Cerium-doped Lutetium Oxyorthosilicate Research Articles

Hydrothermal synthesis of Ce: Lu 2SiO 5 scintillator powders

The synthesis of cerium-doped lutetium oxyorthosilicate (LSO) polycrystalline powders was investigated by a hydrothermal process. The precursor was obtained by the hydrothermal reaction of Lu(NO 3) 3 with Na 2SiO 3 at 200 °C for 10 h by using urea as precipitator, followed by a calcination under proper temperatures. The results of XRD indicated that the precursor was crystallized into A-type LSO phase at 1000 °C, and transferred to B-type LSO phase when temperature was raised above 1050 °C. After being heated at 1250 °C for 2 h, single phase of B-type LSO powder was synthesized with homogeneous distribution of particle size ranging from 200 to 300 nm. The photoluminescence spectrum of as-synthesized LSO: Ce powders showed a typical broad emission peak centered at 404 nm, corresponding to the 5d 1–4f transition of Ce 3+.

Scintillation Properties of Praseodymium Doped LuAG Scintillator Compared to Cerium Doped LuAG, LSO and ${\rm LaBr} _{3}$

Properties of praseodymium and cerium doped Lutetium Aluminum Garnet (LuAG) were compared with cerium doped Lutetium Oxyorthosilicate (LSO) and Lanthanum Bromide (LaBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ). Light yield, its non-proportionality relative to 662 keV gamma -rays and the dependence of the energy resolution on energy of the detected gamma -rays were measured. LuAG:Pr turned out to have good proportionality, with deviation from unity around 10% at 16.6 keV and 3% at 59.5 keV. This, together with relatively high light yield of 5600 phe/MeV results in a very good energy resolution of LuAG:Pr of 5.1% measured with 662 keV gamma-rays. The measured time resolution of 308 ps is significantly larger than that of 166 ps obtained for LSO:Ce. This can be explained by smaller light yield of LuAG:Pr and the fact that only about 25% of its scintillation is emitted in short decay time modes of 17.6 ns and 52 ns, while the rest is decaying with long time modes of 1.4 mus and 9 mus.

The Effect of Calcium Co-Doping on Praseodymium Doped LSO

Cerium-doped lutetium oxyorthosilicate (LSO:Ce) is a well-known scintillator whose high density (7.4 g/cc), high light yield ( ~ 6 times that of BGO), and fast decay time ( ~ 43 ns) make it especially well suited for use in Positron Emission Tomography. Recent work suggests that divalent calcium co-doping eliminates many of the shallow electron traps, thus facilitating fast energy transfer to the Ce3+ luminescence centers and shortening the scintillation decay time to ~ 30 ns. Here we report preliminary observations of the effect of Ca2+ co-doping on the crystal growth, photoluminescence, and scintillation properties of LSO:Pr. Single crystals with Pr concentrations ranging from 0.05% to 0.2% and Ca2+ concentrations up to 0.2% were grown via the Czochralski technique. Absorption, emission, and excitation spectra revealed the numerous 5d-4f and 4f-4f transitions characteristic of trivalent Pr. The main optical absorption due to Ca2+ occurs in the far UV, similar to previous observations of LSO:Ce, but with a more intense tail extending through the visible region. Consequently, 4f to 5d optical excitation ( ~ 260 nm) is greatly reduced in Ca co-doped samples, and the related 5d to 4f emission ( ~ 400 nm) is largely absent. Optical excitation ( ~ 450-500 nm) of the red ( ~ 610 nm) emission appears to be unaffected, for the most part, by the presence of Ca2+. The scintillation decay of LSO:Pr is the sum of two exponential components with time constants of 7-8 and 26-29 ns, similar to previous reports. The addition of Ca2+ appears to relatively enhance the shorter component while reducing the longer one, although one or more additional slow components appear.

Emission Spectra of LSO and LYSO Crystals Excited by UV Light, X-Ray and $\gamma$-ray

Because of their high stopping power (Xo = 1.14 cm, RMoliere = 2.07 cm) and fast (~ 40 ns) bright (4 times of BGO) scintillation, cerium doped lutetium oxyorthosilicate (LSO) and cerium doped lutetium-yttrium oxyorthosilicate (LYSO) crystals have attracted a broad interest in the high energy physics community. This paper presents a comparative study on emission spectra measured for large size BGO, lead tungstate (PbWO4), LSO and LYSO samples excited by UV light (photo-luminescence) with and without internal absorption, X-ray (X-luminescence) and gamma-ray (radio-luminescence). A red shift was observed between the emission spectra with internal absorption as compared to that without. An additional red shift and a significant red component were observed in the radio-luminescence spectra measured for LSO samples but not LYSO samples, which were disappeared after a gamma-ray irradiation with an accumulated dose of 5 x 103 rad. This is the only significant difference observed between the large size LSO and LYSO samples. The origin of these red shifts and the consequence to their light output and applications in the high energy and nuclear physics experiments are discussed.

