Radiometric measuring device designed for the measurement of a level or density of a medium located in a container, and/or designed to monitor the undershooting or overshooting of a predefined limit value for the level or the density, with - a radioactive emitter mounted on the exterior of the container, said emitter emitting radioactive radiation through the container during operation, and - a detector arranged on a side opposite the emitter on the outside of the container, said detector serving to receive radiation intensity, which depends on the level or the density and passes through the container, and to convert it to an electrical output signal, characterized in that the detector has a carrier (9, 37) on which at least one scintillation fiber is wound, said fiber converting the incident radiometric radiation into flashes of light whose light propagates in the scintillation fiber as far as the ends of the fiber (E1, E2), -- said detector comprising at least one array (13, 13') of avalanche photodiodes operated in Geiger mode, said photodiodes converting the incident light impacting on them into an electrical signal, --- wherein at least one end (E1, E2) of each scintillation fiber is connected to avalanche photodiodes of one of the arrays (13, 13'), and -- wherein the detector features a measuring device electronics module that is connected to the avalanche photodiodes and that generates the electrical output signal using the electrical signals of the avalanche photodiodes. - a radioactive emitter mounted on the exterior of the container, said emitter emitting radioactive radiation through the container during operation, and - a detector arranged on a side opposite the emitter on the outside of the container, said detector serving to receive radiation intensity, which depends on the level or the density and passes through the container, and to convert it to an electrical output signal, characterized in that the detector has a carrier (9, 37) on which at least one scintillation fiber is wound, said fiber converting the incident radiometric radiation into flashes of light whose light propagates in the scintillation fiber as far as the ends of the fiber (E1, E2), -- said detector comprising at least one array (13, 13') of avalanche photodiodes operated in Geiger mode, said photodiodes converting the incident light impacting on them into an electrical signal, --- wherein at least one end (E1, E2) of each scintillation fiber is connected to avalanche photodiodes of one of the arrays (13, 13'), and -- wherein the detector features a measuring device electronics module that is connected to the avalanche photodiodes and that generates the electrical output signal using the electrical signals of the avalanche photodiodes. -- said detector comprising at least one array (13, 13') of avalanche photodiodes operated in Geiger mode, said photodiodes converting the incident light impacting on them into an electrical signal, --- wherein at least one end (E1, E2) of each scintillation fiber is connected to avalanche photodiodes of one of the arrays (13, 13'), and -- wherein the detector features a measuring device electronics module that is connected to the avalanche photodiodes and that generates the electrical output signal using the electrical signals of the avalanche photodiodes.