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Purpose: Active matrix flat-panel imagers (AMFPIs) incorporating thick, segmented scintillators have demonstrated order-of-magnitude improvements in detective quantum efficiency (DQE) at radiotherapy energies compared to systems based on conventional phosphor screens. Such improved DQE values facilitate megavoltage cone-beam CT (MV CBCT) imaging at clinically practical doses. However, the MV CBCT performance of such AMFPIs is highly dependent on the design parameters of the scintillators. In this paper, optimization of the design of segmented scintillators was explored using a hybrid modeling technique which encompasses both radiation and optical effects. Methods: Imaging performance in terms of the contrast-to-noise ratio (CNR) and spatial resolution of various hypothetical scintillator designs was examined through a hybrid technique involvingMonte Carlo simulation of radiation transport in combination with simulation of optical gain distributions and optical point spread functions. The optical simulations employed optical parameters extracted from a best fit to measurement results reported in a previous investigation of a 1.13 cm thick, 1016 µm pitch prototype BGO segmented scintillator. All hypothetical designs employed BGO material with a thickness and element-to-element pitch ranging from 0.5 to 6 cm and from 0.508 to 1.524 mm, respectively. In the CNR study, for each design, full tomographic scans of a contrast phantom incorporating various soft-tissue inserts were simulated at a total dose of 4 cGy. Results: Theoretical values for contrast, noise, and CNR were found to be in close agreement with empirical results from the BGO prototype, strongly supporting the validity of the modeling technique. CNR and spatial resolution for the various scintillator designs demonstrate complex behavior as scintillator thickness and element pitch are varied--with a clear trade-off between these two imaging metrics up to a thickness of ~3 cm. Based on these results, an optimization map indicating the regions of design that provide a balance between these metrics was obtained. The map shows that, for a given set of optical parameters, scintillator thickness and pixel pitch can be judiciously chosen to maximize performance without resorting to thicker, more costly scintillators. Conclusions: Modeling radiation and optical effects in thick, segmented scintillators through use of a hybrid technique can provide a practical way to gain insight as to how to optimize the performance of such devices in radiotherapy imaging. Assisted by such modeling, the development of practical designs should greatly facilitate low-dose, soft tissue visualization employing MV CBCT imaging in external beam radiotherapy [ABSTRACT FROM AUTHOR]

The aim of this paper is to study the efficiency of excitonic and activator recombination channels in activated alkali halides depending on the activator concentration. Both theoretical considerations and experimental verification of competition of these channels were carried out. For a model system a CsI-based scintillator was chosen. It is shown that at low temperature (20 K) the excitonic luminescence significantly drops in a hyperbolic law with increase of activator (Tl or In) emission. A corresponding increase of the activator-related recombination channel at 20 K was found to be only 20% of the excitonic yield of pure crystals, reaching a saturation at about 0.04 mol% of the activator. The energy loss observed is attributed to trapping of electron excitations at different centers. This is connected with the competition of electron-hole recombination and trapping of electrons on activators. Estimation of recombination efficiency was done based on the generalized Onsager model. Activator-induced screening, broad spatial distribution of thermalized electrons (mean thermalization length in CsI is about 180 nm) and strongly inhomogeneous electron track structure were taken into account in the model. Energy transfer from the excitons to the activator was suggested to be the main cause of the activator emission observed in doped CsI crystals at 20 K. [ABSTRACT FROM AUTHOR]

SUMMARY This contribution outlines the scenario of the expected atmospheric impairments, which affect a satellite radio link operating in the W band, as derived by the present theoretical and experimental knowledge. The paper discusses the contributions to signal fade due to gases, clouds, scintillation and rain (with emphasis also on the impact of the hydrometeor size distribution), as well as to the depolarization of the electromagnetic waves. The main objective is to assess the constraints to face in the design of a satellite telecommunication system operating in the W band. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Ce-doped Lu3Al5O12 optical ceramics co-doped with Mg2+ are fabricated by solid-state reaction method and further optimized by an air-annealing process. Mg2+ co-doping leads to a significant decrease of thermoluminescence intensity above room temperature and an increase of scintillation light yield (LY) value and fast component content even if the overall scintillation efficiency decreases. Scintillation LY of ∼21900 ph/MeV has been achieved with a short shaping time of 1 μs, and the ratio of LY values for 1 μs and 10 μs shaping times was as high as 79%. The acceleration of scintillation response induced by Mg2+ co-doping and the role of Ce4+ ions in the scintillation mechanism are discussed. [ABSTRACT FROM AUTHOR]

