Abstract: An alpha particle radiation probe which eliminates the need for any intermediate light coupling devices between the scintillation generating phosphor and scintillation detector while at the same time providing uniform response to alpha particles over a substantially larger area than has heretofore been possible on the order of 100 cm.sup.2 to 150 cm.sup.2. The structure is arranged to quickly replace a light blocking screen that has been damaged in use. Significant reductions in weight and cost are also achieved because of the simpler construction and the elimination of the light coupling devices heretofore used. The apparatus eliminates the need for a second small aperture probe detector for localizing radiation hot spots by providing aperture reducing means quickly attachable to and detachable from the scanning window to reduce its aperture and provide the hot spots detection function simply and inexpensively.