Study of Surface Roughness of CsI:Tl Crystals Treated by Various Abrasives

The study of the surface roughness of CsI:Tl scintillators processed by abrasives with different grain size was performed to obtain the surface characteristics that are important for simulation of light collection processes in scintillators. The degree of roughness of the surface was studied qualitatively, by optical microscopy, and quantitatively, by measuring reflectance distribution functions at different angles of light incidence on the samples. Micrographs of the sample surfaces, obtained by means of optical microscopy, allowed the estimation of the typical roughness for each abrasive. The micro-facet slope distribution functions were extracted from the measured reflectance distribution. It was found that these functions depend mainly on the grain size of the abrasive. For the same abrasive, the micro-facet slope distribution functions do not depend on the incidence angle, which is a good demonstration of the reliability of the results. To demonstrate how the variation of the surface roughness influences the light collection, the pulse-height spectra of the scintillator samples with different surface treatments were measured. Micro-facet slope distributions obtained for CsI:Tl can be used for the simulation of light collection processes in different scintillators with similar hardness and elastic properties.