The basic working principle of the β-ray backscattering method is to use radioactive isotopes to release β-rays. After the β-rays are irradiated to the test sample, a part of the β -rays entering the metal are reflected to the Detector. The intensity of the reflected beta particles is a function of the type and thickness of the coating being measured. Therefore, the thickness of the measured coating can be measured by measuring the "ray intensity" reflected by the measured coating from the Detector.
The β-ray backscattering method can measure the thickness of metal and non-metal coatings on metal or non-metal substrates, but it is mainly used to measure the thickness of thin (less than 2.5 μm) noble metal coatings.
The measurement error is within ±10%. The greater the difference between the atomic numbers of the covering layer and the base material, the higher the measurement accuracy. ISO3543-81 requires that the difference between the atomic number of the substrate and the coating should not be less than 5. For materials with an atomic number below 20, this difference can be reduced to 25% of the higher atomic number; for materials with an atomic number higher than 50, this difference is at least 10% of the higher atomic number. Because "the Thickness Gauge itself is only a comparative instrument for measuring the backscattering intensity, its thickness scale is obtained through the calibration of the standard sample, if the coating composition, density, matrix material, surface curvature of the tested sample and the standard sample If there is a difference, the thickness reading should be corrected according to the following formula:
The disadvantage of this method is that various radioactive sources are used, which is harmful to human health. The operator should have the necessary protective measures, and the cost of the instrument is also relatively high.
