A detector for detecting ionizing radiation comprises a scintillator 10 selected to emit light in response to incidence thereon of radiation to be detected, at least one detector 16 for detecting said emitted light, and at least one optical waveguide 12 for transmitting said emitted light to said detector 16. The optical waveguide typically comprises a flexible solid or hollow fiber that can be incorporated into a flexible mat or into a fiber-reinforced structure, so that the detector is integrated therewith.