Radiation Safety (AQA A Level Physics): Revision Note

Safe Handling of Radioactive Sources

• The risk associated with radioactive materials depends on the amount and type of radiation

  • For example, alpha radiation is more ionising than gamma radiation but less penetrating

• The damage done by exposure to radiation can be described by the received radiation dose or dose equivalent

• Dose equivalent, measured in Sieverts (Sv), depends on

  • The amount of energy absorbed per kilogram of a body

  • The type of radiation absorbed

• To minimise the received radiation dose of a sample:

  • Short-lived isotopes are preferred to long-lived ones

  • The smaller the sample of radioactive material, the better

The radiation hazard warning safety symbol is used to warn about hazardous materials, locations or objects in the near vicinity

• Precautions must be taken to reduce the risk of harm when using radioactive sources. These include:

  • Keeping radioactive sources shielded when not in use, for example in a lead-lined box

  • Wearing protective clothing to prevent the body from becoming contaminated

  • Keeping personal items outside of the room to prevent them from becoming contaminated

  • Limiting exposure time so less time is spent with radioactive materials

  • Handling radioactive materials with long tongs to increase the distance from them

  • Monitoring the exposure of workers, such as radiographers, using detector badges

Radiation in Medicine

Radiation Therapy

• Gamma radiation can be used to destroy cancerous tumours

  • The gamma rays are concentrated on the tumour to protect the surrounding tissue

• Less penetrating beta radiation can be used to treat skin cancer by direct application to the affected area

A radiotherapy machine. Powerful radiation is directed at the tumour and lead sheets can be used to prevent healthy tissue from being damaged

• Precautions for the patient:

  • The patient should be protected with lead to cover parts of the body not to be exposed to radiation

  • The exact dose should be calculated carefully

  • The dose should be directed very accurately at the cancerous tissue to minimise damage to healthy tissue

• Precautions for the radiographer:

  • The radiographer should handle the source remotely with tongs or a machine

  • The radiographer should be protected by a screen

  • The radiographer should be a long way from the source while the dose is given

  • The source should be immediately stored in its lead case once the dose is given

Radioactive Tracers

• Radioisotopes can be used as ‘tracers’ to monitor the processes occurring in different parts of the body

• Radioactive tracers with a short half-life are preferred because:

  • Initially, the activity is very high, so only a small sample needed

  • The shorter the half-life, the faster the isotope decays

  • Isotopes with a shorter half-life pose a much lower risk to the patient

  • The medical test doesn‘t last long so a half-life of a few hours is enough

A radioactive tracer must be injected into the patient in order to take PET scan images of brain activity

• One example is Iodine-131

  • This isotope is known to be specifically taken up by the thyroid gland making it useful for monitoring and treating thyroid conditions

  • It emits beta particles which means it will stay concentrated on the thyroid area and nowhere else in the body

  • It has a short half-life of 8 days meaning it will not be around too long to cause prolonged exposure

• Another isotope commonly used as a tracer is Technetium-99m

  • It is a gamma emitter with an energy of about 140 keV which is ideal for detection

  • It has a half-life of 6 hours so it is ideal for use as a tracer, but will not remain active for too long and can be tolerated by the body

  • Gamma radiation is ideal as it is the most penetrating so it can be detected outside the body

  • Also, gamma is the weakest ioniser and causes minimal damage

  • As well as this, technetium-99m may be prepared easily at the hospital when required making it a cost-effective treatment

Sterilising Medical Equipment

• Gamma radiation is widely used to sterilise medical equipment

• Gamma is most suited to this because:

  • It is the most penetrating out of all the types of radiation

  • It is penetrating enough to irradiate all sides of the instruments

  • Instruments can be sterilised without removing the packaging

• The general public might be worried that using gamma radiation in this way might cause the equipment itself to become radioactive, however, this is not the case because:

  • In order for a substance to become radioactive, the nuclei have to be affected

  • Ionising radiation only affects the outer electrons and not the nucleus

  • The radioactive material is kept securely sealed away from the packaged equipment so there is no chance of contamination