Thickness determination of material plates by gamma-ray transmission technique using calibration curves constructed from Monte Carlo simulation

This paper presents a new approach for determining the thickness of material plates by gamma-ray transmission technique using calibration curves obtained from simulated spectra through the Monte Carlo algorithm. The narrow transmitted gamma-ray beam from a collimated source of 137Cs (with the energy of 661.7 keV) for different thicknesses of the metal plates (aluminum, copper, and steel) was recorded by a NaI(Tl) detector. Besides, the Monte Carlo simulations of radiation transport in a model with the same geometry, source, and detector characteristics as in the real experiment were performed to obtain the transmission spectra. A good agreement between the experimental and simulated spectra was observed. The linear calibration curves of the value of ln(R) versus the thickness of material plates were constructed using Monte Carlo simulated data (R is the ratio of the area under a transmitted peak for measurement with sample relative to that for measurement without sample). The unknown thickness of a sample was determined by substituting the experimental value of ln(R) into the linear calibration curve corresponding to such sample. Besides, the range of measurable thickness with the desired accuracy was estimated for each material based on simulated data. The obtained results showed excellent quantitative values even without using any standard plate with known thickness for the calibration.