Which type of burst is associated with the worst fallout due to its interaction with the ground?

A surface burst is associated with the worst fallout due to its interaction with the ground because it detonates directly on or very near the surface. This type of explosion causes a large amount of earth and debris to be vaporized and lofted into the atmosphere, where it can condense and form radioactive particles. These particles, along with the fallout from the explosion itself, can spread over a wide area due to wind and weather patterns.

In contrast, an airburst occurs when a weapon detonates in the air, which minimizes ground interaction and reduces the amount of fallout. Although underwater bursts can also produce fallout, their effects are generally contained within the water, leading to less widespread contamination compared to surface bursts. Shallow underwater bursts can create more localized damage but still generate less fallout than a direct surface explosion. Deep underwater bursts primarily result in a powerful underwater shockwave with limited fallout impact on land.

Thus, surface bursts are especially dangerous from a fallout perspective due to their significant potential to contaminate large areas with radioactive debris.