Dose rate

A dose rate is quantity of radiation absorbed or delivered per unit time. It is often indicated in micrograys per hour (μGy/h){{cite web "On a Montreal-Fredericton flight in October, 1976, we measured the dose rate with a sensitive radiation monitor. The results are given in Figure 3.1. As you can see, the ground level dose rate was about 0.10 μGy/h; whereas, at the maximum flight altitude (8.8 krn or 29,000 ft), it was about 2.0 μGy/h. The total excess dose for the Montreal to Frederickton flight is only 0.7 μGy."

Dose and dose rate are used to measure different quantities in the same way that distance and speed are used to measure different quantities. When considering stochastic radiation effects, only the total dose is relevant; each incremental unit of dose increases the probability that the stochastic effect happens. When considering deterministic effects, the dose rate also matters. The total dose can be above the threshold for a deterministic effect, but if the dose is spread out over a long period of time, the effect is not observed. Consider the sunburn, a deterministic effect:{{cite web |url=https://canteach.candu.org/_layouts/15/WopiFrame.aspx?sourcedoc=/Content%20Library/20051603.pdf&action=default | author=J U Burnham | publisher=Chulalongkorn University |title=Radiation Protection, Chapter 4 | page=2 | year=1992 when exposed to bright sunlight for only ten minutes at a high UV Index, that is to say a high average dose rate,{{cite web |url=https://www.epa.gov/sites/default/files/documents/uviguide.pdf | publisher=United States Environmental Protection Agency |title=A Guide to the UV Index|year=2004|quote= "A radiative transfer model determines the flux of UV radiation for a range of wavelengths. An action spectrum weights the response of the human skin to UV radiation at each wavelength. Once weighted, the flux values are integrated over the entire range, resulting in an erythemal dose rate — the instantaneous amount of skin-damaging radiation reaching the surface"}} the skin can turn red and painful. The same total amount of energy from indirect sunlight spread out over several years - a low average dose rate - would not cause a sunburn at all, although it may still cause skin cancer.