Cerium-doped Gd3( Al, Ga)5 O12 powders have been synthesized with ultrasonic-assisted chemical coprecipitation method ( UACC), and the traditional chemical coprecipitation method ( CC) was also employed for comparison. The structure and morphology of powders were investigated by XRD, BET, and TEM. The powders were used for preparing ceramics at different temperatures. The specific surface areas of UACC and CC powders calcined at 800°C were 66 and 29 m2/g, respectively. Ceramics derived from UACC and CC powders were sintered at 1600°C, and the densities are 6.67 and 6.48 g/cm3, respectively. UACC is an attractive method for synthesizing GAGG powder for preparing ceramic scintillators. [ABSTRACT FROM AUTHOR]

We have developed a hot-pressing method for consolidating garnet scintillator powder of composition Gd3( Al, Ga)5 O12: Ce. Thermodynamic analysis revealed that gallium oxide, which was a constituent of the garnet scintillator powder, would react with the graphite mold beginning at 950°C and would be reduced to gallium metal. To prevent this reaction during hot-pressing, a reaction barrier material was placed between the graphite mold and the scintillator powder. As for the reaction barrier material, 3 Gd AlO3- Al2 O3 powder calcined at 1100°C was found to be suitable because the material provided two important characteristics: the same thermal expansion coefficient as the scintillator material and good sinterability. The Gd3( Al, Ga)5 O12:Ce garnet scintillator powder was hot pressed at 1475°C for 4 h in vacuum, followed by annealing at 1300°C for 4 h in oxygen atmosphere. The thus obtained garnet scintillator successfully satisfied the necessary requirements for use in an X-ray computed tomography detector. [ABSTRACT FROM AUTHOR]

Defects can decrease the efficiency of scintillators by trapping electrons. Here, point defects in REAlO3 and RE3Al5O12 are predicted with pair potential simulations, where RE is yttrium or a trivalent rare earth cation. It was found that REAlO3 shows a preference for Al2O3-excess whereas RE3Al5O12 most readily exhibits RE2O3-excess. Also, lattice volume changes for the energetically favorable intrinsic mechanisms are relatively invariant as a function of RE cation size in RE3Al5O12, but not in REAlO3. However, in non-stoichiometric RE3Al5O12, the energetically preferred disorder mechanism results in an increasing lattice expansion with increasing RE radius whereas, in non-stoichiometric perovskites, a relatively small, radius independent, lattice contraction is predicted. These results illustrate that defect behavior in REAlO3 perovskites and RE3Al5O12 garnets is quite disimilar. [ABSTRACT FROM AUTHOR]

Nonlinear quenching of electron-hole pairs in the denser regions of ionization tracks created by γ-ray and high-energy electrons is a likely cause of the light yield non-proportionality of many inorganic scintillators. Therefore, kinetic Monte Carlo (KMC) simulations were carried out to investigate the scintillation properties of pure and thallium-doped CsI as a function of electron-hole pair density. The availability of recent experimental data on the excitation density dependence of the light yield of CsI following ultraviolet excitation allowed for an improved parameterization of the interactions between self-trapped excitons (STE) in the KMC model via dipole-dipole Förster transfer. The KMC simulations reveal that nonlinear quenching occurs very rapidly (within a few picoseconds) in the early stages of the scintillation process. In addition, the simulations predict that the concentration of thallium activators can affect the extent of nonlinear quenching as it has a direct influence on the STE density through STE dissociation and electron scavenging. This improved model will enable more realistic simulations of the non-proportional γ-ray and electron response of inorganic scintillators. [ABSTRACT FROM AUTHOR]

Optical and luminescence properties were studied in the Ce3+ doped yttrium and lutetium aluminum garnets (YAG, LuAG) admixed by Gd3+ and Ga3+ ions. The single crystalline films were grown by liquid phase epitaxy. Energy transfer from Gd3+ sensitizer to Ce3+ activator ions was established. This energy transfer was observed in a broad range of Gd concentrations which may point to longer range interaction between Gd3+ and Ce3+ ions. [ABSTRACT FROM AUTHOR]

