Count Rate
Contents
Key Stage 4
Meaning
Count rate is the number of particles of ionising radiation that reach a detector per second.
About Count Rate
- The SI Units of count rate are Becquerels (Bq).
- Count rate is measured using a Geiger counter.
- The count rate at the detector will be less than the radioactivity of the sample of unstable isotope because the ionising radiation spreads out in all directions equally.
- The greater the distance from the radioactive sample the lower the count rate.
- For an alpha source the count rate drops to 0 beyond 5cm because the alpha particles are absorbed by a few centimetres of air.
- For a beta source the count rate drops to 0 beyond a few metres because the beta particles are absorbed by the several metres of air.
- For a gamma-ray source the count rate drops at a rate of 1/r2 where r is the distance between the source and detector.
References
AQA
- Count rate, page 118, GCSE Combined Science Trilogy; Physics, CGP, AQA
- Count rate, page 130, GCSE Physics; The Complete 9-1 Course for AQA, CGP, AQA
- Count rate, radioactive sources, page 348, GCSE Combined Science Trilogy 1, Hodder, AQA
- Count rates, page 100, GCSE Physics; Third Edition, Oxford University Press, AQA
Edexcel
- Count rate, page 361, GCSE Combined Science, Pearson Edexcel
- Count rate, page 97, GCSE Physics, Pearson Edexcel