File:Serious accident avoided rad dose.png

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This diagram depicts the effect of a well executed radiation protection plan after a nuclear accident. The y-axis shows dose rate H/t (~radiation level) that a population (e.g. of a city) is exposed to. The x-axis is time t. In the beginning natural background radiation is at level x. As the cloud of radioactive particles passes the population, a sharp rise in radiation level occurs at first, after which the radiation level settles down as the cloud leaves the area due to wind. With effective radiation protection measures, such as sheltering inside buildings, the dose rate that affects the population can be limited to level y, opposed to the high curve. Thus the high dose H sub A, marked with orange color, is averted. Rather the population gets the dose H sub B, marked in white, which is only slightly higher than then natural dose caused by dose rate x. The blue line marks the beginning of the effect of radiation protection measures while the red line marks the end.

Based on Mustonen, R. et al.: Ydinuhkat ja varautuminen, Säteilyturvakeskus, Helsinki, 1995, ISBN 951-712-058-3