Purpose: Clinical QA in teletherapy as well as the characterization of experimental radiation sources for future medical applications requires effective methods for measuring three-dimensional (3D) dose distributions generated in a water-equivalent medium. Current dosimeters based on ionization chambers, diodes, thermoluminescence detectors, radiochromic films, or polymer gels exhibit various drawbacks: High quality 3D dose determination is either very sophisticated and expensive or requires high amounts of effort and time for the preparation or read out. New detectors based on scintillator blocks in combination with optical tomography are studied, since they have the potential to facilitate the desired cost-effective, transportable, and long-term stable dosimetry system that is able to determine 3D dose distributions with high spatial resolution in a short time. Methods: A portable detector prototype was set up based on a plastic scintillator block and four digital cameras. During irradiation the scintillator emits light, which is detected by the fixed cameras. The light distribution is then reconstructed by optical tomography, using maximum-likelihood expectation maximization. The result of the reconstruction approximates the 3D dose distribution. First performance tests of the prototype using laser light were carried out. Irradiation experiments were performed with ionizing radiation, i.e., bremsstrahlung (6 to 21 MV), electrons (6 to 21 MeV), and protons (68 MeV), provided by clinical and research accelerators. Results: Laser experiments show that the current imaging properties differ from the design specifications: The imaging scale of the optical systems is position dependent, ranging from 0.185 mm/pixel to 0.225 mm/pixel. Nevertheless, the developed dosimetry method is proven to be functional for electron and proton beams. Induced radiation doses of 50 mGy or more made 3D dose reconstructions possible. Taking the imaging properties into account, determined dose profiles are in agreement with reference measurements. An inherent drawback of the scintillator is the nonlinear light output for high stopping-power radiation due to the quenching effect. It impacts the depth dose curves measured with the dosimeter. For single Bragg peak distributions this leads to a peak to plateau ratio of 2.8 instead of 4.5 for the reference ionization chamber measurement. Furthermore, the transmission of the clinical bremsstrahlung beams through the scintillator leads to the saturation of one camera, making dose reconstructions in that case presently not feasible. Conclusions: It is shown that distributions of scintillation light generated by proton or electron beams can be reconstructed by the dosimetry system within minutes. The quenching apparent for proton irradiation, and the yet not precisely determined position dependency of the imaging scale, require further investigation and corrections. Upgrading the prototype with larger or inorganic scintillators would increase the detectable proton and electron energy range. The presented results show that the determination of 3D dose distributions using scintillator blocks and optical tomography is a promising dosimetry method. [ABSTRACT FROM AUTHOR]

Purpose: The authors have developed a trimodal PET/SPECT/CT scanner for small animal imaging. The gamma ray subsystems are based on monolithic crystals coupled to multianode photomultiplier tubes (MA-PMTs), while computed tomography (CT) comprises a commercially available microfocus x-ray tube and a CsI scintillator 2D pixelated flat panel x-ray detector. In this study the authors will report on the design and performance evaluation of the multimodal system. Methods: X-ray transmission measurements are performed based on cone-beam geometry. Individual projections were acquired by rotating the x-ray tube and the 2D flat panel detector, thus making possible a transaxial field of view (FOV) of roughly 80 mm in diameter and an axial FOV of 65 mm for the CT system. The single photon emission computed tomography (SPECT) component has a dual head detector geometry mounted on a rotating gantry. The distance between the SPECT module detectors can be varied in order to optimize specific user requirements, including variable FOV. The positron emission tomography (PET) system is made up of eight compact modules forming an octagon with an axial FOV of 40 mm and a transaxial FOV of 80 mm in diameter. The main CT image quality parameters (spatial resolution and uniformity) have been determined. In the case of the SPECT, the tomographic spatial resolution and system sensitivity have been evaluated with a 99mTc solution using single-pinhole and multi-pinhole collimators. PET and SPECT images were reconstructed using three-dimensional (3D) maximum likelihood and ordered subset expectation maximization (MLEM and OSEM) algorithms developed by the authors, whereas the CT images were obtained using a 3D based FBP algorithm. Results: CT spatial resolution was 85 μm while a uniformity of 2.7% was obtained for a water filled phantom at 45 kV. The SPECT spatial resolution was better than 0.8 mm measured with a Derenzo-like phantom for a FOV of 20 mm using a 1-mm pinhole aperture collimator. The full width at half-maximum PET radial spatial resolution at the center of the field of view was 1.55 mm. The SPECT system sensitivity for a FOV of 20 mm and 15% energy window was 700 cps/MBq (7.8 × 10-2%) using a multi-pinhole equipped with five apertures 1 mm in diameter, whereas the PET absolute sensitivity was 2% for a 350-650 keV energy window and a 5 ns timing window. Several animal images are also presented. Conclusions: The new small animal PET/SPECT/CT proposed here exhibits high performance, producing high-quality images suitable for studies with small animals. Monolithic design for PET and SPECT scintillator crystals reduces cost and complexity without significant performance degradation. [ABSTRACT FROM AUTHOR]

