The Central Nervous System threshold is equal to how many Gy?

• A. 10
• B. 20
• C. 30
• D. 40

Answer: (B)

The idea being tested is the dose at which CNS damage becomes likely after a very high, one-time exposure. This threshold is about 20 Gy for the central nervous system. Below this level, acute CNS symptoms are unlikely from a single rapid exposure; at or above it, you can see severe neurological effects such as confusion, ataxia, seizures, coma, and potentially death if the exposure is whole-body. This is a deterministic effect, meaning it has a clear dose threshold and severity increases with dose. It’s different from stochastic effects (like cancer risk), which don’t have a fixed threshold and rise with dose. So, for a single acute exposure to the CNS, around 20 Gy is the established threshold.