Final answer:
Nausea and vomiting within the first 10 minutes of radiation exposure indicate a potentially deadly dose, due to the sensitivity of rapidly reproducing cells in the digestive system.
Step-by-step explanation:
The symptom that signifies a potentially deadly dose of radiation exposure within the first 10 minutes is the immediate onset of nausea and vomiting, as it indicates a severe systemic impact on the body, particularly the gastrointestinal system.
Such a response is due to the high sensitivity of the cells lining the digestive system, as they rapidly reproduce and are therefore more vulnerable to damage from high doses of radiation.
A single, short-term exposure to a large amount of radiation can lead to multiple health effects, ranging from a change in blood count to a collapse of the central nervous system, with the most severe outcomes including death.