What source of acute radiation exposure poses the greatest risk to humans?

The source of acute radiation exposure that poses the greatest risk to humans is diagnostic imaging. Diagnostic imaging procedures, such as X-rays and CT scans, involve the use of ionizing radiation to create images of the body's internal structures. While these procedures are designed to provide valuable medical information, they can expose patients to significant doses of radiation, particularly with certain types of imaging studies that require multiple exposures or high radiation levels.

The risk associated with acute radiation exposure from these diagnostic procedures primarily comes from the potential for radiation-induced effects, including deterministic effects like skin burns or radiation sickness, when high doses are delivered in a short timeframe. In addition, there is also the cumulative risk of stochastic effects such as cancer development over time as exposure increases, which can be a concern with repeated imaging over a patient's lifespan.

Other sources of radiation exposure, such as environmental radiation and therapeutic radiation, do contribute to overall radiation exposure but typically do not match the acute risk associated with diagnostic imaging in terms of immediate health effects. Occupational exposure, while significant in the context of radiologic technologists and other medical professionals, generally occurs over prolonged periods and presents different risk profiles compared to the instantaneous exposure from diagnostic imaging procedures.