radioactivity - 2

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  • radioactivity
    • ISOTOPES
      • atoms or nuclei that have the same number of protons, different number of neutrons
      • same chemical properties as the normal element
    • BACK GROUND RADIATION
      • all around us and little can be done to avoid it
      • most comes from natural sources
        • radon gas from the ground - makes up around half of background radiation
        • buildings and the ground
        • food and drink
        • cosmic rays
      • a small portion is from artificial sources
        • mostly medicine, then nuclear power and weapons, then other sources
    • GIEGER-MÜLLER TUBE
      • detects ionising radiations
      • tells us:  the number of particles detected per second
        • aka activity of the radioactive source with unit of Bequerels (Bq)
          • 1Bq = 1 decay per second
      • if pointed at a radioactive substance for a period of time, the counter attached to it the reading would decrease
      • radioactive substances can die away in micro-seconds to thousands of years
    • STABLE AND UNSTABLE NUCLEI
      • nucleus is unstable and will decay into a more stable atom
        • this radioactive decay is spontaneous and random
      • when an unstable nucleus decays, it may give out:
        • alpha particle
        • gamma ray
    • ALPHA PARTICLES
      • charge = +2
        • large charge means they are slow and heavy, and ionise other atoms strongly
      • atomic mass = 4
      • low penetrating power as they lose energy each time they ionise an atom
      • effect of electric or magnetic field =  deflection as a positive charge
    • BETA PARTICLES
      • effect of electric or magnetic field = deflection in opposite direction to alpha
      • charge = -1
      • fast and light, so ionise atoms as they pass but not as strongly as alpha
      • mass = 1/2000 of a proton
      • medium penetrating power
        • can be stopped by few cm of aluminum or plastics like perspex

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