We determine the thermal ionization energy of the excited state of Ce3+ in a SrHfO3 host by a contactless optical method based on the measurement and analysis of delayed recombination decay following UV excitation. We show the applicability of the method for microcrystalline powder samples. The method provides a consistent value of thermal ionization energy of about 0.25 eV, as previously determined by a ther- mally stimulated luminescence (TSL) study after UV illumination. We reveal a low temperature contribution to the delayed recombination signal and address its origin. This contribution indicates a complex interaction of the luminescence center with the host lattice neighborhood and the presence of temperature independent losses of fast scintillation light. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

In the family of application-important complex, oxide single crystal scintillators based on tungstates, aluminum perovskites, and yttrium (lutetium) orthosilicates, selected results of electron spin resonance study are presented. They are focused on various point defects, which participate in the processes of charge carriers transfer and capture. Particular attention is paid to the most natural defects inevitably present in oxide materials such as anion and cation vacancies, antisite defects, self-trapped electron, and hole states. Current understanding of the nature of such charge trapping states and mechanisms of their creation in the selected oxide scintillation materials are discussed as well. [ABSTRACT FROM AUTHOR]

Purpose: Recently, photomultiplier tubes (PMTs) and position sensitive PMTs (PSPMTs) with higher quantum efficiencies (HQE) have been developed. However, it remains unclear whether they actually improve such performances as the energy and spatial resolution for PET and SPECT detectors. Methods: The authors evaluated the quantum efficiencies (QEs) for PMTs and PSPMTs and measured the energy resolution of a 3-in. round HQE PMT combined with various scintillators and compared the results with a conventional normal quantum efficiency (NQE) PMT of the same type. The authors also measured the position and energy performance of a 2-in. square HQE PSPMT combined with scintillator blocks and compared them with a NQE PSPMT of the same size. Results: The energy resolution of the 3-in. round HQE PMT showed higher energy resolution than the NQE with all scintillators. The improvement of the energy resolution was smaller, for all measurements, than the expected value from the quantum efficiency of the PMT but was higher for the scintillators with smaller light outputs. The energy and position performance of the HQE PSPMT based block detectors showed higher position and energy performance than those with NQE. Conclusions: From these results, the authors conclude that both HQE PMT and PSPMT contribute to improve the energy and position performance for PET and SPECT detectors. Significant performance improvements will be expected in PET and SPECT systems by the use of the HQE PMTs or PSPMTs. [ABSTRACT FROM AUTHOR]

Cuprous iodide (CuI) is the ultrafastest inorganic scintillation crystal at present. But the low intensity of its ultrafast component luminescence limits the wide application of CuI at room temperature. In this paper, the photoluminescence (PL) characteristics of different quality CuI crystals before and after annealing in various conditions have been investigated in terms of peak position and peak intensity. The origin of different emission band peaked around 426 nm, 680 nm, 718 nm and 820 nm is discussed and the excitation spectra of two mainly emission bands is obtained. Meanwhile, the relative peak intensity of the ultrafast luminescence component to slow lumiescence component of CuI crystals has been studied with respect to the defect concentration of I vacancies. Especially, the method of improving the intensity of ultrafast compentent luminescence of CuI crystals is concluded. These results can provide an important reference for optimizing the luminescence performance of CuI crystals. [ABSTRACT FROM AUTHOR]

X-ray-excited optical luminescence (XEOL) emission and excitation spectra as well as the EXAFS signal of CdWO4 were measured in the energy region of the Cd and W absorption edges. From EXAFS refinement, structural parameters such as number of atoms, distance from the absorbing atom and width of coordination shells in the W neighborhood were determined. The role of W-O interactions on the intrinsic luminescence of CdWO4 is discussed. The efficiencies of conversion, transfer and emission processes involved in the scintillation mechanism showed to be high when self-trapped excitons are formed locally by direct excitation of W ions. Annihilation of these excitons provides the characteristic scintillation of CdWO4, a broad band emission with maximum at 500 nm. The presence of two energetically different O positions in the lattice gives rise to the composite structure of the luminescence band, and no influence of extrinsic defects was noticed. A mismatch between the X-ray absorption coefficient and the zero-order luminescence curves corroborates that the direct excitation of Cd ions induces secondary electronic excitations not very effective in transferring energy to the luminescent group, WO6. [ABSTRACT FROM AUTHOR]

