Radioactive decay and nuclear radiation · GCSE Physics

Radioactive decay

Some atomic nuclei are unstable. The nucleus gives out radiation as it changes to become more stable. This is radioactive decay, and it is a random process.
Activity is the rate at which a source of unstable nuclei decays, measured in becquerels (Bq). 1 Bq = 1 decay per second.
Count rate is the number of decays recorded each second by a detector, such as a Geiger–Müller tube.

Alpha particle (α): two protons and two neutrons, the same as a helium nucleus.
Beta particle (β): a high-speed electron ejected from the nucleus as a neutron turns into a proton.
Gamma ray (γ): electromagnetic radiation from the nucleus.
A nucleus can also emit a neutron.

Alpha: strongly ionising; travels only a few centimetres in air; stopped by a sheet of paper or skin.
Beta: moderately ionising; travels about a metre in air; stopped by a few millimetres of aluminium.
Gamma: weakly ionising; travels a very long distance in air; reduced by several centimetres of lead or a thick layer of concrete.

Alpha decay: the mass number goes down by 4 and the atomic number by 2. Example: ²¹⁹₈₆Rn → ²¹⁵₈₄Po + ⁴₂He.
Beta decay: the mass number stays the same and the atomic number goes up by 1. Example: ¹⁴₆C → ¹⁴₇N + ⁰₋₁e.
Gamma emission does not change the mass or the charge of the nucleus.
In every equation, the mass numbers and the atomic numbers must balance on both sides.

Radioactive decay: The random process in which an unstable nucleus gives out radiation to become more stable.
Activity: The rate at which a source decays, measured in becquerels (Bq).
Count rate: The number of decays recorded each second by a detector.
Alpha particle: Two protons and two neutrons (a helium nucleus).
Beta particle: A high-speed electron from the nucleus, formed when a neutron turns into a proton.
Gamma ray: High-energy electromagnetic radiation emitted from the nucleus.
Ionising: Able to knock electrons off atoms, forming ions.
Geiger–Müller tube: A detector that measures nuclear radiation.