Unit 5 Atomic physics


Section 5.2 Radioactivity

Detection of radioactivity

  • Many nuclei of elements in the periodic table are stable but some are unstable. Unstable nuclei undergo radioactive decay.
  • When a radioactive nucleus decays it may emit one or more of the following: alpha particles, beta particles or gamma rays.
  • The radiations alpha, beta and gamma have their own individual characteristics, as shown in the table below. Alpha particle
    Nature 2 protons and 2 neutrons (helium nucleus)
    Symbol α or 24 He
    Charge positive
    Affected by magnetic and electric fields yes
    Penetrating power weak – stopped by thin paper
    Relative ionising effect strongest
    Dangerous yes
    Beta particle
    Nature electron
    Symbol β or –10 e
    Charge negative
    Affected by magnetic and electric fields yes
    Penetrating power moderate – stopped by a few mm of aluminium
    Relative ionising effect medium
    Dangerous yes
    Gamma ray
    Nature electromagnetic radiation
    Symbol γ
    Charge uncharged
    Affected by magnetic and electric fields no
    Penetrating power strong – only stopped by many cm of lead or many m of concrete
    Relative ionising effect weakest
    Dangerous yes
  • There is always radiation present all around us. This is known as background radiation. Background radiation comes from cosmic rays, rocks and atmospheric gases. A small amount (about 3%) of background radiation comes from human-made sources such as medical equipment, nuclear power stations and nuclear weapons testing.
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