Radioactive Decay

Key Stage 4

Meaning

Radioactive decay is when an unstable isotope emits a particle or electromagnetic wave to become more stable.

About Radioactive Decay

During a radioactive decay an unstable isotope may emit:

• Alpha Radiation - An ionising radiation which is two protons and two neutrons (a Helium nucleus).
• Beta Radiation - An ionising radiation which is a fast moving electron ejected from the nucleus.
• Gamma Radiation - An ionising radiation which is a very high frequency electromagnetic wave emitted from the nucleus.
• Neutron Radiation - A form of indirectly ionising radiation consisting of a single neutron ejected from the nucleus. It causes ionisation by causing other elements to become unstable releasing gamma radiation.

The rate of radioactive decay is known as the 'Half Life' which is how long it takes for half of the unstable isotopes in a sample of radioactive material to decay. This time is a constant for each type of radioactive material regardless of the quantity of unstable isotopes.

Examples

This is a key to show the types of particles in the following decays of unstable nuclei.

This nucleus is unstable because it is too massive and has too few neutrons relative to protons so it decays via alpha emission reducing the atomic mass by 4 and the atomic number by 2. \({}_Z^AX \rightarrow {}_{Z-2}^{A-4}Y + {}_2^4\alpha\)	This nucleus is unstable because it is too many neutrons so it decays via beta emission in which a neutron turns into a proton increasing the atomic number by 1. \({}_Z^AX \rightarrow {}_{Z+1}^{A}Y + {}_{-1}^0\beta\)

This nucleus is unstable because it is has excess vibrational energy so it decays by emitting a gamma ray. After the decay it still has the same atomic mass and atomic number but is no longer vibrating. \({}_Z^AX \rightarrow {}_Z^AX + {}_0^0\gamma\)	This nucleus is unstable because it has too many neutrons relative to protons so it decays via neutron radiation reducing the atomic mass by 1. \({}_Z^AX \rightarrow {}_{Z}^{A-1}Y + {}_0^1n\)

References

AQA

Radioactive decay, pages 198-201, GCSE Combined Science; The Revision Guide, CGP, AQA

Radioactive decay, pages 343-4, 347-9, GCSE Combined Science Trilogy 1, Hodder, AQA

Radioactive decay, pages 96-97, 100-101, GCSE Physics; Third Edition, Oxford University Press, AQA

Radioactive decay, pages 98-101, GCSE Physics, Hodder, AQA

Radioactive decay; alpha, pages 198, 199, 201, GCSE Combined Science; The Revision Guide, CGP, AQA

Radioactive decay; beta, pages 198, 199, 201, GCSE Combined Science; The Revision Guide, CGP, AQA

Radioactive decay; gamma, pages 198, 199, 201, 223, GCSE Combined Science; The Revision Guide, CGP, AQA

Radioactive; contamination, page 120, GCSE Physics; Student Book, Collins, AQA

Radioactive; decay, pages 109, 112-13, 116-19, 217, GCSE Physics; Student Book, Collins, AQA