Ab initio calculation of optimum absorber thickness in M'ossbauer spectroscopy

The aim of study is to optimize the Mossbauer experiment parameters. The main criterion for optimization is the quality of the experimental spectrum SNR, which is determined by the signal to noise ratio S / N. One of the most important parameters affecting on the quality of the spectrum is the absorber thickness. The introduction of the article is devoted to the theoretical consideration of the influence of the absorber thickness on the quality of spectrum. Analysis of the theoretical dependence of the shape of the spectrum allowed us to propose the technique of choosing the optimal thickness, based on the ab initio calculation of the transmission integral. On the basis of the proposed technique were calculated the optimum thickness for the model samples, which have spectra with different hyperfine structure and the different contributions of non-resonant absorption. When selecting the chemical composition of model samples the main attention was paid to the influence of matrix effects. These effects are directly depend from the ratio of resonant to nonresonant atoms in the absorber. The experimental part of the project was dedicated to test the theoretically predicted optimum absorber thickness with real ones. We measured the number of Mössbauer spectra of synthesized samples with different thicknesses. The results of these measurements were plotted as dependence of the experimental spectrum quality with the absorber thickness. Experimentally found optimum thickness values coincided with the theoretically calculated one. It was shown that the optimum thickness depends strongly on the matrix in which the resonance isotopes are placed. In the case of heavy matrix with a high influence of non-resonant absorption the optimum thickness of the absorber shifts towards lower values. The presence of background only reduces the absolute values of the signal / noise ratio and does not affect on the position of the maximum.