What characterizes an acute radiation dose?

An acute radiation dose is defined by the delivery of a high dose of radiation over a short period of time. This type of exposure can lead to significant biological effects and symptoms of acute radiation syndrome, as the body does not have enough time to repair the damage caused by the radiation before more is received. The severity of the symptoms will often depend on the amount of radiation exposure and the speed at which it occurs.

In contrast, the other options describe scenarios that do not fit the definition of an acute radiation dose. Receiving radiation over a long period characterizes chronic exposure, which leads to different health implications compared to acute exposure. Small doses over time also contribute to cumulative radiation exposure, but again, do not qualify as acute. Lastly, the statement about only affecting external skin layers is misleading, as acute radiation exposure can damage internal organs and tissues beyond just the skin.