Which statement best differentiates deterministic radiation effects from stochastic effects?

• A. Deterministic effects have a threshold and severity increases with dose; stochastic effects have no true threshold and probability increases with dose.
• B. Deterministic effects occur only at very high doses; stochastic effects occur at any dose with fixed probability.
• C. Deterministic effects are caused by internal contamination; stochastic effects are caused by external exposure.
• D. Deterministic effects have no dose threshold; stochastic effects have a fixed threshold.

Answer: (B)

The key idea is how dose relates to outcomes. Deterministic effects show a clear threshold: below a certain dose they don’t occur, and once you pass that threshold the severity grows with the dose. Stochastic effects have no true threshold—the chance that they will occur increases as the dose goes up, while the severity of a given event isn’t tied to the dose in the same direct way. So a statement that signals a threshold for deterministic effects and that stochastic effects can occur at any dose with a risk that increases with dose best captures the main difference. Note that in practice the probabilistic nature of stochastic effects isn’t “fixed”; the probability rises with dose, rather than being the same at all doses. The other options either misstate the threshold concept or mix up exposure types.