Merry Koschan

Effect of codoping on scintillation and optical properties of a Ce-doped Gd3Ga3Al2O12 scintillator

Single crystals of Gd3Ga3Al2O12 : Ce with different codopants were successfully grown using the Czochralski technique. Optical and scintillation properties of these codoped crystals were studied in detail including absorption, photoluminescence excitation and emission, decay time and thermoluminescence. This study revealed that while boron codoping improves the scintillation light output and energy resolution and decreases self-absorption in these crystals, calcium codoping affects their properties in the opposite manner. In addition to antisite defects, the effect of room temperature trap centres on the sensitivity of these crystals to light exposure is also reported for the first time. Light sensitivity was also found to be affected with the incorporation of codopants in the lattice. The effect of annealing in oxidizing and reducing atmospheres on the scintillation and optical properties of differently codoped crystals was also investigated in detail in order to better understand the defect structure of these crystals. All these measurements together are used to explain the effect of codoping on the crystal field and defect structure of these crystals.

The Effect of

Low temperature (~35 K) measurements of the scintillation kinetics of Y2SiO5:Ce (YSO:Ce) have previously illustrated that shallow electron traps can play an important role in the scintillation mechanism. In addition, divalent calcium co-doping of isostructural Lu2SiO5:Ce (LSO:Ce) has been shown to eliminate shallow electron traps and decrease scintillation decay time while maintaining high light output. Here we investigate the effect of Ca2+ codoping on the trap populations and scintillation kinetics of YSO:Ce. Single crystals were grown with Ca2+ concentrations up to 0.5 at% relative to Y. Thermoluminescence measurements indicate a significant reduction in shallow traps, and a marked change in the scintillation kinetics can be seen in the scintillation time profiles as a result of Ca2+ codoping.

{\hbox {Ca}}^{2+}

Experimental studies of LSO:Ce crystals co-doped with various concentrations of Ca are presented. Photoluminescence decay time, excitation and emission spectra, thermal response and X-ray excited luminescence are investigated as a function of Ca concentration. Experimental data show Ca co-doping does not alter the energy level structure of either Ce1 or Ce2, but reduces the relative population of Ce2 to Ce1. Thus, the luminescence from Ce2 is suppressed, which contributes to the fast scintillation decay of Ca co-doped LSO:Ce.

Codoping on Shallow Traps in YSO:Ce Scintillators

A comparative study of five 5 × 5 × 5 mm3 LSO:Ce samples with different co-dopings of calcium, from 0 to 0.4% is reported. All the results are compared to those obtained with selected 10 × 10 × 5 mm3 LSO crystal, tested in previous studies. The influence of Ca co-dopant on scintillator parameters was studied using a Photonis XP20D0 fast timing photomultiplier. The tests included measurements of light output in terms of number of photoelectrons, measurements of time resolution in coincidence experiments with annihilation quanta from a 22Na gamma source, and decay time constant calculations on the basis of timing spectra obtained using the Bollinger-Thomas single photon method. Also energy resolution for 662 keV from 137Cs gamma source is mentioned at the end of the paper. The results showed the significant influence of the Ca co-dopant on the properties of the LSO scintillators. For low Ca concentrations of 0.1%, photoelectron number and energy resolution were improved up to 7800 phe/MeV and 7.3 % respectively. On the other hand the shortest decay time constants were obtained for higher concentrations of 0.3% and 0.4% of Ca giving values equal to about 30 ns. The time resolution improvement was similar for all the samples and calculated values for a single detector were equal to about 140 ps.

Effect of Ca Co-Doping on the Luminescence Centers in LSO:Ce Single Crystals

The temperature dependence of scintillation decay and rise time was measured for GGAG:Ce and Ca-codoped GGAG:Ce crystals in the temperature range of 10 K to 400 K. The decay and rise times were found to increase with decreasing temperature in the case of GGAG:Ce crystals, while Ca codoping modifies the kinetics such that decay and rise times are constant with the change in temperature. In order to obtain a better understanding of the role of trap centers in the temperature dependence of scintillation kinetics, spectrally resolved thermoluminescence (TL) properties were also studied for these crystals.

Timing Resolution and Decay Time of LSO Crystals Co-Doped With Calcium

This paper investigates the effects of boron and calcium co-doping on the measured energy resolution of Gd3Ga3Al2O12:Ce (GGAG: Ce). For this study, three samples of GAGG were grown using the Czochralski method. The first sample was doped with Ce3+ and was used as a reference for comparison. The next two samples were additionally doped with either B3+ or Ca2+. The boron co-doped sample was found to have an overall improved performance when compared to the reference sample. The light output of the GGAG:Ce,B was measured to be 10% greater than the reference sample. In addition, the sample was found to have less charge trapping and a more linear relative light yield response. These factors led to an observed improvement in energy resolution from 9% in the reference sample to 7.8% in the B 3+ co-doped sample. Co-doping with Ca2+ led to an overall reduction in charge trapping; however, the sample suffered a 30% reduction in light output, and it was found to have a less linear relative light yield than the reference sample. Its energy resolution was measured to be 10.1%. The relationship between the measured energy resolution and the other measured properties in these samples is discussed.

