The interpretation of detector response to changes in a subcritical reactor is at present only qualitatively understood. In an experimental facility the detectors can be moved until adequate response is obtained. However, in a nonexperimental facility which lacks the flexibility to relocate detectors, it may not be possible to correlate changes in Ke with observed changes in detector response. In this article, a calculation model and method are derived and tested permitting quantitative interpretation of detector response to material and geometric changes in a subcritical reactor.