X-ray apparatus for examination of an object 30 in the form of tissue, for example, the female breast, which is compressed between two plates 11, 15. The radiation passing through the tissues is registered by a radiation detecting arrangement 29 containing a film plate or the like, and is measured by a measuring arrangement 27 which contains a measuring cell 28. The output signal of the measuring arrangement 27 is taken to a disconnection element 32 for interrupting the irradiation after a particular measured quantity of radiation. Both the radiation detecting arrangement 29 and the measuring arrangement 27 have a sensitivity which varies with the frequency, and the variation in the sensitivity of both arrangements as a function of frequency is also different. When objects 30 with different thickness are irradiated, the frequency content of the radiation arriving at the radiation detecting arrangement 29 and the measuring arrangement 27 will vary, more specifically, such that the thicker the object the more the frequency spectrum of the transmitted radiation is shifted upward in frequency. As a result of the fact that the two arrangements have different frequency sensitivity, a deviation is produced that varies with the object's thickness between the measured quantity of radiation and the quantity of radiation received by the radiation detecting arrangement 29, and if the output signal of the measuring arrangement 27 is used alone to actuate the disconnection element 32, the disconnection would occur at different quantity of radiation received for objects of different thickness. In order to offset this, there is a measurement transmitter 23 which measures the distance between said plates 11, 15 and puts out a signal representative of the measured distance, which signal in combination with the output signal of the measuring arrangement 27 can influence the disconnection element 32 in such a way that said varying deviation between the measured quantity of radiation and the actually received quantity of radiation is compensated and disconnection occurs after a given received radiation quantity, regardless of the thickness of the object, figure 2. IMAGE
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