PHYSICS - RADIOACTIVITY

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  • radioactivity
    • STRUCTURE OF AN ATOM
      • protons and neutrons have same relative mass of 1
      • nucleon (mass) number = number of protons and neutrons
      • proton (atomic) number = number of protons
      • proton charge = 1. neutron charge = 0. electron charge = -1
    • ATOMS AND IONS
      • number of protons determine the element
        • A (mass number / nucleon number / atomic number) = total number of nucleus
        • Z (proton number / atomic number) = total number of protons
        • number of neutrons = A-Z
      • ions - charge
        • if number of electrons changes, atom = charge, and now an ion
          • remove an electron, overall charge = positive so it is a POSITIVE ION
          • add an electron, overall charge = negative, so it is a NEGATIVE ION
    • GAMMA RAYS
      • electro-magnetic waves, so have no mass or charge
        • very short wave-length and highly energetic electro-magnetic radiation
      • high    penetrating power
        • takes thick sheet of metal or concrete to reduce them by a lot
      • weakly ionising
        • do not directly ionise other atoms
      • given off by energetic or excited nuclei
      • gamma radiation does not alter nucleon and proton numbers
      • not affected by electric or magnetic fields
    • EFFECT OF ALPHA AND BETA DECAY ON NUCLEI
      • radioactive decay occurs in unstable nuclei
      • parent nucleus ejects a particle to form a daughter
        • new nucleus is excited and loses energy by giving off a gamma ray
          • unstable   -> stable
    • ALPHA DECAY
      • very large nuclei that have a surplus of neutrons
      • most alpha emitters are heavy nuclei
      • mass number goes down by 4 -> 4 nucleons lost
      • atomic number goes down by 2 - 2 protons lost
      • helium nucleus is ejected
    • BETA DECAY
      • smaller nuclei with a surplus of neutrons
      • high speed electron is ejected
      • electron comes out of nucleus, not shells
    • HALF-LIFE
      • the time taken for the mass / number / percen-tage / activity of radio-active  nuclei to halve
  • if number of electrons changes, atom = charge, and now an ion
    • remove an electron, overall charge = positive so it is a POSITIVE ION
    • add an electron, overall charge = negative, so it is a NEGATIVE ION

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