A new approach for pulse processing in positron emission tomography

In this paper, we propose a new technique for positron emission tomography (PET) pulse processing that has the potential to overcome design limitations in PET arising from the need to use fast, high-cost analog-to-digital converters (ADCs). In this technique, we consider the voltage pulse derived from the charge pulse generated by a scintillator/photomultiplier tube (PMT) detector upon a detection event and model the voltage pulse by a fast, linearly rising edge followed by a slower exponential decay. Based on this model, we show that the basic parameters of the voltage pulse that are relevant for PET event detection can be determined from a trigger time and four time intervals measured on the pulse. We also discuss an electronic implementation in which the required measurements can be obtained by using clocks, comparators, and registers, thereby eliminating the use of ADCs and constant fraction discriminators in PET front-end electronics. We conduct computer simulation studies to evaluate the performance of the proposed technique and our results are promising. When used with Cerium Doped Lutetium Oxyorthosilicate (LSO)/PMT, the proposed technique can generate accurate results for the photon energy, the event time, and the decay-time constant. In addition, it can support an energy resolution of about 30% and a coincidence window of about 10 ns. On the other hand, in its present form the proposed technique is not suitable for use with BGO/PMT due to its low light yield.

Growth and characteristics of LYSO (Lu 2(1−x−y)Y 2xSiO 5:Ce y) scintillation crystals

In this experiment, properties of LYSO crystals with different yttrium concentrations were investigated by Czochralski method. The concentrations of yttrium and cerium were analyzed by ICP-AES and the distribution coefficients of yttrium and cerium in LYSO crystal were calculated. It was found that the light output and the decay time of LYSO crystals are almost the same as that of cerium-doped lutetium oxyorthosilicate crystal (LSO). The energy resolutions of LYSO crystals, however, fluctuated in a large range.

A new radiation damage phenomenon of LSO:Ce scintillation crystal

Cerium-doped lutetium oxyorthosilicate (LSO:Ce) is an excellent scintillator with a large radiation hardness. But, in this work, some LSO:Ce crystals grown by SIC showed a new radiation damage phenomenon after exposure to 60Co γ-rays. An absorption band peaking at near 430 nm was observed. Because of the absorption the emission spectra were distorted but no new emission center appeared. There is no new thermoluminescence (TL) peak in the TL curve but the relative intensity of peaks is different from that of normal samples. The peaks at 490 and 546 K may be attributed to the appearance of absorption band that was proved by annealing at different temperatures. Absorption band can be eliminated a little at 200 °C and completely at 300 °C, either in air or in N 2 atmosphere.

Optimization of dual Layer phoswich detector consisting of LSO and LuYAP for small animal PET

Phoswich detectors for small animal PET have been developed to measure the depth of interaction and to improve resolution performances. The aim of this study was to perform simulations to design the optimum lengths of crystals composing a dual layer phoswich detector. A simulation tool, the Geant4 Application for Tomographic Emission (GATE), was used and validated against a commercially available small animal PET using a dual layer phoswich detector. The newly designed small PET system employed cerium doped lutetium oxyorthosilicate (LSO) -cerium doped lutetium-yttrium aluminum perovskite (LuYAP) phoswich detector modules, which consisted of 8/spl times/8 arrays of dual layer crystals, with a 2/spl times/2 mm sensitive area, coupled to a Hamamatsu R7600-00-M64 position sensitive photomultiplier tube (PSPMT). The sensitivities and variations of the radial resolutions were simulated by varying the length of the LSO front layer from 0 to 10 mm, while the total length (LSO+LuYAP) was fixed to 20 mm for 10 and 19 cm diameter ring scanners. The results support the validity of the simulation tool. The radial resolution uniformity was markedly improved using the depth of interaction (DOI) information, and the optimal lengths of the crystal layers for minimizing the variation of the radial resolutions also existed. In the 10 cm ring scanner configuration, the radial resolution was kept below 3.4 mm, over 8 cm field of view (FOV), while the sensitivity was higher than 7.4% for the LSO 5 mm : LuYAP 15 mm phoswich detector. The resolution variations were minimized to less than 3.6 mm, over 16 cm FOV, using a LSO 6 mm : LuYAP 14 mm phoswich detector for the 19 cm ring scanner. In this study, the optimal length of the dual layer phoswich detector was derived to achieve a high and uniform radial resolution.

