Applications eg to safe handling of radioactive sources.

The idea

This note covers radiation safety when handling radioactive sources. Alpha particles are strongly ionising but travel only a few centimetres in air and are stopped by paper, so an alpha source is safe if kept outside the body. Beta particles need a few millimetres of a low-Z absorber like aluminium to minimise bremsstrahlung X-ray production, which high-Z materials like lead increase. Gamma rays need thick lead or concrete as they are highly penetrating. Safe handling uses time, distance and shielding: minimise exposure time, handle sources with tongs at arm's length, store them in lead-lined containers, and monitor dose with a film badge. These principles apply to all sources to prevent hazardous internal and external exposure.

What earns the marks

• Alpha particles are highly ionising but have a short range in air, so external exposure is low risk while internal exposure is serious.
• Beta particles require a few millimetres of a low-Z absorber such as aluminium or Perspex, as high-Z absorbers like lead produce more bremsstrahlung.
• Gamma rays are penetrating and need dense, thick shielding such as lead or concrete to attenuate them.
• Safe handling reduces dose by minimising time, maximising distance and using appropriate shielding.
• Sealed sources should be handled with tongs, stored in labelled containers and never pointed towards people.
• Dose monitoring with a film badge or Geiger–Müller tube provides evidence that exposure is being controlled.

Common mistakes and how to put them right

• Thinking that any absorber stops all radiation.

  Put it right: Is that alpha is stopped by paper, beta by a few millimetres of aluminium, and gamma is only attenuated by thick lead or concrete.

• Believing distance does not matter because shielding is present.

  Put it right: Is that intensity falls with distance, so tongs and remote handling reduce dose further.

• Treating an alpha source as harmless because its range is short.

  Put it right: Is that inhaled or swallowed alpha emitters deliver concentrated dose to living tissue and must be kept sealed.

Exam tips

• Name the radiation type and match it to a specific absorber with a reason, rather than writing 'lead stops radiation' for every case.
• Use the time–distance–shielding framework to structure safety answers and apply each factor to the source in the question.
• Remember that low-Z materials are preferred for shielding beta sources to minimise the production of penetrating bremsstrahlung X-rays.