3.5 - Dosimetry and Safety Flashcards
What is ‘Half Life’?
The time taken for the activity of a particular source to halve
What is the ‘activity’ of a radioactive source?
The number of decays per second (Bq)
What is ‘Absorbed dose’?
The energy absorbed per unit mass of the absorbing material (Gy/Jkg-1)
What is the ‘radiation weighting factor’?
The value given to each kind of radiation as a measure of its biological effect
What is the ‘Equivalent dose’?
The product of absorbed dose and radiation weighting factor (Sv)
What is the ‘Equivalent Dose Rate’?
This is the equivalent dose per unit time (Svx-1, where x is unit time)
What 3 factors does the risk of biological harm from an exposure to radiation depend on?
- The absorbed dose
- The kind of radiation
- The body organs or tissues exposed
What are 2 main natural sources of background radiation?
- Rocks of earth
* Cosmic rays from space
What are 2 main artificial sources of background radiation?
- Medical uses
* Weapons testing
What is the average annual effective dose that a person in the UK receives due to natural sources?
2mSv
Who have annual effective dose limits been set for? And who have higher limits been set for?
- The general public
* Workers in certain occupations
Describe the principles of a method for measuring the half value thickness of an absorber (6)
- Without the source, measure the background count rate
- Set the source a fixed distance in front of the detector and measure the count rate again
- Place plates of the material being investigated between the source and the detector to make different measured thicknesses, and each time measure the count rate again
- Subtract the background count rate from the readings to obtain the corrected count rates
- Draw a graph of the corrected count rate against thickness
- Note the thickness that causes the count rate to half
How can you reduce the equivalent dose rate? (2)
- Shielding
* Increasing the distance from the source
