Experimental research on light response of CsI:Tl, that was performed in the last 30 years, have shown that spectrometry parameters of this crystal are influenced by existence of slow scintillation ...components and could be improved by increasing the peaking time. In this study authors analysed and discussed the non-proportionality, number of photoelectrons and energy resolution (with their intrinsic, statistical and noise contributions) as a function of light pulse integration time (adequately to the peaking time known from analogue readouts). The study of light responses of CsI:Tl crystal after interaction with gamma radiation was performed by acquisition of raw single scintillation signals using a photomultiplier and a high class digital oscilloscope. The analysis was performed off-line using Python scripts. The crystal was excited using X-ray and gamma-ray sources with energies from 22 keV up to 835 keV at 293 K (＋20 °C). The data was processed with integration time up to 150μs, which was not achievable so far with analogue electronics commonly used in gamma-ray spectrometry with scintillation detectors. This study considers the problem of the energy resolution as good as other spectrometry parameters improvement using a digital light pulse processing.
Time-resolved luminescence of YAG-Ce (150 ppm) fiber crystal with Mg co-doping was studied under pulsed X-ray excitation and γ-rays (Cs 662 keV). The initial part of decay kinetics under X-ray ...excitation is faster than for direct cerium excitation (63 ns). Decay kinetics is also characterized by the presence of slow components with at least two characteristic times longer than Ce3+ radiation time. The slowest one which dominates for t > 500 ns in YAG-Ce without Mg co-doping practically vanishes for samples with 50 ppm co-doping. Decay kinetics under γ-rays are characterized by slower rise time than that under X-rays. These properties can be explained by competition of energy transfer and energy losses in track regions. The distribution of excitations in tracks produced by X-rays differs from that in tracks produced by γ-rays, since the energy of primary electron after γ-quantum conversion is much higher than after X-ray absorption. The stopping power for energetic electrons decreases with increase of electron energy, and therefore the density distribution after X-ray conversion is shifted to higher densities, Therefore, the acceleration of recombination and quenching of excitations is more prominent under X-ray excitation. Specific role of Ce4+ induced by Mg co-doping is also discussed in the paper.
•Samples YAG-Ce,Mg grown by micro-pulling-down were studied under X-ray and γ-rays.•Luminescence decay becomes faster with increase of Mg concentration.•Slow component vanishes for samples with 50 ppm Mg co-doping.•Decay kinetics under γ-rays show rise part and is slower than under X-rays.•The difference is explained using of the excitation densities distribution in track.
Although light continues to be emitted from insulating crystals used as scintillators over a period of nanoseconds to microseconds after stopping of an energetic particle, much of what determines the ...nonlinearity of response goes on in the first picoseconds. On this time scale, free carriers and excitons are at high density near the track core and thus are subject to nonlinear quenching. The hot (free) electrons eventually cool to low enough energy that trapping on holes, dopants, or defects can commence. In the track environment, spatial distributions of trapped carriers determined on the picosecond time scale can influence the proportionality between light yield and the initial particle energy throughout the whole light pulse. Picosecond spectroscopy of optical absorption induced by a short pulse of above-gap excitation provides a useful window on what occurs during the crucial early evolution of excited populations. The laser excitation can be tuned to excite carriers that are initially very hot (~3 eV) relative to the band edges, or that are almost thermalized (~0.1 eV excess energy) at the outset. Undoped and doped samples of NaI:Tl(0%, 0.1%), CsI:Tl(0%, 0.01%, 0.04%, 0.3%), and SrI sub(2):Eu(0%, 0.2%, 0.5%, 3%) are studied in this work.
Dense interband electronic excitations on the order of 0.2 electron-hole pairs per nm super(3) are encountered in a number of circumstances of fundamental and practical significance. We report ...measurements of the kinetic order and rate constants of nonlinear quenching in pure and doped materials with band gaps in the range from 6 eV down to 1.4 eV. The principal method used can be described as interband Z-scan luminescence yield with subpicosecond pulse excitations. A clear delineation of second-order and third-order quenching kinetics is found between oxide and iodide insulating crystals. This delineation suggests that the hot-electron thermalization rate mediated by LO phonon frequencies governs whether free carriers can pair as excitons within the time period of nonlinear quenching.
