Characterization of a defective PbWO4 crystal cut along the a-c crystallographic plane: structural assessment and a novel photoelastic stress analysis

TL;DR

This study characterizes a defective PbWO4 crystal cut along the a-c plane, using XRD, EDS, and a novel photoelastic method to assess structural integrity and stress distribution, revealing inhomogeneities and compositional deviations.

Contribution

It introduces a new photoelastic analysis approach for crystals cut along the a-c plane and provides detailed structural and stress characterization of a defective PbWO4 crystal.

Findings

Detected deviations from nominal lattice dimensions due to Pb and W presence.

Revealed strong inhomogeneity in the crystal sample.

Validated the proposed photoelastic procedure for crystal stress analysis.

Abstract

Among scintillators, the PWO is one of the most widely used, for instance in CMS calorimeter at CERN and PANDA project. Crystallographic structure and chemical composition as well as residual stress condition, are indicators of homogeneity and good quality of the crystal. In this paper, structural characterization of a defective PbWO4 (PWO) crystal has been performed by X-ray Diffraction (XRD), Energy Dispersive Spectroscopy (EDS) and Photoelasticity in the unusual a-c crystallographic plane. XRD and EDS analysis have been used to investigate crystallographic orientation and chemical composition, while stress distribution, which indicates macroscopic inhomogeneities and defects, has been obtained by photoelastic approaches, in Conoscopic and Sphenoscopic configuration. Since the sample is cut along the a-c crystallographic plane, a new method is proposed for the interpretation of the fringe pattern. The structural analysis has detected odds from the nominal lattice dimension, which can be attributed to the strong presence of Pb and W. A strong inhomogeneity over the crystal sample has been revealed by the photoelastic inspection. The results give reliability to the proposed procedure which is exploitable in crystals with other structures.