Scintillator Crystals: Structure, Characterization and Models for Better Performances

Abstract

The majority of instrumentation and systems for radiation detection are based on scintillators. Scintillating materials convert high-energy radiation in visible light (visible photons), this light is collected by a photomultiplier and elaborated to obtain information about incident radiation energy spectra and for image reconstruction. Among the variety of scintillating substances and forms, the scintillating crystals offer the best performances in various fields of application. Medicine, Physics, Industry, Earth and Soil science, Aerospace, Astronomy applications and others, require more and more sophisticated and accurate tools to face new and deeper challenges. In this direction, the development of new materials and the improvement of the existing ones is mandatory. A deeper knowledge of the crystal physics as well as all the mechanisms relative to their scintillating behaviour is crucial to accomplish the needs of these applications. Theories and simulations are fundamental to obtain predictive models. Further to these, accurate testing procedures and quality control methodologies play a major role in monitoring the crystal condition and improving the production processes, helping the producers of crystals to enhance the process efficiency and allowing crystals' "end users" to have better performing devices.Medical instrumentation, for diagnostics and imaging, requires high sensitivity, in addition to a fast and reliable response, thereby reducing health risk and increasing both the spatial and time resolution. The different bio-medical instrumentation spans from the PET, to the high-resolution SPECT and Gamma camera, including X-Ray imaging [1]; therefore, each crystal species must be optimized for the relevant purpose.However, security and geological instrumentation require another kind of scintillating crystal, which is durable and stable over time.The design and construction of calorimeters for high-energy physics studies are critical in scintillator development. It is opportune to emphasize the discovery of the Higg's boson at CERN by CMS calorimeter, where about 80,000 large-dimension PbWO 4 (PWO) were used. For the first time, a large-scale production of big crystals (2 cm × 2 cm × 20 cm) was necessary [2,3]. Moreover, the large production scale called for a fast and non-destructive quality control to avoid, among the other quality requirements, the risk of fracture due to internal stress [4]. The implementation of in-line quality control using a fast and non-destructive technique is mandatory for all of the above applications. The different applications have specific requirements, since scintillators must be able to detect photons at different energies. For example, energy detected by PWO crystals at CMS is of the order of 100 Gev and the photon energy for X-Ray imaging decreases down to 20 KeV. Different scintillator parameters are crucial for determining the efficiency and accuracy of detection systems. Among them, we cite some significant parameters such as the following: the Light Yield

Growth and Scintillation Properties of Directionally Solidified Ce:LaBr3/AEBr2 (AE = Mg, Ca, Sr, Ba) Eutectic System

“…Scintillators coupled with photodetectors are widely used in radiation imaging applications such as medical imaging, security, high-energy physics, astrophysics, oil well logging, etc. In order to meet the needs of these applications, a deeper knowledge of crystal physics and all the mechanisms involved in their scintillating behavior is important [1]. In conventional high-resolution radiation imaging systems employing inorganic scintillators, scintillation light must be guided to photo-sensors efficiently without lateral light diffusion [2].…”