OCR A Level Physics

Revision Notes

6.9.2 Alpha, Beta & Gamma Radiation

Test Yourself

Alpha, Beta & Gamma Particles

  • Some elements have nuclei that are unstable
    • This tends to be when the number of nucleons does not balance

  • In order to become more stable, they emit particles and/or electromagnetic radiation
    • These nuclei are said to be radioactive

  • There are three different types of radioactive emission: Alpha, Beta and Gamma

Alpha Particles

  • Alpha (α) particles are high energy particles made up of 2 protons and 2 neutrons (the same as a helium nucleus)
  • They are usually emitted from nuclei that are too large

Alpha particle, downloadable AS & A Level Physics revision notes

 

  • Alpha is a low penetrating type of radiation
    • Alpha particles have a range of a few cm in air

Beta Particles

  • Beta (β) particles are high energy electrons emitted from the nucleus
    • β particles are emitted by nuclei that have too many neutrons

  • Beta is a moderately ionising type of radiation
    • This is due to it having a charge of +1e
    • This means it is able to do some slight damage to cells (less than alpha but more than gamma)

  • Beta is a moderately penetrating type of radiation
    • Beta particles have a range of around 20 cm - 3 m in air, depending on their energy

  • Beta can be stopped by a few millimetres of aluminium foil

6-9-2-beta-particle_ocr-al-physics

Gamma Rays

  • Gamma (γ) rays are high energy electromagnetic waves
  • They are emitted by nuclei that need to lose some energy

Gamma particle, downloadable AS & A Level Physics revision notes 

  • Gamma is a highly penetrating type of radiation
    • Gamma particles have a range of around 1- 10 cm in lead or several metres in concrete

  • If these particles hit other atoms, they can knock out electrons, ionising the atom
  • This can cause chemical changes in materials and can damage or kill living cells

Ionisation, downloadable AS & A Level Physics revision notes

When radiation passes close to atoms, it can knock out electrons, ionising the atom

  • The properties of the different types of radiation are summarised in the table below

Table properties of alpha, beta, gamma radiation, downloadable AS & A Level Physics revision notes

  • u is the atomic mass unit (see “Atomic Mass Unit (u)”)
  • e is the charge of the electron: 1.60 × 10-19 C
  • c is the speed of light: 3 × 108 m s-1

Worked example

ANSWER:     D

Worked example - alpha beta gamma particles (2), downloadable AS & A Level Physics revision notes

Exam Tip

It is important to be confident with the properties of each type of radiation and how they can be written as symbols.

Investigating the Absorption of Alpha, Beta & Gamma Radiation

Aim of the Experiment

  •  The aim of this experiment is to investigate the penetration powers of different types of radiation using either radioactive sources or simulations

Variables:

  • Independent variable = Absorber material
  • Dependent variable = Count rate
  • Control variables:
    • Radioactive source
    • Distance of GM tube to source
    • Location / background radiation

Investigating Radiation Equipment list, downloadable IGCSE & GCSE Physics revision notes

Method

Investigating Radiation Apparatus, downloadable IGCSE & GCSE Physics revision notes

Investigating radiation apparatus

  1. Connect the Geiger-Müller tube to the counter and, without any sources present, measure background radiation over a one minute period
  2. Repeat this three times, and take an average
  3. Now place a radioactive source a fixed distance of 3 cm away from the tube and take another reading over a one minute interval
  4. Now take a set of absorbers: some paper, several different thicknesses of aluminium (increasing in 0.5mm intervals) and different thickness of lead
  5. One at a time, place these absorbers between the source and the tube and take another reading over a one minute interval
  6. Repeat the above experiment for other radioactive sources

Results

  • Alpha radiation will be absorbed by the paper
  • Beta radiation will be absorbed by the aluminium foil
  • Some gamma radiation will be absorbed by the thick lead

Radiation Stopping Distances, downloadable AS & A Level Physics revision notes

 Penetrating power of alpha, beta and gamma radiation

Safety Considerations

  • When not using a source, keep it in a lead lined container
  • When in use, try and keep a good distance (a metre or so) between yourself and the source
  • When handling the source, do so using tweezers (or tongs) and point the source away from you

Exam Tip

It is common for you to be asked questions on this practical. Make sure you are familiar with the safety procedures and why you would measure the background radiation first before completing the experiment. 

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