Types of Radiation (AQA GCSE Physics)

• When an unstable nucleus decays it emits radiation, called nuclear radiation
• There are different types of radiation that can be emitted:
  • Alpha
  • Beta
  • Gamma
  • Neutrons

Alpha Particles

• The symbol for alpha is α
• An alpha particle is the same as a helium nucleus
  • This is because they consist of two neutrons and two protons

• Alpha particles have a charge of +2
  • This means they can be affected by an electric field

Beta Particles

• The symbol for beta is β
• Beta particles are fast-moving electrons
• They are produced in nuclei when a neutron changes into a proton and an electron
• Beta particles have a charge of -1
  • This means they can be affected by an electric field

Gamma Rays

• The symbol for gamma is γ
• Gamma rays are electromagnetic waves
• They have the highest energy of the different types of electromagnetic waves
• Gamma rays have no charge

Neutrons

• The symbol for a neutron is n
• Neutrons are one of the two particles found in the nucleus of atoms
• Neutrons are neutral, they have no charge

Alpha particles, beta particles, gamma waves and neutrons can be emitted from unstable nuclei

Properties of Alpha, Beta and Gamma Radiation

• The properties of Alpha, Beta and Gamma are given in this table, and then described in more detail below

Different Properties of Nuclear Radiation

• The trend down the table shows:
  • The range increases
  • Penetrating power increases
  • Ionisation decreases

Penetrating Power

• Alpha, beta and gamma have different properties
• They penetrate materials in different ways
  • This means they are stopped by different materials

Alpha, beta and gamma are different in how they penetrate materials. Alpha is the least penetrating, and gamma is the most penetrating

• Alpha is stopped by paper, whereas beta and gamma pass through it
• Beta is stopped by a few millimetres of aluminium
  • Gamma can pass through aluminium

• Gamma rays are only partially stopped by thick lead

Ionising Power

• All nuclear radiation is capable of ionising atoms that it hits
• When an atom is ionised, the number of electrons it has changes
• This gives it a non-zero charge

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

• Alpha radiation is the most ionising form of nuclear radiation
  • This is because alpha particles have a charge of +2

• Gamma radiation is the least ionising form of nuclear radiation

Range in Air

• The more ionising a form of radiation is, the sooner it will react with the air it is moving through
• Strongly ionising radiation has the shortest range in air
  • Alpha only travels a few centimetres in air
  • Beta has a range of a few tens of centimetres
  • Gamma is not absorbed by air and so has an infinite range, although it does get less intense with distance

ANSWER:  B

• • The answer is not A because the radiation passed through the paper almost unchanged
    • This means it is not alpha

  • The answer is not C or D because the aluminium decreased the count-rate significantly
    • This means it is not gamma (gamma penetrates aluminium)
    • This also means it is not neutrons (neutrons penetrate aluminium, however you do not need to know this for your GCSE)

  • Therefore, the source must be Beta particles