YAG:Ce-based scintillation fibers were produced by ISMA

We are delighted to announce that a batch of 101 pieces of YAG:Ce,Ca,Mg scintillation fibers was produced by ISMA team! Crystals up to 200 mm in length were successfully grown using the Czochralski method, and 101 scintillation fibers of 50×1×1 mm³ were fabricated for testing in the Spaghetti Calorimeter (SpaCal) prototype in CERN.

In High-Energy Physics, particularly in collider experiments with high luminosity, detectors operate under extremely challenging conditions, including intense radiation and high event rates, that impose stringent demands on the scintillating crystals used in calorimetry. A notable example is the SpaCal, a type of sampling electromagnetic calorimeter consisting of scintillating fibres embedded within a dense absorber.

The planned tests in CERN will check YAG:Ce,Ca,Mg fibers against the key specifications that crystals must meet to ensure reliable operation and optimal performance.

The specifications include:1 MGy, as any radiation-induced deterioration in the crystal

• Tolerance for high radiation doses to 1 MGy, as any radiation-induced deterioration in the crystal properties would lead to a degradation of the detector's energy resolution and overall performance;

• The scintillation decay time is another critical parameter - the pulse should ideally be contained within the bunch crossing window to prevent pile-up effects, where residual light from a previous event could contaminate the signal from the subsequent event, leading to distorted/falsified measurements. In case of HL-LHC, the bunch crossing is 25ns.

• Light yield (LY) is equally important - the material must be sufficiently bright and efficiently convert the deposited energy into photons. Initial specifications suggest a minimum LY above 10,000 photons/MeV. Additionally, the crystal should have good transparency to its own emission wavelength (in between 80 and 90%) to ensure efficient light collection, and its emission spectrum should match the quantum efficiency of the photodetectors used for readout (usually around 400 – 600 nm).

• The crystals should also possess good mechanical properties to withstand the stresses of detector assembly and operation and be non-hygroscopic, and their production process should be reproducible to ensure uniform performance across the many crystal elements typically needed in a calorimeter system.

• Furthermore, inhomogeneities in scintillation decay time and LY along crystal ingots or fibres must be carefully controlled, with simulations indicating that longitudinal variations of LY should be kept below 2% per cm to maintain detector performance. Cost-effectiveness and scalability of production are additional practical considerations for large-scale detector systems.s would lead to a degradation of the detector's energy resolution and overall performance.

Cryst

aTls up to 200 mm in length were succes

sfully grown using the Czochralski m

ethod, and scin

tillation fibers of 50×1×1 mm³ and 100×1×1 mm³ were fabricated for testing in the Spaghetti calorimeter prototype