Effect of

The detection of ionizing radiation is important in numerous applications related to national security ranging from the detection and identification of fissile materials to the imaging of cargo containers. A key performance criterion is the ability to reliably identify the specific gamma-ray signatures of radioactive elements, and energy resolution approaching 2% at 662 keV is required for this task. In this work, we present discovery and development of new high energy resolution scintillators for gamma-ray detection. The new ternary halide scintillators belong to the following compositional families: AM2X5:Eu, AMX3, and A2MX4:Eu (A = Cs, K; M = Ca, Sr, Ba; X = Br, I) as well as mixed elpasolites Cs2NaREBr3I3:Ce (RE = La, Y). Using thermal analysis, we confirmed their congruent melting and determined crystallization and melting points. Using the Bridgman technique, we grew 6, 12 and 22 mm diameter single crystals and optimized the Eu concentration to obtain the best scintillation performance. Pulse-height spectra under gamma-ray excitation were recorded in order to measure scintillation light output, energy resolution and light output nonproportionality. The KSr2I5:Eu 4% showed the best combination of excellent crystal quality obtained at fast pulling rates and high light output of ~95,000 photons/MeV with energy resolution of 2.4% at 662 keV.

{\rm Ca}^{2+}

In this paper, nine different samples of YAIO3:Ce have been collected and analyzed. The light yield non-proportionality of each sample was measured and used to classify each sample as proportional or non-proportional. A variety of scintillation and optical measurements were conducted on each sample, and the proportional samples were generally found to have a higher light output and better energy resolution. In addition, a strong linear correlation was found between scintillation decay time and the degree of non-proportionality. Based on absorption measurements as well as radioluminescence data, it was determined that the non-proportional samples all shared a range of increased absorption near the cerium 5d absorption edge between about 325 and 400 nm. The increased absorption has been reported in literature, and it is believed to be the result of a material defect introduced during growth. Thermoluminescence glow curves were measured for two representative YAIO3:Ce samples, one from each proportionality grouping, and it was determined that there was an observable change in defect structure, but there were no additional traps visible in the glow curves of either the proportional or non-proportional samples. However, the intensity of the 105 K thermoluminescence peak was found to be approximately a factor of two greater in the non-proportional samples. Since the lifetime of this peak is known to be between 25 and 81 ns, it was determined to be the likely cause of the slower decay in the non-proportional samples.

Co-Doping on the Scintillation Kinetics of Ce Doped

A quaternary iodide KCa0.8Sr0.2I3:Eu2+ scintillator with 2.5% energy resolution at 662 keV in a 5 mm3 sample shows great potential for use in gamma-ray spectroscopy applications. In this work, we report the state-of-the-art growth of high quality 25, 38, and 50 mm diameter KCa0.8Sr0.2I3:Eu2+ single crystals by the vertical self-seeding Bridgman method. KCa0.8Sr0.2I3:Eu2+ with a size of ∅25 mm × 25 mm can achieve excellent energy resolutions of 3.15% at 662 keV and 6.8% at 122 keV irradiation, which are superior to that of a commercial NaI:Tl+ of the same size. The nonuniformity of light collection and production in ∅25 mm × 25 mm and ∅38 mm × 38 mm KCa0.8Sr0.2I3:Eu2+ crystals was evaluated by using a technique based on a collimated 137Cs source and coupling the crystal to a photomultiplier tube (PMT) in different directions. The performances of the packaged crystals for practical use were also measured.

{\rm Gd}_{3}{\rm Ga}_{3}{\rm Al}_{2}{\rm O}_{12}

Single crystals of Gd3Ga3Al2O12:Ce with Ca, B and Ba codopants were successfully grown using the Czochralski technique. The samples of each composition were irradiated to 10 kGy and 100 kGy gamma dose to determine the radiation induced absorption. The Ca co-doped crystal was found to have maximum induced absorption, while B and Ba co-doped were found to be more radiation hard. The reduction in transmission could be partially restored at room temperature without any annealing treatment of the crystals. The additional absorption was also measured after annealing the crystals in reducing environment and compared with the radiation induced absorption. Thermoluminescence measurements were carried out to explain the defect structure and recovery of the transmission reduction at room temperature.