residual radiation

Residual radiation refers to radiation emitted more than one minute after a nuclear detonation. This radiation primarily originates from the weapon's debris. If the explosion occurs on or near the surface, soil and other materials are drawn into the rising cloud, leading to both early and delayed fallout.1

Early fallout settles within 24 hours, posing an immediate biological hazard and potentially contaminating large areas. Delayed fallout consists of microscopic particles dispersed by winds, settling in low concentrations globally. Nuclear explosions produce over 300 different isotopes, with half-lives ranging from fractions of a second to millions of years. The total radioactivity decreases rapidly; after seven hours, it's about 10% of the one-hour level.1