The invention relates to a device for measuring local absorption differences in a cross-section of an object. The device comprises at least one detector which has a gas-filled chamber. In the chamber are arranged, at a comparatively small distance from each other, a high voltage electrode and a signal electrode. A high voltage source is connected to the high voltage electrode and a signal measuring circuit is connected to the signal electrode.
A device of this kind, in the form of an X-ray scanner comprising a series of detectors which can be read separately is known from U.S. Pat. No. 4,048,503. In an apparatus of this kind, movement of the detectors with respect to the object to be examined causes vibrations which result in microphonic interference signals in the detector signal to be measured.
Because of the construction of the detector elements--a high voltage electrode and an adjacent signal electrode which are mounted at a short distance from each other--each measuring chamber constitutes a capacitor whose capacitance is modulated by vibrations of the electrodes. This modulation causes an interference signal in the measuring signal. It has been found that this capacitance modulation is not adequately mitigated even by specially mounting the various electrodes.