20 1 radioactivity


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20 1 radioactivity

  1. 1. Radioactivity Medical PhysicsUnit 20 strand 1 (part)
  2. 2. To achieve a pass grade the To achieve a merit grade theevidence must show that the evidence must show that, inlearner is able to: addition to the pass criteria, the learner is able to:P1 describe radioactivity, M1 explain the randomincluding atomic structure nature of decay and how it relates to half-life
  3. 3. What is radiation?The nuclei of some atoms are unstable. In order to achieve stability theyemit radiation.These materials are called radionuclides.They are radioactive.Radioactivity is a nuclear process – it is not a chemical process. It is notpossible to control the rate of radioactive breakdown of a nuclei, it is arandom process Radioactivity: industrial applications
  4. 4. Background radiation
  5. 5. Atomic structure Atoms consist of a nucleus and electrons The nucleus is made up of protons and neutronsBlockbusters game
  6. 6. Characteristics of alpha, beta (β+ and β–) and gammaradiationsThere are three types of radiation that can be emitted from a nucleus of anunstable atom.Alpha (α)and beta (β) are particles of matterGamma (γ) rays are photon of electromagnetic radiation, with a higherfrequency than an x-ray.
  7. 7. Characteristics of alpha, beta (β+ and β–) and gamma radiations Particle Constituent Charge Mass Alpha (α) Helium nucleus +2 4 2 protons and 2 neutronsBeta- minus (β-) Electron -1 Negligible Beta-plus (β+) Positron +1 Negligible Gamma (γ) Short-wave, high 0 0 frequency em wave
  8. 8. Particle Ionising Range Speed Affected by magnetic field? Alpha (α) Strong –easily pull Slow Yes electrons off atoms (10 000 ionisations per particle)Beta- minus (β-) Weakly (100 atoms Fast Yes per particle) Beta-plus (β+) Annihilated by electron – so zero range Gamma (γ) Very weakly Speed of light No Gamma radiation spreads out very quickly. Its intensity decreases by the inverse square law.
  9. 9. Characteristics of alpha, beta (β+ and β–) and gammaradiations
  10. 10. •random nature of radioactive decay
  11. 11. • The half-life of a radioactive isotope is defined as thetime it takes for the number of nuclei of the isotope in asample to halve or the time it takes for the count ratefrom a sample containing the isotope to fall to half itsinitial level.
  12. 12. Half-life
  13. 13. ResourcesSpecific textsJean Pope Medical Physics: Imaging (Heineman Advanced Science )Roger Muncaster Medical Physics (A-Level Physics) Cheltenham: Stanley Thornes(Publishers) LtdMartin Hollins (1990) Medical Physics (University of Btah Macmillan Science 16-19Project) Basingstoke: MacmillanJohn Ball and Adrian Moore (1997 3rd edn) Essential Physics for RadiographersOxford: BlackwellGeneral Physics booksKeith Johnson, Simmone Hewett, Sue Holt, John Miller (2000) Advanced Physics forYou Cheltenham: Nelson Thornes.Ch 27 on RadioactivityKen Dobson, David Grace and David Lovett (2002 2nd edn) Physics (CollinsAdvanced Science)Ch 19 Medical PhysicsClaire Thomas and Julie Wakeling (ed.) AS-Level Physics The Revision Guide (CGP)