.1 Radioactive decay and nuclear radiation

• Some atomic nuclei are unstable. The nucleus gives out radiation as it changes to become more stable. This is a random process called radioactive decay.
• Activity is the rate at which a source of unstable nuclei decays.
• Activity is measured in becquerel (Bq)
• Count-rate is the number of decays recorded each second by a detector (eg Geiger-Muller tube)
• The nuclear radiation emitted may be:

  an alpha particle (α) – this consists of two neutrons and two protons, it is the same as a helium nucleus

  a beta particle (β) – a high speed electron ejected from the nucleus as a neutron turns into a proton

  a gamma ray (γ) – electromagnetic radiation from the nucleus

  a neutron (n).