What characteristic is associated with a non-linear graph in radiation dose response?

A non-linear graph in radiation dose response indicates that responses are not proportional to the dose of radiation received. This means that as the dose increases, the biological effect does not increase in a simple, direct manner; rather, the relationship can exhibit complex characteristics where small changes in dose can lead to varying responses.

In a non-linear response, certain thresholds may exist, where certain doses do not elicit a response, or there may be saturation points where additional doses produce diminishing returns in response. This type of behavior is important to understand in radiation safety and risk assessment, as it informs medical professionals and researchers about how biological systems react to different levels of radiation exposure.

The other options suggest characteristics that are inconsistent with a non-linear response. For instance, a direct proportionality of responses to dose or a steady increase in response with dose would imply a linear relationship, which does not align with the nature of non-linear responses. Also, the idea that responses occur only at high doses does not necessarily signify a non-linear relationship, as non-linear responses can manifest at various dosages depending on the biological system in question.