This study involves the upgrade of a high-resolution position-sensitive detector (HR-PSD) installed on the small-angle neutron scattering spectrometer (SANS-U) at the Japan Atomic Energy Agency. By using both neutron lenses and the HR-PSD, the accessible low- Q limit can be extended to the order of 10−4 Å−1 [ Q is the magnitude of the scattering vector defined by Q = (4π/λ)sinθ, where λ and 2θ are the wavelength and the scattering angle, respectively]. The HR-PSD consists of a cross-wired position-sensitive photomultiplier tube (PSPMT) and a commercial ZnS/6LiF scintillator. To improve the experimental efficiency of focusing small-angle neutron scattering (FSANS) experiments, a high-performance ZnS/6LiF scintillator developed at the Japan Atomic Energy Agency has been utilized. For the PSPMT and data-acquisition system installed on SANS-U, the thickness of the ZnS/6LiF scintillator was optimized by measuring the thickness dependence of the pulse-height spectra. Under the experimental conditions of SANS-U, the optimum thickness of the ZnS/6LiF scintillator (ZnS:6LiF = 2:1) was determined to be 0.433 mm by measuring the total counts and peak positions of the pulse-height spectra. Installation of the optimized ZnS/6LiF scintillator improved detection efficiency by 1.39 times over that of a commercial scintillator at the same level of background counts and Q resolution in FSANS experiments. [ABSTRACT FROM AUTHOR]

SrI2:Eu crystals with 1.5 inch diameter were grown by the vertical Bridgman method. The melting point of SrI2 doped with 5 at % Eu grown feedstock was determined to be 526 °C by differential scanning calorimetry (DSC). XRD proved Pbca structure of SrI2 when the SrI2:Eu sample was packaged with polyethylene film in air. The luminescent properties of SrI2:Eu crystals are presented. Under the excitation of UV light or X-ray, the crystals exhibit a single luminescent peak centered at 435 nm. The decay time of SrI2:5%Eu crystal excited by UV were fitted to be 1.9 μs. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Purpose: In recent times, there has been great interest in the use of Geiger-mode avalanche photodiodes (GAPDs) as scintillator readout in positron emission tomography (PET) detectors because of their advantages, such as high gain, compact size, low power consumption, and magnetic field insensitivity. The purpose of this study was to develop a novel PET system based on GAPD arrays for brain imaging. Methods: The PET consisted of 72 detector modules arranged in a ring of 330 mm diameter. Each PET module was composed of a 4 × 4 matrix of 3 × 3 × 20 mm3 cerium-doped lutetium yttrium orthosilicate (LYSO) crystals coupled with a 4 × 4 array three-side tileable GAPD. The signals from each PET module were fed into preamplifiers using a 3 m long flat cable and then sent to a position decoder circuit (PDC), which output a digital address and an analog pulse of the interacted channel among 64 preamplifier signals tranmitted from four PET detector modules. The PDC outputs were fed into field programmable gate array (FPGA)-embedded data acquisition (DAQ) boards. The analog signal was then digitized, and arrival time and energy of the signal were calculated and stored. Results: The energy and coincidence timing resolutions measured for 511 keV gamma rays were 18.4 ± 3.1% and 2.6 ns, respectively. The transaxial spatial resolution and sensitivity in the center of field of view (FOV) were 3.1 mm and 0.32% cps/Bq, respectively. The rods down to a diameter of 2.5 mm were resolved in a hot-rod phantom image, and activity distribution patterns between the white and gray matters in the Hoffman brain phantom were well imaged. Conclusions: Experimental results indicate that a PET system can be developed using GAPD arrays and the GAPD-based PET system can provide high-quality PET imaging. [ABSTRACT FROM AUTHOR]

Summary An examination of the backscattered electron imaging status in environmental scanning electron microscopy is presented with particular attention to the testing and use of cerium doped yttrium aluminium garnet and yttrium aluminium perovskite scintillation detectors. A comparison is made with plastic scintillating backscattered electron detectors used previously (Nuclear Enterprises type NE102A scintillator). Semi-disk, strip and wedge shapes of these materials have been tested in conjunction with various light-guide geometries. These systems have been combined with two different types of photomultipliers, which also play a critical role in the total detector efficiency. The advantage of increased light output from the monocrystal materials is gained only if matched with suitable light-guides and photomultipliers. The associated problems are discussed and proposals for further work are made for the construction of most efficient backscattered electron detectors in the environmental scanning electron microscope. [ABSTRACT FROM AUTHOR]

