Quality Control and Structural Assessment of Anisotropic Scintillating Crystals

Abstract

Nowadays, radiation detectors based on scintillating crystals are used in many different fields of science like medicine, aerospace, high-energy physics, and security. The scintillating crystals are the core elements of these devices; by converting high-energy radiation into visible photons, they produce optical signals that can be detected and analyzed. Structural and surface conditions, defects, and residual stress states play a crucial role in their operating performance in terms of light production, transport, and extraction. Industrial production of such crystalline materials is a complex process that requires sensing, in-line and off-line, for material characterization and process control to properly tune the production parameters. Indeed, the scintillators’ quality must be accurately assessed during their manufacture in order to prevent malfunction and failures at each level of the chain, optimizing the production and utilization costs. This paper presents an overview of the techniques used, at various stages, across the crystal production process, to assess the quality and structural condition of anisotropic scintillating crystals. Different inspection techniques (XRD, SEM, EDX, and TEM) and the non-invasive photoelasticity-based methods for residual stress detection, such as laser conoscopy and sphenoscopy, are presented. The use of XRD, SEM, EDX, and TEM analytical methods offers detailed structural and morphological information. Conoscopy and sphenoscopy offer the advantages of fast and non-invasive measurement suitable for the inspection of the whole crystal quality. These techniques, based on different measurement methods and models, provide different information that can be cross-correlated to obtain a complete characterization of the scintillating crystals. Inspection methods will be analyzed and compared to the present state of the art.

Photoelastic Properties of Trigonal Crystals

“…Comparison of these sums of POC with the analogous ones for principal coefficients π im determined on the direct cut sample makes it possible to confirm the reliability of the POC values as well as piezo-optical identity of the samples cut from the different parts of crystal boule or from different boules. It should be noted that the polarization-optical (see, e.g., [16][17][18][24][25][26][27]) and conoscopic [28][29][30][31][32][33] methods are sometimes used for investigations of crystal photoelasticity. However, in this paper, the photoelasticity of lithium tantalate is solely studied using the interferometric technique.…”

“…It should be noted that the polarization-optical (see, e.g., [16][17][18][24][25][26][27]) and conoscopic [28][29][30][31][32][33] methods are sometimes used for investigations of crystal photoelasticity. However, in this paper, the photoelasticity of lithium tantalate is solely studied using the interferometric technique.…”

Расчет Остаточных Напряжений При Коноскопических Измерениях В Профилированных Монокристаллах Сапфира

“…При высоком уровне остаточных напряжений возможно растрескивание кристаллов при остывании или при их разрезке. Показано, что, целенаправленно изменяя конфигурацию тепловых экранов в ростовой зоне выращивания сапфировых лент, можно понижать уровень термопластических, а значит и остаточных напряжений в кристаллах [27][28][29][30].…”

Untitled

“…where n i are the principal refraction indexes, σ i are the principal values of the stress tensor T , and f iso is the photoelastic constant for isotropic materials which depends on the components of the piezooptic tensor and on the refraction index n o of the unstressed material Such a relation, obtained for the first time by David Brewster [1830] in 1818 and accordingly known as the "Brewster law", is at the basis of the experimental stress analysis based on photoelasticity. Besides the classical field of application in experimental structural mechanics (viz., [Kuske and Robertson 1974;Bain 2019]) such a relation allows, for instance, for the characterization and the quality control of high-energy physics crystals like the ones used in the CMS calorimeter at CERN or in the PANDA experiment at GSI in Darmstadt (viz., the recent review in [Montalto et al 2019]).…”