Device for measuring the thickness of layers with a radionuclide irradiating the layer

Claim 1

A device for measuring the thickness of layers of solid materials, such as of thin metal layers on a carrier layer of another metal, by the Beta ray backscatter method, comprising a radionuclide irradiating the layer, which radionuclide produces radiation whose energy corresponds to the thickness of the layer, each radionucilide/layer material and if present, carrier material- combination defining a special test problem. a detector which receives the backscatter radiation, which comes from the layer and a possibly present carrier material and produces at its output a pulse count, X, in the region between a lower first count X 0 corresponding to the backscatter associated with zero layer thickness, and an upper count X s associated with the range of an infinitely thick layer, and a digital computing means connected to said detector, said digital computing means comprising means for dividing the difference between the detected pulse count, X, and the lower first count, X 0 , by the difference between the upper pulse count, X s and the lower first pulse count X O , to calculate from the output pulse count from the detector a normalized pulse count ##EQU4## wherein: said digital computing means is connected to a digital to analog converter and said digital to analog converter is connected to an analog correction circuit, having a permanently wired portion, said correction circuit realizing a function X n corr = X n + A [ a 2 X n p (1-X n ) q ]and generating an output signal in proportion to this function, and wherein an indicator instrument for receiving said analog signal from the correction circuit corresponding to X n corr and having an interchangeable, non-linear scale calibrated in thickness with respect to the special test problem, and means for externally setting the magnitude A of the correction function are provided, where A is a dimensionless number between + 1 and -1, a 2 is a dimensionless number between + 0.1 and -0.1, p and q are dimensionless positive values substantially between 0.5 and 1.5 but different from one another, and which are realized by said permanently wired porition of the correction circuit.

Claim 2

A device for measuring the thickness of layers of solid materials, such as of thin metal layers on a carrier layer of another metal, by the Beta ray backscatter method, comprising a radionuclide irradiating the layer, which radionuclide produces radiation whose energy corresponds to the thickness of the layer, each radionucilide/layer material and if present, carrier material- combination defining a special test problem. a detector which receives the backscatter radiation, which comes from the layer and a possibly present carrier material and produces at its output a pulse count, X, in the region between a lower first count X 0 corresponding to the backscatter associated with zero layer thickness, and an upper count X s associated with the range of an infinitely thick layer, and a digital computing means connected to said detector, said digital computing means comprising means for dividing the difference between the detected pulse count, X, and the lower first count, X 0 , by the difference between the upper pulse count, X s and the lower first pulse count X O , to calculate from the output pulse count from the detector a normalized pulse count ##EQU4## wherein: said digital computing means is connected to a digital to analog converter and said digital to analog converter is connected to an analog correction circuit, having a permanently wired portion, said correction circuit realizing a function X n corr = X n + A [ a 2 X n p (1-X n ) q ]and generating an output signal in proportion to this function, and wherein an indicator instrument for receiving said analog signal from the correction circuit corresponding to X n corr and having an interchangeable, non-linear scale calibrated in thickness with respect to the special test problem, and means for externally setting the magnitude A of the correction function are provided, where A is a dimensionless number between + 1 and -1, a 2 is a dimensionless number between + 0.1 and -0.1, p and q are dimensionless positive values substantially between 0.5 and 1.5 but different from one another, and which are realized by said permanently wired porition of the correction circuit.