First in-beam PET imaging with LSO/APD array detectors

The performance and in-beam imaging capabilities of two position-sensitive /spl gamma/-ray detectors consisting of Hamamatsu avalanche photodiode arrays (S8550) individually coupled to crystals of cerium-doped lutetium oxyorthosilicate (LSO) are presented. The two detectors were operated in coincidence at the medical beam line of the Gesellschaft fu/spl uml/r Schwerionenforschung, in Darmstadt, Germany. In a first set of experiments, their imaging performance was tested before, during, and after the irradiation of phantoms of polymethylmethacrylate with carbon ion beams with fluences equivalent to 1000 typical daily therapeutic fractions. Only minor energy, time, and spatial resolution deterioration was observed, with the initial values being recovered after stopping the irradiation. A second set of experiments successfully imaged the depth distribution of positron emitter radionuclides created in a phantom that stopped the high-energy carbon ion beam. The particular details for the in-beam PET acquisition are shortly outlined. The obtained results show that LSO is a suitable material for in-beam PET and that its coupling with avalanche photodiode arrays is feasible for a PET system dedicated to in-beam monitoring of ion therapy.

The temperature effect of Lu2SiO5:Ce3+ luminescence

The excitation and emission spectra of cerium-doped lutetium oxyorthosilicate samples, single crystal and powder microcrystal, were measured at room temperature with a Gaussian multi-peaks fit to distinguish the contributions of emission from two different Ce3+ sites. The temperature dependence of X-ray excited luminescence and the thermoluminescence glow curves from these samples were also investigated in the range of 100–500K. The thermal quenching of the luminescence occurred above 200K for both kinds of samples. According to classical thermal quenching theory, the temperature dependence was fitted with activation energy of 0.192 and 0.203eV for the single crystal and the powder sample, respectively. The deviation of experimental data from the theoretical fit in the temperature dependence of LSO single crystal was correlated to the rich structures in the thermoluminescence glow curves, especially in the high temperature range.

Scintillation characteristics of lutetium oxyorthosilicate (Lu 2SiO 5:Ce) crystals doped with cerium ions

Cerium-doped lutetium oxyorthosilicate crystals with dimension of ∅40×60 mm 3 were grown by Czochralski method from an inductively heated iridium crucible. The crystal structure was examined by XRD and confirmed to be monoclinic symmetry. Its optical transmission, UV-excited, X-ray excited emission and light yield were measured at room temperature. Its decay time was also tested under optical excitation and gamma excitation, respectively.

Optical response of cerium-doped lutetium oxyorthosilicate coatings at shocked surfaces

Shock experiments were performed to characterize the triboluminescent signature of surface coatings of powdered cerium-doped lutetium oxyorthosilicate suspended in a silicate binder. This coating shows prompt, nanosecond timescale light emission when driven by explosive detonation. When properly applied to a surface, it may be used to sense the arrival of a shock, or to image the propagation of a shock front.

New LSO based scintillators

Cerium-doped lutetium oxyorthosilicate (LSO) is amongst the most promising new scintillators discovered in almost five decades, with a unique combination of important properties for X and gamma-ray spectroscopy, namely: high density, fast decay, and large light yield. LSO seems to be a prime candidate to replace BGO in PET systems. However, the practical utilization of LSO is hindered by difficulties related to crystal growth (Czochralski method) due to the high temperatures employed. A new approach has been developed using a low-temperature crystal growth technology to produce scintillating LSO crystals. Light transparent polycrystalline LSO samples of a few mm/sup 3/ in volume were grown and characterized by XRD, optical absorption, light decay measurement and gamma-ray spectral response. The properties of the new crystals compared well with high-quality crystals grown by the Czochralski method.

Electron-lattice coupling parameters and oscillator strengths of cerium-doped lutetium oxyorthosilicate

