Search

The characteristics of a Gd 3 Al 2 Ga 3 O12 crystal scintillator doped with cerium and co-doped with magnesium and titanium have been studied, mainly in view of using it for the Phase II upgrade of the LHCb electromagnetic calorimeter . Samples of the scintillator were irradiated with γ (60 Co) to 2 kGy and with 24 GeV protons to 900 kGy. The proton fluence value was ∼ 3 ⋅ 1 0 15 cm − 2 . It was found that γ -irradiation did not produce any change in the optical transmission of the crystals in the spectral range of the scintillation light, whereas a degradation after the proton irradiation was measurable. For the 1 cm thick sample, a loss of transmission of 3.6% was measured at the wavelength of maximum scintillation (520 nm), and the measured induced absorption coefficient at this wavelength was ∼ 3.6 m−1. The formation of radioisotopes in the crystal at proton irradiation has been analysed. The formation of isotopes was also simulated with the help of the FLUKA package. The simulation was found to be in a good agreement with experimental results. The results have been used to estimate the expected intensity of parasitic radio-luminescence at high-luminosity operation in a GAGG/W sampling electromagnetic calorimeter.

Cerium-doped mixed garnet-type single crystals (GdxY1-x)3Al2Ga3O12 with different yttrium content have been fabricated and studied as a prospective scintillating material enabling improvement of scintillation properties by tuning the composition of the matrix-building crystal. The influence of the matrix composition on the emitting Ce ion is studied using linear and time-resolved nonlinear optical absorption and time-resolved photoluminescence spectroscopy. The study of photoluminescence at resonant excitation revealed a composite origin of Ce3+ emission band. This behavior is interpreted by the contribution of Ce3+ ions located in inequivalent positions expected due to the disorder caused in the garnet-type lattice of a mixed crystal by compositional fluctuations. The substitution of gadolinium by yttrium in the lattice results not only in an emission blue shift and in decreased splitting of the lowest doublet 5d state of Ce3+ but also in an increased separation between the lowest doublet level 5d1 and the lowest triplet 5d3 level, as well as in changing the rates of intracenter and extracenter energy relaxation.

This report presents results on the significant improvement of GAGG:Ce based scintillation detector performance with temperature decrease. When temperature of a PMT based detector is lowered to -45oC, its amplitude response at registration of γ-quanta is improved by30%; FHHM was found to be better up to factor of 0.85, whereas scintillation kinetics becomeeven faster in crystals co-doped with magnesium and magnesium and titanium. All this opens an opportunity for a wide application of GAGG scintillation detectors, particularly in a combination with SiPM photo-sensors, which signal-to-noise ratio would also improve with temperaturedecrease.

A calcium molybdate ( $\text{CaMoO}_{4}$ ) crystal scintillator, with molybdenum enriched in $^{100}\text{Mo}$ and calcium depleted in $^{48}\text{Ca}$ ( $^{40}\text{Ca}{}^{100}\text{MoO}_{4}$ ), was developed by the Advanced Molybdenum based Rare process Experiment (AMoRE) collaboration to search for a neutrinoless double beta ( $0\nu \beta \beta $ ) decay of $^{100}\text{Mo}$ . We are planning to use about 10 kg of $^{40}\text{Ca}{}^{100}\text{MoO}_{4}$ crystals as cryogenic bolometers for the first phase of the experiment (AMoRE-I) at the Yang Yang underground laboratory (Y2L) in Korea. This experiment calls for an extremely low level of radioactive contamination in detectors, particularly by thorium, uranium, and radium decay chains. We measured scintillation properties and radioactive contamination of $\text{CaMoO}_{4}$ and $^{40}\text{Ca}{}^{100}\text{MoO}_{4}$ crystals at the Y2L. We also estimated the acceptable level of internal radioactive background using Monte Carlo simulation for the AMoRE-I.

A scintillating crystal that contains a candidate isotope for DBD provides a promising technique for the high detection-efficiency and good energy resolution. The AMoRE (Advanced Molybdenum based Rare process Experiment) collaboration is studying the potential of CaMoO4 scintillation crystals for searches for looMo 0v DBD.

Scintillation properties and radioactive contamination of calcium molybdate scintillating crystals depleted in 48Ca and enriched in 100Mo (40Ca100MoO4 ) have been studied to prepare a 100Mo-based neutrinoless double beta decay experiment. The prospects of a neutrinoless double beta decay experiment using 40Ca100MoO4 crystals are discussed.

In view of the successful use of perovskite-like compounds in technological applications, a study on the segregation of the dopant in the growth from the melt of single crystals of KMgF3 :Ce3+1 is carried out with particular concern to the influence of impurity concentration and pulling rate. The effective segregation coefficient of Ce3+ in KMgF3 is found to have the approximately constant value of 0.22 for solidified fractions lower than 25% and to considerably increase in the rest of the growth process because of matrix evaporation.