A dose rate is quantity of radiation
absorbed or delivered per unit time.
It is often indicated in
micrograys per hour (µGy/h)
or as an
equivalent dose
Equivalent dose is a dose quantity '' H '' representing the stochastic health effects of low levels of ionizing radiation on the human body which represents the probability of radiation-induced cancer and genetic damage. It is derived from the ...
rate Ḣ
T in rems per hour (rem/hr) or
sievert
The sievert (symbol: SvNot be confused with the sverdrup or the svedberg, two non-SI units that sometimes use the same symbol.) is a unit in the International System of Units (SI) intended to represent the stochastic health risk of ionizing radi ...
s per hour (Sv/h).
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:
when exposed to bright sunlight for only ten minutes at a high UV Index, that is to say a high average dose rate,
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.
References
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