AQA A Level Physics复习笔记8.1.6 Radiation Safety

• It is very well known that radioactive sources are dangerous if handled improperly
• When choosing a source to work with, the following characteristics are preferred:
  • Short-lived isotopes are preferred to long-lived ones
  • The smaller the amount of radioactive material, the better

   

• 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 does not penetrate as far

   

• The biggest risks when working with radioactive sources are exposure and contamination
  • Contamination happens when a piece of radioactive material is transferred onto a person, or a personal item, where it can then decay and cause damage

   

• The radiation hazard warning safety symbol is used to warn about hazardous materials, locations or objects

• 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 these 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

   

A badge containing photographic film can be used to monitor a person's exposure to radiation

• Radioactive materials can cause a huge amount of damage to the human body, however, under careful management, they can be of huge benefit 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