Time

The mixture of radionuclides in the fission products formed after a nuclear detonation is so complex that it is not possible to represent their decay in terms of a single half-life. However, it has been found that for every sevenfold increase in time after a nuclear explosion, the relative activity decreases by a factor of ten.

As shown, 1 hour after detonation is used as a reference point and assigned a relative activity of 100 percent. At 7 hours after detonation, the relative activity decreases to 10 percent. If this curve were extended, it would show that, at 49 (7x7) hours after detonation, the relative activity decreases to 1 percent and that, at 2 weeks (7x7x7 hours), it is 1/10 of 1 percent.