By Matthew Moulson (LNF-INFN), project spokesperson. Edited by Rickard Stroem (DESY)
High-performance electromagnetic calorimeters often make use of inorganic crystal scintillators. Their high density makes them well suited for the construction of large homogeneous detectors where the scintillating material simultaneously serves as both absorber and active detector medium. An appropriate choice of inorganic crystal can provide both high light yield and fast light emission, resulting in optimal energy resolution. The main drawback is their high cost. Plastic scintillators constitute an economical alternative and provide relatively high light yield and fast timing, but the lower density generally brings about an inferior energy resolution. The AIDAinnova blue-sky project “NanoCal” will lay the ground for a new generation of fine-sampling calorimeters fulfilling the role of large-volume homogenous detectors at a fraction of the cost. These make use of innovative scintillating materials based on perovskite or chalcogenide nanocrystals dispersed in a plastic matrix to form a Nano-Compostite (NC) scintillator. Figure 1 shows a perovskite nanocomposite scintillator plate during manufacture.
Figure 1: Perovskite nanocomposite scintillator during manufacture. Credit: Glass To Power S.p.A.
With O(100 ps) light decay times and O(1 MGy) radiation tolerance these materials are ideal candidates for the construction of economical, high-performance fine-sampling devices for calorimetry and high-efficiency photon detection. Indeed, NC scintillators have been the focus of much attention in the materials-science community, but almost no studies have been done on the response of NC scintillators to high-energy particles. Within the “NanoCal” project, prototypes will be constructed using both conventional and NC scintillators, allowing for a direct comparison of the performance gains with NC scintillators.
The project brings together the experience at INFN, in the design and construction of fine-segmented electromagnetic calorimeters, with the expertise in the synthesis of nanoparticles and production of nanocomposite scintillators from Glass To Power S.p.A. of Rovereto, Italy, a spin-off company for the commercialization of nanocomposite scintillator technology for solar power generation. The prototypes will be tested in beam tests at the Frascati Beam-Test Facility and the North Area test-beam facility at the CERN SPS. Material characterization and test-beam measurements will be carried out in synergy with the activities of the AIDAinnova partners in “WP8: Calorimeters and Particle Identification Detectors”, working on innovative crystal calorimetry.
Figure 2: First prototypes of shashlyk calorimeter tiles made with perovskite nanocrystals. Produced at Glass To Power S.p.A. Credit: Matthew Moulson.
One of the most promising aspects of the use of NC scintillators is that the nanocrystals and the composites can be engineered to meet specific performance requirements in terms of emission time, wavelength and light yield. Areas of optimization include increasing the concentration of the nanocrystal sensitizer while maintaining uniformity and optical quality, decreasing the emission time, and increasing the transparency of the composite to scintillation light. Increased concentrations of high-Z sensitizer result in higher sampling fraction, better energy resolution, higher detection efficiency, and more compact designs. The same principles can be used to develop Wavelength Shifting (WLS) materials to facilitate light readout. Optimization of the NC scintillator calorimeter prototypes along these lines, including the validation of the radiation resistance of the NC scintillator components, is an essential aspect of the research programme.
The development of innovative NC scintillators and WLS materials matching the performance of inorganic crystals will allow significant advances in detectors for calorimetry, tracking, and fast timing. In particular, applications are envisioned in large-volume detectors at future colliders such as the FCC, or in the nearer term, for high-rate, forward calorimetry for experiments such as NA62 and LHCb after future intensity upgrades. The technology can also be used to produce low cost, high performance radiation detectors for use in such disparate fields as observational astrophysics, diagnostic medical imagery, industrial control, geological survey, and nuclear security.