Annual Effective Dose Limits (SQA National 5 Physics): Revision Note

Annual effective dose limits

• The annual effective dose limit is defined as:

The maximum equivalent dose (H) that should be received per year

• The equivalent dose is a measure of how harmful a dose of radiation is

  • The unit is sieverts (Sv)

  • However, 1 Sv is a very large amount, so millisieverts (mSv) are often used

• The annual effective dose limit for a member of the public is 1 mSv

• The annual effective dose limit for a radiation worker is 20 mSv

• These limits exclude the average amount of background radiation that everyone is consistently exposed to

• The average annual background radiation in the UK is 2.2 mSv

  • Therefore, the general public is recommended to be exposed to no more than 1 mSv above the average background radiation per year

• The annual effective dose limits are used to assess workplace safety in different situations where workers are exposed to radiation

• For example:

  • Dentists who commonly perform X-rays

  • Radiologists

  • Nuclear power technicians

  • Aircraft crew

• It is also used for risk assessment to keep members of the public safe

• For example:

  • Travelling on an aeroplane

  • Radon levels in residential areas

  • Setting industry safety standards for radiation use

  • Setting safety standards for locations where radiation is, or has been used

• Medical procedures are not included in the annual effective dose limit for members of the public

  • The risks of radiation exposure have to be weighed against the benefits of medical treatment for each patient individually