DEVICE FOR MEASURING THE THICKNESS OF METALLIC LAYERS UTILIZING BETA RAY BACKSCATTERING

摘要

A device for measuring thickness of layers when a radioactive nuclide bombards the layer to produce an irradiation having an energy level corresponding to the thickness of the layer. A detector absorbs radiation backscattered from the layer and possibly from a carrier material if present, and produces output pulses at a rate between that corresponding to a layer of zero thickness and that corresponding to a quasi-endlessly thick layer. An integration stage coupled to the output of the detector produces a voltage proportional to the rate of pulses from the detector. A voltage compensation stage connected to the integration stage output produces a voltage equal to and opposite in sign with respect to the output voltage of the integration stage, which corresponds to the pulse rate of the backscattering pertaining to the zero thickness of the layer. The output voltages of the integration and voltage compensation stages are conducted at a common point which, in turn, is connected with a network controllable in its transmission gain and loss. The network is connected with an equalizer for linearizing a mathematical function which represents a family of calibration curves correlating thickness with measured backscattering. A recording device connected to the equalizer amplifier permits readings of layer thickness to be obtained.