzing around the stands.
    The rest is empty space
  • 33. Size of the Atom
    • An atom is roughly 10 -10 m in diameter
    • This means a full stop is roughly ten million atoms across.
    • A small nucleus is roughly 10 -15 m in diameter
    • This is 1/100,000 ths the diameter of the atom
  • 34. Fundamental Forces
    • What are the only two Fundamental Forces you are familiar with?
    • Gravity
    • Electric
  • 35. How Do You Make An Atom?
    • Why don’t the electrons fall into the nucleus?
  • 36. Physicists realised the nucleus was made of two types of nucleons . Protons and Neutrons. What stops them flying apart? The strong nuclear force!!! extension… Now we’ll look closer at the nucleus
  • 37. Nuclear Notation
    • A nucleus can be described by two numbers:
    • Atomic or charge number (number of protons) ( Z )
    • Determines the nature of the atom and the element
    • Mass or nucleon number (Number of protons plus neutrons) ( A )
    • e.g.
  • 38. Isotopes : Atoms of an element with different number of neutrons e.g.
  • 39. Radioactive Decay
    • Nuclei that have too much energy are unstable.
    • They become more stable by firing out some nuclear radiation
    • There are three types of radioactive decay……
  • 40.  
  • 41. Write the equation for the alpha decay of Radium to Radon Alpha Decay
  • 42. Beta Decay
  • 43. Beta Decay
    • Write the equation for the beta decay of radium into actinium
    This is what causes beta decay beta decay is when a nucleus fires out an electron…
  • 44.  
  • 45. Gamma Decay
    • Write the equation for the gamma decay of……
    A gamma ray is a high energy photon emitted from a nucleus
  • 46. Ionisation
    • When alpha particles collide with atoms, they can knock electrons off.
    • This will produce a positive ion and a free electron.
  • 47. Positive ion
  • 48. Sorting by Absorption Paper 1mm Lead
  • 49. Sorting with a Magnetic Field
    • Identify each type of radiation
  • 50. Half Life
    • The half life of an isotope is the time taken for half of a sample to decay into another isotope.
    • OR, the time taken for the activity of a sample to halve.
    • The shorter the half life, the less stable it is.
    • e.g. Uranium 238: 4,500 MY
    • Radon 218 0.04 s
    • link to half life 1
  • 51. Radioactivity and Probability
    • Radioactivity is all about chance.
    • You can’t say when a certain nucleus will decay, but it might have a 1 in 10 chance of decaying in the next 5 seconds.
    • For the example above:
    • 1000 nuclei  100 decays in 5s
    • 100 nuclei  10 decays in 5s
  • 52.
    • This means there are more decays when there are more nuclei.
    • A shorter half life means a greater probability of a decay occurring
  • 53.
    • e.g Beryllium 11 decays to Boron 11 with a half life of 14 s
    • So If you have 16g of
    • Beryllium 11 now ,
    • after 14 s you will
    • have 8g etc.
    • link to half life 2
    8g 4g 2g 1g 56 42 28 14 16g 0 Amount of B Time(s)
  • 54. Berillium amount Time 16 g Now 8 g after one half life 4 g after two half lifes 1 HL 2 HL 3 HL 4 HL Boron amount
  • 55.
    • Note that the total mass of the sample is about the same , because as the Beryllium decays, it doesn’t disappear, it changes into Boron. The Boron is still there.
  • 56. Sample Question.
    • A radioactive isotope has a half life of 3 years.
    • A 5 g sample of the isotope produces 30 decays per sec.
    • What will the decay rate of a 1 g sample be in 9 years time?
  • 57. Carbon Dating
    • This image shows the Shroud of Turin.
    • It was supposedly the cloth that Christ was buried in. Is it real or a medieval fake???
  • 58.
    • In the Atmosphere, cosmic rays hit Nitrogen 14 changing it to Carbon 14.
    • The Carbon 14 decays with a half life of 6300 years.
    • So a small fraction of CO 2 molecules contain Carbon 14. This is taken in by plants, and hence animals.
    • When the organism dies, The Carbon 12 stays the same, the Carbon 14 decays.
    • By measuring the ratio of C14 to C12, the time since it was alive can be calculated
  • 59.
    • Back to the shroud. The ratio of C14 to C12 showed it was about 800 years old!!!
    • Final question. A wooden axe handle has a ratio of C14 to C12 that is 1/8 times the ratio for new wood.
    • How old is it?
  • 60. NCEA type question
    • Describe the Dalton model of the atom
    • Explain the evidence for the Thomson model
    • Explain the evidence for the Rutherford model
  • 61.
    • (a) Cobalt-60 undergoes radioactive decay..
    • Show how the decay of cobalt-60 ( ) results in nickel-60 ( ).
  • 62.
    • (a) A smoke detector contains radioactive americium  241 which emits radiation. Complete the following equation to identify the radiation emitted.
    • Explain why the radiation given out by the americium is unlikely to do any harm to the people living inside the house.
  • 63.
    • The alpha particles ionise atoms in the air. Explain what this means.
  • 64.
    • Estimate the half-life of americium-241.
  • 65.
    • (b) Radon-212 ( ) is a radioactive gas. Show that when radon-212 undergoes alpha decay, polonium is formed.
    • Radon-212 decays with a half-life of 24 minutes.
    • If you start with 96 mg of radon-212, find the approximate mass of polonium-208 two hours later.
    • Why is the actual mass less than your calculation?
  • 66. State what an alpha particle is. 12 years beta particle hydrogen-3 24 minutes beta particle uranium-239 less than 1 second alpha particle polonium-213 138 days alpha particle polonium-210 74 days gamma ray iridium-192 6 days gamma ray technetium-99 Half-life Type of radiation emitted Isotope
  • 67. Two isotopes of polonium are given in the table. How do the nuclei of these two isotopes differ? 12 years beta particle hydrogen-3 24 minutes beta particle uranium-239 less than 1 second alpha particle polonium-213 138 days alpha particle polonium-210 74 days gamma ray iridium-192 6 days gamma ray technetium-99 Half-life Type of radiation emitted Isotope
  • 68. A doctor needs to monitor the blood flow through a patient’s heart. She injects a radioactive isotope into the patient’s bloodstream. Explain why she would choose technetium-99 instead of the other isotopes listed in the table above. 12 years beta particle hydrogen-3 24 minutes beta particle uranium-239 less than 1 second alpha particle polonium-213 5 seconds gamma ray Strontium 91 74 days gamma ray iridium-192 6 days gamma ray technetium-99 Half-life Type of radiation emitted Isotope