Final answer:
Biological material is most sensitive to high radiation doses received in a short time. Studies with fruit flies and mice suggest that spread-out low doses are less damaging. Mice studies, especially, indicate that repair mechanisms help mitigate effects of low doses spread over time.
Step-by-step explanation:
Biological material is most sensitive to irradiation under the condition of high radiation dose received over a short period of time. This principle is supported by studies that show rapidly dividing cells, such as those found in bone marrow, intestinal tissue, hair follicles, and reproductive organs, are most affected by irradiation.
Consequently, these are the tissues that are typically damaged during whole-body exposures to radiation. Long-term exposure studies indicate that the number of genetic defects increases with both the magnitude of the dose and the exposure time.
For instance, fruit flies exhibit a linear relationship between genetic defects and exposure. In contrast, mice show a lower number of defects when radiation is spread out over time due to their bodies' repair mechanisms. Since mice are biochemically more similar to humans, this model might apply to humans as well, suggesting that spread-out low doses of radiation are less damaging than concentrated high doses. Moreover, radiation protection measures emphasize minimizing exposure time, keeping a safe distance, and using shielding to reduce irradiation.