Radioactivity Medical PhysicsUnit 20 strand 1 (part)
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
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
Atomic structure Atoms consist of a nucleus and electrons The nucleus is made up of protons and neutronsBlockbusters game
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.
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
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.
Characteristics of alpha, beta (β+ and β–) and gammaradiations
• 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.
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)