Thermally stimulated luminescence (TSL) measurements with spectral resolution on undoped NaI and NaI doped with Tl, In, and Eu are presented and analyzed. Based on the trap parameters extracted, ...carrier release rates are calculated as a function of temperature. The parameters calculated at 300 K by whole peak fitting yield release rates which are about 1–2 orders of magnitude higher than those obtained using the initial rise method. These data can be used to test release-rate predictions of the first ab initio calculations of carrier release and capture rates on dopants in NaI by Prange et al. A kinetic model of rate equations describing energy relaxation in NaI with different activators is used to simulate the TSL experiment and suggest an interpretation of the peaks’ origin(s). We found that thallium can trap either charge carrier, electron or hole, while indium is only a hole trap, and europium induces very shallow electron traps in NaI.
A model of energy relaxation in alkali halide scintillators doped with Tl-like activators is presented. Interaction between thermalized charge carriers, their diffusion, and capture by traps are ...considered. The model of energy relaxation suggested in the work includes essential electron excited states in alkali halides doped with Tl-like activators. Self-trapping of holes occurs in alkali halides at LNT, giving rise to creation of self-trapped excitons (STEs). Thallium-like activator impurity can act both as an electron or a hole trap. Once both of the charge carriers are trapped by the dopant, activator recombination channel comes to action. The model is verified using CsI classical scintillation crystals doped with thallium and indium ions in a range of concentrations from 10–4 to 10–1 mol %. Temperature dependences of the STE and the activator-induced emission yield are measured as a function of the activator concentration under continuous X-ray excitation. A system of rate equations is used to simulate the applicability of the model under different excitation conditions. Evaluation of the parameters of the system is done for a numerical solution. The model of energy relaxation suggested allows to explain energy losses in CsI:A scintillators in a 10–300 K temperature range.
Optical absorption, luminescence spectra, scintillation decay curves, and scintillation light yield were measured in a series of undoped yttrium-aluminum garnet (YAG) crystals of different origins. ...This paper reveals a correlation between luminescent properties and scintillation efficiency of undoped YAG crystals. All the samples were separated into three groups, Type I, Type II, and Type III, based on their optical properties and scintillation efficiency. The intrinsic ultraviolet luminescence band peaking around 300 nm is found in the samples with high scintillation yield (Type I). Luminescence intensity of this band depends on the crystal purity and on the stoichiometry of the garnets. The UV emission may be related to e-h recombination in vicinity of vacancies. The garnets of Type II contain more impurities which quench the 300-nm emission. The samples of Type III do not exhibit any significant radioluminescence. Light yield of the finest undoped YAG samples in the series, Type I, is similar to the yield of Ce-doped YAG. This Type of crystals can potentially be used in scintillation detectors.
The luminescence properties of Ce3+, Pr3+, Nd3+, Sm3+, Eu3+ and Tb3+ doped La(PO3)3 phosphate were studied by vacuum ultra-violet spectroscopy at 10K which gives information on the energies of 4f–5d ...excitation and emission and charge transfer bands of the dopants. All data are consistent with available models and have been used to construct the vacuum referred binding energy scheme for all trivalent and all divalent lanthanides in La(PO3)3 phosphate.
•The luminescence spectroscopy of the trivalent lanthanides in La(PO3)3 is presented.•The energy of the first 4f–5d transition and the charge transfer band is in an agreement with model predictions.•The vacuum referred binding energy scheme for lanthanide ions in La(PO3)3 is constructed.
Radioactive contamination of SrI2(Eu) crystal scintillator Belli, P.; Bernabei, R.; Cerulli, R. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2012, Letnik:
670
Journal Article
Recenzirano
Odprti dostop
A strontium iodide crystal doped by europium (SrI2(Eu)) was produced by using the Stockbarger growth technique. The crystal was subjected to a characterization that includes relative photoelectron ...output and energy resolution for γ quanta. The intrinsic radioactivity of the SrI2(Eu) crystal scintillator was tested both by using it as scintillator at sea level and by ultra-low background HPGe γ spectrometry deep underground. The response of the SrI2(Eu) detector to α particles (α/β ratio and pulse shape) was estimated by analysing the 226Ra internal trace contamination of the crystal. We have measured: α/β=0.55 at Eα=7.7MeV, and no difference in the time decay of the scintillation pulses induced by α particles and γ quanta. The application of the obtained results in the search for the double electron capture and electron capture with positron emission in 84Sr has been investigated at a level of sensitivity: T1/2∼1015–1016yr. The results of these studies demonstrate the potentiality of this material for a variety of scintillation applications, including low-level counting experiments.
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