**Core Concept**
The question tests the concept of the **LD50/30**, which is the dose of ionizing radiation that is lethal to 50% of exposed individuals within 30 days. This concept is essential in radiology to estimate the severity of radiation exposure and predict the likelihood of radiation-related mortality.

**Why the Correct Answer is Right**
The correct answer, **D. 4-6 weeks**, is based on the fact that a dose of 5 Gy (500 rads) is considered a high-dose radiation exposure. The LD50/30 is generally accepted to be around 4-6 Gy, which means that a dose of 5 Gy would be expected to kill approximately 50% of exposed individuals within 30 days. This is because high doses of radiation cause significant damage to the bone marrow, gastrointestinal tract, and central nervous system, leading to severe symptoms and death.

**Why Each Wrong Option is Incorrect**
**Option A:** A dose of 5 Gy would not cause immediate death, as the onset of symptoms and mortality occurs within days to weeks, not hours.
**Option B:** While a dose of 5 Gy is lethal, it is not sufficient to cause death within 1 week, as the body's natural repair mechanisms can temporarily mitigate the effects of radiation.
**Option C:** A dose of 5 Gy is not sufficient to cause death within 2-3 weeks, as the body's natural repair mechanisms and the development of radiation sickness symptoms would take longer to manifest.

**Clinical Pearl / High-Yield Fact**
The **Radiation Emergency Assistance Center/Training Site (REAC/TS)** recommends that individuals exposed to high-dose radiation receive immediate medical attention, including administration of potassium iodide to prevent thyroid damage and radiation sickness.

**✓ Correct Answer: D. 4-6 weeks**