What type of radiation occurs within the first 90 seconds of a blast?

Initial radiation is the correct response because it refers specifically to the types of radiation emitted during the first 90 seconds following a nuclear explosion. This period is characterized by a release of gamma rays and neutrons resulting from the explosion, which can cause immediate harm to living organisms in proximity to the blast site. This initial burst of radiation is significant because it contributes to the immediate radiation exposure and effects on the environment and individuals.

In contrast, residual radiation pertains to radiation that remains in the aftermath of a nuclear explosion, while delayed radiation involves effects that manifest later, often due to fallout. Long-term radiation refers to ongoing exposure risks from radioactive materials that persist in the environment over an extended period. Understanding this distinction is essential for recognizing the immediate dangers posed by a nuclear incident compared to long-term environmental and health concerns.