V. Kononets

Photoinduced refractive index variation within picosecond laser pulses excitation as the indicator of oxyorthosilicates single crystals composition modification

For the first time, the diagnostics of oxyorthosilicates single crystals based on self-action of picosecond range laser pulses at 1,064 nm (1.17 eV) has been performed. High sensitivity of the photoinduced refractive index variation to the substitution of the Lu atoms by Gd in the LSO/LGSO crystalline host as well as to the admixture of Ce was found. The effect can be explained with different electron detrapping-recombination process efficiencies due to the resonant electron excitation from the deep traps in the gap attributed to intrinsic oxygen vacancies.

Test beam results of a high granularity LuAG fibre calorimeter prototype

The progresses in the micropulling-down technique allow heavy scintillating crystals to be grown directly into a fibre geometry of variable shape, length and diameter. Examples of materials that can be grown with this technique are Lutetium Aluminum Garnets (LuAG, Lu3Al5O12) and Yttrium Aluminum Garnets (YAG, Y3Al5O12). Thanks to the flexibility of this approach, combined with the high density and good radiation hardness of the materials, such a technology represents a powerful tool for the development of future calorimeters. As an important proof of concept of the application of crystal fibres in future experiments, a small calorimeter prototype was built and tested on beam. A grooved brass absorber (dimensions 26cm×7cm×16cm) was instrumented with 64 LuAG fibres, 56 of which were doped with Cerium, while the remaining 8 were undoped. Each fibre was readout individually using 8 eightfold Silicon Photomultiplier arrays, thus providing a highly granular description of the shower development inside the module as well as good tracking capabilities. The module was tested at the Fermilab Test Beam Facility using electrons and pions in the 2–16 GeV energy range. The module performance as well as fibre characterization results from this beam test are presented.

Engineering of bulk and fiber-shaped YAGG:Ce scintillator crystals

Composition-property correlations have been systematically studied in the full concentration range of Y3Al5−xGaxO12:Ce (YAGG:Ce) scintillator crystals. The most promising compositions for new high energy physics experiments at colliders have been determined with the light output >200% relative to BGO and fast luminescence decay. Codoping with Ca2+ provides the decrease of phosphorescence intensity to 0.2% after 0.6 μs and shortening of the luminescence decay constant to 21 ns. Factors affecting the scintillation decay time in YAGG:Ce have been discussed. The crystals show weak transmission loss under γ-irradiation. The feasibility to produce YAGG:Ce fibers using the μ-PD method has been shown.

Development of YAG:Ce,Mg and YAGG:Ce Scintillation Fibers

The chapter overviews the status of works on fabrication of long garnet fibers for application in high energy physics experiments. Y3Al5O12:Ce,Mg (YAG:Ce,Mg) and Y3Al5−xGaxO12:Ce (YAGG:Ce) fibers are grown by the µ-PD method. The scintillation and optical parameters of fibers are controlled by optimization of concentration of isovalent (Ga3+) and aliovalent (Mg2+) codoping, as well as by choice of growth parameters.