Purpose: In small animal imaging using a single photon emitting radionuclide, a high resolution gamma camera is required. Recently, position sensitive photomultiplier tubes (PSPMTs) with high quantum efficiency have been developed. By combining these with nonhygroscopic scintillators with a relatively low light output, a high resolution gamma camera can become useful for low energy gamma photons. Therefore, the authors developed a gamma camera by combining a pixelated Ce-doped Gd2SiO5 (GSO) block with a high quantum efficiency PSPMT. Methods: GSO was selected for the scintillator, because it is not hygroscopic and does not contain any natural radioactivity. An array of 1.9 mm × 1.9 mm × 7 mm individual GSO crystal elements was constructed. These GSOs were combined with a 0.1-mm thick reflector to form a 22 × 22 matrix and optically coupled to a high quantum efficiency PSPMT (H8500C-100 MOD8). The GSO gamma camera was encased in a tungsten gamma-ray shield with tungsten pixelated parallel hole collimator, and the basic performance was measured for Co-57 gamma photons (122 keV). Results: In a two-dimensional position histogram, all pixels were clearly resolved. The energy resolution was ∼15% FWHM. With the 20-mm thick tungsten pixelated collimator, the spatial resolution was 4.4-mm FWHM 40 mm from the collimator surface, and the sensitivity was ∼0.05%. Phantom and small animal images were successfully obtained with our developed gamma camera. Conclusions: These results confirmed that the developed pixelated GSO gamma camera has potential as an effective instrument for low energy gamma photon imaging. [ABSTRACT FROM AUTHOR]

Purpose: Positron emission tomography (PET) detectors that use a dual-ended-scintillator readout to measure depth-of-interaction (DOI) must have an accurate DOI function to provide the relationship between DOI and signal ratios to be used for detector calibration and recalibration. In a previous study, the authors used a novel and simple method to accurately and quickly measure DOI function by irradiating the detector with an external uniform flood source; however, as a practical concern, implementing external uniform flood sources in an assembled PET system is technically challenging and expensive. In the current study, therefore, the authors investigated whether the same method could be used to acquire DOI function from scintillator-generated (i.e., internal) radiation. The authors also developed a method for calibrating the energy scale necessary to select the events within the desired energy window. Methods: The authors measured the DOI function of a PET detector with lutetium yttrium orthosilicate (LYSO) scintillators. Radiation events originating from the scintillators' internal Lu-176 beta decay were used to measure DOI functions which were then compared with those measured from both an external uniform flood source and an electronically collimated external point source. The authors conducted these studies with several scintillators of differing geometries (1.5 × 1.5 and 2.0 × 2.0 mm2 cross-section area and 20, 30, and 40 mm length) and various surface finishes (mirror-finishing, saw-cut rough, and other finishes in between), and in a prototype array. Results: All measured results using internal and external radiation sources showed excellent agreement in DOI function measurement. The mean difference among DOI values for all scintillators measured from internal and external radiation sources was less than 1.0 mm for different scintillator geometries and various surface finishes. Conclusions: The internal radioactivity of LYSO scintillators can be used to accurately measure DOI function in PET detectors, regardless of scintillator geometry or surface finish. Because an external radiation source is not needed, this method of DOI function measurement can be practically applied to individual PET detectors as well as assembled systems. [ABSTRACT FROM AUTHOR]

Calcium molybdate is considered as a very promising scintillator material for experimental studies of rare processes. This paper reports on the production and characterization of a 40Ca100MoO4 scintillator. Using the Czochralski technique, a crystal of high optical quality with total mass 0.55 kg, 42 mm diameter (minimum) and 53 mm 1ength of the cylindrical section was produced from isotopically enriched raw materials, containing 96.1% of 100Mo and 99.964% of 40Ca. To satisfy the requirement of low intrinsic radioactivity the purity of the materials was monitored at different stages of the production process and it is shown that the concentration of 238U and 232Th in the final crystal does not exceed 0.05 ppb. The scintillation properties of 40Ca100MoO4 were measured over the 8 - 300 K temperature range and it is found that the light yield of the 40Ca100MoO4 crystal is very similar to that of the CaMoO4 reference scintillator. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Purpose: To quantify the improvement in megavoltage cone beam computed tomography (MVCBCT) image quality enabled by the combination of a 4.2 MV imaging beam line (IBL) with a carbon electron target and a detector system equipped with a novel sintered pixelated array (SPA) of translucent Gd2O2S ceramic scintillator. Clinical MVCBCT images are traditionally acquired with the same 6 MV treatment beam line (TBL) that is used for cancer treatment, a standard amorphous Si (a-Si) flat panel imager, and the Kodak Lanex Fast-B (LFB) scintillator. The IBL produces a greater fluence of keV-range photons than the TBL, to which the detector response is more optimal, and the SPA is a more efficient scintillator than the LFB. Methods: A prototype IBL + SPA system was installed on a Siemens Oncor linear accelerator equipped with the MVisionTM image guided radiation therapy (IGRT) system. A SPA strip consisting of four neighboring tiles and measuring 40 cm by 10.96 cm in the crossplane and inplane directions, respectively, was installed in the flat panel imager. Head- and pelvis-sized phantom images were acquired at doses ranging from 3 to 60 cGy with three MVCBCT configurations: TBL + LFB, IBL + LFB, and IBL + SPA. Phantom image quality at each dose was quantified using the contrast-to-noise ratio (CNR) and modulation transfer function (MTF) metrics. Head and neck, thoracic, and pelvic (prostate) cancer patients were imaged with the three imaging system configurations at multiple doses ranging from 3 to 15 cGy. The systems were assessed qualitatively from the patient image data. Results: For head and neck and pelvis-sized phantom images, imaging doses of 3 cGy or greater, and relative electron densities of 1.09 and 1.48, the CNR average improvement factors for imaging system change of TBL + LFB to IBL + LFB, IBL + LFB to IBL + SPA, and TBL + LFB to IBL + SPA were 1.63 (p < 10- 8), 1.64 (p < 10- 13), 2.66 (p < 10- 9), respectively. For all imaging doses, soft tissue contrast was more easily differentiated on IBL + SPA head and neck and pelvic images than TBL + LFB and IBL + LFB. IBL + SPA thoracic images were comparable to IBL + LFB images, but less noisy than TBL + LFB images at all imaging doses considered. The mean MTFs over all imaging doses were comparable, at within 3%, for all imaging system configurations for both the head- and pelvis-sized phantoms. Conclusions: Since CNR scales with the square root of imaging dose, changing from TBL + LFB to IBL + LFB and IBL + LFB to IBL + SPA reduces the imaging dose required to obtain a given CNR by factors of 0.38 and 0.37, respectively. MTFs were comparable between imaging system configurations. IBL + SPA patient image quality was always better than that of the TBL + LFB system and as good as or better than that of the IBL + LFB system, for a given dose. [ABSTRACT FROM AUTHOR]