Optical absorption of single-crystal, cerium-doped lutetium oxyorthosilicate has been carefully measured in the temperature interval 10-300 K. Prominent Gaussian absorption peaks occur at 3.432{+-}0.002 eV (peak a), 3.502{+-}0.002 eV (peak b), 4.236{+-}0.0002 eV (peak c), and 4.746{+-}0.0002 eV (peak d), in excellent agreement with previously reported excitation spectra. The second moments are well described by the usual linear model, yielding the Huang-Rhys parameter (S) and vibrational quantum energies for the individual peaks. All absorption bands are characterized by S>5 indicating strong coupling between the Ce{sup 3+} ion and lattice. Temperature dependence of the band centroids exhibits contrasting behavior that is dominated by higher-order coupling terms in the linear harmonic oscillator model or by crystal-field effects. Oscillator strengths of the 4f{yields}5d transitions are calculated from Smakula's formula and knowledge of the Ce{sup 3+} distribution between the two crystallographically inequivalent sites. Values for peaks b, c, and d range from approximately 0.003 to 0.004, and peak a spans magnitude approximately 0.012 to 0.018. From the known correlation between average Ce{sup 3+}-ion-ligand distance and oscillator strength, we tentatively conclude that peak a is correlated with the seven-oxygen-coordinated site, and peaks b, c, and d are associated with the six-oxygen-coordinated site. These results supportmore » the previously proposed two-activation-center model and identify the centers as the two crystallographically inequivalent substitutional sites. (c) 2000 The American Physical Society.« less

Electron traps and transfer efficiency in cerium-doped lutetium oxyorthosilicate scintillators

The ratio of thermoluminescence and scintillation light outputs of Ce : Lu2SiO5 (LSO) was measured as a function of gamma-ray dose. Together, they account for only a fraction of the predicted electron—hole pairs. Electron traps saturate rapidly, and their concentration is at least two orders of magnitude less than that of cerium.

Nonlinear response in the scintillation yield of Lu/sub 2/SiO/sub 5/:Ce/sup 3+/

The absolute light yield of cerium doped lutetium oxyorthosilicate Lu/sub 2/SiO/sub 5/:Ce/sup 3+/ (LSO:Ce) scintillation crystals is presented. From 60 keV to above 1 MeV the light output increases linearly with the gamma-ray energy and is about 67% of that of NaI(Tl/sup +/). However, a nonlinear response is observed for X-ray energies between 5 and 60 keV. For comparison, we also studied the light yield of a Gd/sub 2/SiO/sub 5/:Ce/sup 3+/ crystal and a CsI:Tl crystal as a function of excitation energy.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Radiation damage of a cerium-doped lutetium oxyorthosilicate single crystal

Degradation in optical transmittance due to irradiation with 60Co γ-rays is less than 1% per cm below 10 6 rad, about 2.5% at 10 7 rad, and 7% at 10 8 rad. Spontaneous recovery occurred only partially with a time constant of the order of days to tens of days. Neither recovery nor damage was sizable upon exposure to UV light. Almost full recovery occurred by thermal annealing at 300°C for one day.

Evaluation of cerium doped lutetium oxyorthosilicate (LSO) scintillation crystals for PET

A new scintillation crystal, cerium-doped lutetium oxyorthosilicate (LSO), was recently discovered, with light intensity 75% of NaI(Tl), scintillation decay time of 12 ns (30%) and 42 ns (70%), effective Z of 66, and density of 7.4 g/cc. The fast decay time and scintillation light output of LSO are superior to those of bismuth germanate (BGO) for positron emission tomography (PET) and the stopping power of LSO for 511 keV photons is only slightly lower than that of BGO. The authors directly compared the detection characteristics relevant to PET applications of small crystals of LSO (2*2*10 mm) with those of BGO. The energy resolution at 511 keV was 12% FWHM for LSO and two to three times wider for BGO. The coincidence timing of two opposing crystals, using a position sensitive photomultiplier tube (PMT) (Hamamatsu R2486), were 1.4 ns FWHM for LSO and more than three times higher for BGO. Using a fast PMT (Hamamatsu R3177), coincidence timing for LSO yielded 0.46 ns FWHM. These crystals are being used to simulate a small-scale PET scanner and to investigate its imaging performance. >

Cerium-doped lutetium oxyorthosilicate: a fast, efficient new scintillator

The authors discuss a single-crystal inorganic scintillator, cerium-doped lutetium oxyorthosilicate (Lu/sub 2(1-x)/Ce/sub 2x/(SiO/sub 4/) or LSO). It has a scintillation emission intensity which is approximately 75% of NaI(Tl) with a decay time of approximately 40 ns. The peak emission wavelength is 420 nm. It has a very high gamma-ray detection efficiency due to its density of 7.4 g/cm/sup 3/ and its effective atomic number of 66. Its radiation length of 1.14 cm is only slightly longer than bismuth germanate (BGO). The scintillation properties of Ce-doped LSO are compared to NaI(Tl), BGO, and cerium-doped gadolinium oxyorthosilicate (GSO). In addition to desirable physical properties such as high density and high atomic number, LSO also processes a combination of high emission intensity and fast decay which together are superior to any other known single crystal scintillator. >