Dose Rate
Published: Oct 12, 2018
Dose rate is a term applied for the rate at which Ionising Radiation is being absorbed by a medium (e.g. tissue). Whilst it is accurate to apply a prefix or postfix (e.g. 'absorbed dose rate'), the term is probably most often applied to Effective dose, which is a useful quality in expressing harm or overall risk of harm from whole body irradiation.
In the UK Ionising Radiations Regulations 2017 (IRR17), dose rate has a specific meaning which is stated as 'in relation to a place, the rate at which a person or part of a person would receive a dose of ionising radiation from external radiation if that person were at that place, being a dose rate at that place averaged over one minute'. For the UK this is an important definition, particularly where there might be very short term higher instantaneous dose rates (IDR) for a few seconds, where otherwise the dose rate is no greater than background. Workplaces such as linear accelerator medical treatment rooms could fall into this category, where the higher dose rate beam rotates around a primary shield - yielding a higher IDR (say 10 micro Sv/h) for 2 seconds, but otherwise yielding background (say 0.05 micro Sv/h) for the rest of the minute. In this example the dose rate, averaged over a minute, would be < 0.4 micro Sv/h. The same analysis can be applied to cargo / freight / food / beverage x-ray screening systems which use a shielded curtain which will open and close as items pass through.