The invention relates to a radiometric measuring device for measuring a physical measurement variable, in particular a filling level or a density, of a filling material (1) in a container (3) and / or for monitoring whether the physical measurement variable exceeds or falls below a preset limiting value by way of a radioactive emitter (5) which, during operation, sends radioactive radiation throughthe container (3), and by way of a detector (7) which is arranged at a side of the container (3) opposite to the emitter (5) and which is used for detecting a radiation intensity which depends on thephysical measurement variable and penetrates the container (3) and for converting said radiation intensity into an electrical output signal, by means of said measuring device a very accurate measurement of the radiation intensity can be performed in a region that is located within the measurement range of the detector (7) and that can be defined in a very flexible manner. To this end, a detector (7) is provided which has a support (9, 37) onto which at least one scintillation fiber (11) is coiled which converts impinging radiometric radiation into light flashes, the light of which spreads toward the ends (E1, E2) of the respective scintillation fiber (11), the support comprising at least one array (13, 13') of avalanche photo diodes (APD) which are operated according to the Geiger mode and which convert impinging light into an electrical signal, at least one end (E1, E2) of each scintillation fiber (11) being connected to avalanche photo diodes (APD) of an array (13, 13'), the supportfurther comprising measuring device electronics that are connected to the avalanche photo diodes (APD) and generate the electrical output signal on the basis of the electrical signals provided by theavalanche photo diodes (APD).