7.4 - Radiation & Radioisotopes
Radioactive decay and radioisotopes
- Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons (the same atomic number, but different mass numbers).
- A radioisotope is an isotope with an unstable nucleus.
- An unstable nucleus breaks down, giving out radiation as it changes into a more stable arrangement. This process is radioactive decay, and a substance containing radioisotopes is radioactive.
Where the change happens
- The change happens in the nucleus of the atom, not in the electrons around it, which is what makes radioactive decay different from a chemical reaction.
- Because the make-up of the nucleus changes, the atom usually ends up as an atom of a different element.
- The radiation emitted comes in three kinds: alpha, beta, and gamma.
Alpha, beta and gamma radiation
- Alpha radiation (α) - Given out as alpha particles, each made of two protons and two neutrons (identical to a helium nucleus). It carries a 2+ charge.
- Beta radiation (β) - Given out as beta particles, which are fast-moving electrons ejected from the nucleus. It has virtually no mass and a 1- charge.
- Gamma radiation (γ) - Given out as gamma rays, which are high-energy electromagnetic waves emitted from the nucleus. It carries energy rather than particles, so it has no mass and no charge.
Comparing the three types
| Property | Alpha (α) | Beta (β) | Gamma (γ) |
|---|---|---|---|
| Range in air | A few centimetres | Over a metre | Great distances |
| Stopped by | A sheet of paper | A thin sheet of aluminium, around 5 mm | Thick lead or metres of concrete |
| In an electric field | Attracted towards a negatively charged plate | Attracted towards a positively charged plate | Not deflected |
TermDefinition
IsotopeOne of two or more forms of the same element whose atoms have the same number of protons but different numbers of neutrons.
RadioisotopeAn isotope with an unstable nucleus that gives out radiation as it decays.
Radioactive decayThe random process where an unstable nucleus breaks down and releases radiation to become more stable.
Alpha particleA particle made of two protons and two neutrons that is emitted from a nucleus during alpha decay.
Beta particleA fast-moving electron emitted from a nucleus when a neutron changes into a proton.
Gamma rayVery high-frequency electromagnetic radiation, usually given out by an unstable nucleus as it loses energy. Giving it out does not change the number of protons or neutrons.