Generally, at or below how many rads will full-body x-radiation exposure show no injury with ordinary methods?

• A. 25
• B. 75
• C. 100
• D. 200

Answer: (A)

The idea being tested is the dose at which whole-body radiation starts to cause observable injury. The body can repair small, sublethal damage from radiation, and with acute exposure, there’s a threshold below which no injury is expected to show up with ordinary methods. That threshold is about twenty-five rads. So full-body exposure at or below this level typically does not produce clinical injury. Doses higher than that increase the risk of hematologic effects and other signs of radiation stress, with greater likelihood as the dose rises. The other options represent doses high enough that injury would be expected more often, so they are not the correct threshold.