CIE A Level Physics复习笔记11.1.3 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

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

Gamma Rays

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

• 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

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

• 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

ANSWER:     D