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How does initial radiation differ from residual radiation after a nuclear explosion?

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Atomic bomb — atomic bomb The first atomic bomb test, near Alamogordo, New Mexico, July 16, 1945.

Nuclear radiation from a detonation is categorized by the timing of its emission relative to the explosion.12

Initial Radiation

Also known as prompt radiation, this consists of gamma rays and neutrons produced within the first minute of detonation. While it accounts for only about 3 percent of the total energy released, it is highly hazardous to living organisms because it can penetrate most structures over considerable distances.1

Residual Radiation

Residual radiation is defined as radiation emitted more than one minute after the explosion. It primarily originates from the weapon debris and, in surface bursts, from soil and materials vaporized and lofted into the atmosphere. This material returns to Earth as fallout, which can cause widespread contamination. Unlike initial radiation, the intensity of residual radiation decreases over time due to radioactive decay, following a rule of thumb where the dose rate drops by a factor of 10 for every sevenfold increase in time after the detonation.3