A radiation detector is used in a well-logging tool for positioning in a wellbore of a geologic formation. The radiation detector includes a photomultiplier housing and a scintillator housing. A housing coupler joins together opposing ends of the photomultiplier housing and scintillator housing. A photomultiplier is contained within the photomultiplier housing and a scintillator body is contained within the scintillator housing. A scintillator window is secured to the housing coupler.