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Alpha, Beta & Gamma Radiation

Physics: IB Diploma Higher Level, topic 5.1.5

Alpha (α) Radiation

Unstable nuclei emit one of three types of radiation: alpha, beta and gamma.

Properties of α radiation

Properties of α radiation

  • Alpha particles are:
  • Two protons and two neutrons bound together (the equivalent of a helium nucleus).
  • Weakly penetrating.
  • Easily absorbed.
  • Positively charged.
Properties of α radiation 2

Properties of α radiation 2

  • Alpha particles can only be emitted by nuclei with an atomic number greater than 82.
  • Typically, alpha particles cannot penetrate through a sheet of paper or a few mm of air.
Applications of α radiation

Applications of α radiation

  • An alpha source is used in fire alarms.
  • Alpha particles cannot penetrate through smoke. This is detected and sets off the alarm.

Beta Radiation

Unstable nuclei emit one of three types of radiation: alpha, beta and gamma.

Properties of β radiation

Properties of β radiation

  • Beta particles are:
  • Electrons (or positrons) that are emitted from an unstable nucleus.
  • Moderately penetrative.
  • Either positively or negatively charged.
  • Beta plus particles emitted by proton-rich nuclei.
  • Beta minus particles emitted by neutron rich nuclei.
Applications of beta particles

Applications of beta particles

  • Typically, beta particles cannot penetrate through about 5 mm of aluminum or about 30 cm of air.
  • A beta source is used for gauging the thickness of aluminum sheeting or foil.
  • A beta-plus emitter is used in medical PET scanning.

Gamma Radiation

Unstable nuclei emit one of three types of radiation. alpha, beta and gamma.

Properties of γ radiation

Properties of γ radiation

  • Gamma radiation:
  • Does not change the proton or nucleon number of a nucleus.
  • Makes the nucleus more stable by its emission.
  • Is highly penetrative.
  • Can be absorbed by several centimetres of lead, many metres of air and can travel through a vacuum indefinitely.
Properties of γ radiation 2

Properties of γ radiation 2

  • Gamma radiation is part of the electromagnetic spectrum.
  • Gamma radiation follows an inverse square law:
  • intensity at distance x from the source =constantx2= \frac{constant}{x^2}
Applications

Applications

  • Gamma radiation is used extensively in medical imaging, curing cancer by destroying tumorous cells and for sterilizing medical equipment.
  • It can be used to irradiate food to stop food from going bad.

Test yourself on Alpha, Beta & Gamma Radiation

  • What are alpha particles made of?

  • How far can gamma-rays travel through a vacuum?

  • Types of Radiation

  • Types of Radiation

  • Which of these are uses of gamma radiation?

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