Nuclear Decay and Half-life

• Some atomic nuclei are unstable and gives out radiation to become more stable
• Radioactive decay is a random process
• 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 (e.g. Geiger-Muller tube)
• An alpha particle (α) consists of two neutrons and two protons
• An alpha particle (α) is the same as a helium nucleus
• A beta particle (β) is a high speed electron ejected from the nucleus as a neutron turns into a proton
• A gamma ray (γ) is electromagnetic radiation from the nucleus
• Alpha radiation is strongly ionising
• Beta radiation is moderately ionising
• Gamma rays are weakly ionising
• Gamma rays can be absorbed by thick sheets of lead
• Gamma rays can be absorbed by metres of concrete
• Beta particles can be absorbed by sheets of aluminium
• Alpha particles can absorbed by paper
• Alpha radiation can travel a few cm in air
• Beta radiation can travel a few metres in air
• Gamma rays can travel a few 1000 metres in air
• Nuclear radiation emitted may be a neutron
• Radioactive decay is random
• The half-life is the time taken for the number of unstable nuclei of an isotope to halve
• The half-life is the time taken for the count rate (or activity) from a sample containing an isotope to fall to half its initial level