CIE AS Physics (9702) 2019-2021

Revision Notes

13.1.3 Alpha, Beta & Gamma Particles

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 (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

 

  • Beta (β) particles are high energy electrons emitted from the nucleus
  • Beta (β+) particles are high energy positrons (antimatter of electrons) also emitted from the nucleus
    • β particles are emitted by nuclei that have too many neutrons
    • β+ particles are emitted by nuclei that have too many protons

Beta particle, downloadable AS & A Level Physics revision notes

 

  • 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

 

  • 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

Worked example - alpha beta gamma particles (1), downloadable AS & A Level Physics revision notes

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

Neutrino Emission

  • An electron neutrino is a type of subatomic particle with no charge and negligible mass which is also emitted from the nucleus
  • The anti-neutrino is the antiparticle of a neutrino
    • Electron anti-neutrinos are produced during β– decay
    • Electron neutrinos are produced during β+ decay

Neutrino Emission, downloadable AS & A Level Physics revision notes

Exam Tip

One way to remember which particle decays into which depends on the type of beta emission, think of beta ‘plus’ as the ‘proton’ that turns into the neutron (plus an electron neutrino)

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