Ionising Radiation from the NucleusOxford AQA IGCSE Physics: Revision notes

Radioactive decay is the random process by which an unstable nucleus emits particles or radiation in order to become more stable.

• The process is random: it is impossible to predict exactly when any individual unstable nucleus will decay
• When a nucleus decays, a different element may be formed (since the number of protons can change)
• Energy is emitted as a result of changes taking place within the nucleus

• Alpha particles (α): two protons and two neutrons — essentially a helium nucleus
• Beta particles (β): high-speed electrons emitted from the nucleus as a neutron turns into a proton
• Gamma rays (γ): electromagnetic radiation emitted from the nucleus

Background radiation is radiation that is present in the environment at all times, from sources including radioactive substances in the environment (rocks, soil), space (cosmic rays), and man-made devices such as X-ray machines.

There is a trade-off: the more strongly ionising a radiation type is, the less penetrating it tends to be, and vice versa.

Balanced nuclear equations can be written for alpha and beta decay by ensuring the mass numbers and atomic numbers balance on both sides of the equation.

Half-life is the average time taken for the number of nuclei of a radioactive isotope in a sample to halve, or equivalently, the time taken for the count rate (or activity) from a sample to fall to half of its initial level.

Half-life is used in calculations by repeatedly halving the count rate or number of nuclei for each half-life that passes.

Radioactive contamination is the unwanted presence of radioactive atoms on or in a material. The hazard comes from the decay of the contaminating atoms, which may continue for as long as they remain present.

Irradiation is exposing an object to ionising radiation from a source without it being in contact with radioactive material. An irradiated object does not itself become radioactive.

Precautions include: using tongs/shielding to handle sources, minimising exposure time, keeping distance from sources, and wearing protective clothing.

The hazard and appropriate use of a radioactive source depends on both the type of radiation it emits and its half-life — a source with a long half-life remains hazardous for longer, while a very short half-life may be more useful for certain medical procedures as the radioactivity decays away quickly.