The invention provides a fluoride single crystal for detecting radiation having high luminescence intensity, a scintillator, a radiation detector employing the single crystal and a method for detecting radiation. The fluoride single crystal for detecting radiation contains Ce and at least one element (R.sup.1) of Lu and Gd, wherein the single crystal is represented by Ce.sub.1-xR.sup.1.sub.xF.sub.3 (0.001.ltoreq.x.ltoreq.0.5).