Pr-doped Lu3Al5O12 ( LuAG) transparent ceramic, a potential scintillator material, was fabricated by sinter/hot isostatic pressing ( HIP). The specimens were subjected to various post-densification heat treatments and the evolution of porosity and its relationship to transparency was monitored and studied. Annealing was necessary to remove discoloration and to restore stoichiometry, but when performed at too high a temperature it caused a severe decrease in transparency. Transparency was restored by re HIPing, indicating that some nanometer-size pores remained even after the original HIP cycle, which expanded in size during annealing and contracted again during re- HIPing. Annealing at a lower temperature restored stoichiometry without serious transparency degradation, due to a favorable difference in diffusion rates for mass transfer and O2 − diffusion. This phenomenon illustrates a fundamental difference between residual porosity in ceramics consolidated by pressureless and pressure-assisted processes. [ABSTRACT FROM AUTHOR]

Pr-doped Lu3Al5O12 ( LuAG) transparent ceramic, a potential scintillator material, was fabricated by sinter/hot isostatic pressing ( HIP). The specimens were subjected to various post-densification heat treatments and the evolution of porosity and its relationship to transparency was monitored and studied. Annealing was necessary to remove discoloration and to restore stoichiometry, but when performed at too high a temperature it caused a severe decrease in transparency. Transparency was restored by re HIPing, indicating that some nanometer-size pores remained even after the original HIP cycle, which expanded in size during annealing and contracted again during re- HIPing. Annealing at a lower temperature restored stoichiometry without serious transparency degradation, due to a favorable difference in diffusion rates for mass transfer and O2 − diffusion. This phenomenon illustrates a fundamental difference between residual porosity in ceramics consolidated by pressureless and pressure-assisted processes. [ABSTRACT FROM AUTHOR]

Geometry optimizations of monomers were carried out with the use of Becke's three-parameter hybrid method with Lee, Yang, and Parr (B3LYP) gradient-corrected correlation functional and the standard 6-31G(d) basis set. UV-vis spectra of different naphthalene-POPOP complexes using ZINDO/S method were calculated. In these complexes, poly(methyl methacrylate) effect on chromophores was neglected and chromophores were staked. Analyzing available experimental data and obtained theoretical results, the most probable complex structure is determined. Molecular model of POPOP and naphthalene dimer corresponds to this structure. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

The article presents a study which measures the decay time and weak afterglow of scintillation from YAG:Ce3+ using a high-speed complementary metal oxide semiconductors (CMOS) camera and pulsed X-rays. It also examines the positional variance of the X-ray beam in isolated bunches. It states that the possibility of an X-ray diffraction study at high time and space resolution is shown in the results.

The article discusses a study of the structure of process-induced dislocation loops in silicons using three-dimensional X-ray diffraction imaging (3D-XRDI). The authors annealed the silicon samples using a Jiplelec JetFirst 200C thermal anneal system to begin the formation of dislocation loops (DL) around the indents. They recorded a series of X-ray topographs of both the indents and the DL using a charge-coupled device combined with a high-resolution scintillator crystal. The advantages of the 3D-XRDI technique are also discussed.

Purpose: The purpose of this study was to characterize relative magnitudes of peripheral dose modulations present in helical MDCT resulting from variation in x-ray tube starting position and phantom position relative to isocenter using a novel methodology that employs direct dosimetric measurements and knowledge of scan geometry. The magnitudes of potential dose savings to specific radiosensitive tissues related to the phase of the quasiperiodic dose distribution are also quantified and compared to similar Monte Carlo based studies. Methods: For this study, a Siemens SOMATOM Sensation 16 helical MDCT scanner and a tomographic adult anthropomorphic phantom from the University of Florida phantom series were used for all scans. In addition, a plastic scintillator-based fiber-optic-coupled dosimetry system was used to record real-time axial dosimetric measurements. These direct measurements were used to derive cumulative point doses and tissue doses for helical MDCT using different pitch values and surface to isocenter distances. Results: Cumulative point doses and doses for the lens of the eye and thyroid showed strong variation with both the phase of the dose distribution and phantom positioning relative to isocenter. Depending on the phantom positioning relative to isocenter, individual in-phantom cumulative point dose values were shown to vary anywhere from 0 to 25% lower than the maximum value for scans of pitch 1, and greater than 60% for scans of pitch 1.5. Reduction in total tissue dose to the lens of the eye (thyroid) varied from 0 to 20% (4%) lower than the maximum value for pitch 1, and from 59 (14%) to 71% (19%) lower than the maximum value for scans using pitch 1.5. These values are similar to those found in previous Monte Carlo based studies. The reduction in average total tissue dose between the extremes (±3 cm from nominal) of phantom positioning relative to isocenter for the eye (thyroid) was 16% (13%) for pitch 1, and 14% (12%) for pitch 1.5. Conclusions: As recent Monte Carlo simulations have shown, there exists an inherent uncertainty when performing dose measurements within a phantom during helical MDCT scans. The periodic dose distributions in helical MDCT means that low resolution sampling of local phantom doses could result in dose measurement aliasing. For reliable results, these considerations should be accounted for in helical MDCT phantom dosimetry studies. The variability in surface dose has a strong dependence on phantom positioning relative to isocenter. Dose to tissues such as the lens of the eye and thyroid can be minimized by positioning patients, so these tissues are closer to isocenter because the decrease in x-ray intensity due to beam divergence dominates the increases resulting from increased primary beam exposure overlap. Of course, this dose decrease would have to be balanced against any diminished image quality resulting from misalignment of the patient with the bowtie filter. Additionally, significantly reduced dose to small radiosensitive tissues such as the lens of the eye could occur if it were possible to shift the phase of the periodic dose distribution present in helical MDCT. These dose reductions would come at no cost to image quality. [ABSTRACT FROM AUTHOR]

Purpose: The goal of the present work was to evaluate the accuracy of a plastic scintillation detector (PSD) system to perform in-phantom dosimetry during 192Ir high dose rate (HDR) brachytherapy treatments. Methods: A PSD system capable of stem effect removal was built. A red-green-blue photodiode connected to a dual-channel electrometer was used to detect the scintillation light emitted from a green scintillation component and transmitted along a plastic optical fiber. A clinically relevant prostate treatment plan was built using the HDR brachytherapy treatment planning system. An in-house fabricated template was used for accurate positioning of the catheters, and treatment delivery was performed in a water phantom. Eleven catheters were inserted and used for dose delivery from 192Ir radioactive source, while two others were used to mimic dosimetry at the rectum wall and in the urethra using a PSD. The measured dose and dose rate data were compared to the expected values from the planning system. The importance of removing stem effects from in vivo dosimetry using a PSD during 192Ir HDR brachytherapy treatments was assessed. Applications for dwell position error detection and temporal verification of the treatment delivery were also investigated. Results: In-phantom dosimetry measurements of the treatment plan led to a ratio to the expected dose of 1.003 ± 0.004 with the PSD at different positions in the urethra and 1.043 ± 0.003 with the PSD inserted in the rectum. Verification for the urethra of dose delivered within each catheter and at specific dwell positions led to average measured to expected ratios of 1.015 ± 0.019 and 1.014 ± 0.020, respectively. These values at the rectum wall were 1.059 ± 0.045 within each catheter and 1.025 ± 0.028 for specific dwell positions. The ability to detect positioning errors of the source depended of the tolerance on the difference to the expected value. A 5-mm displacement of the source was detected by the PSD system from 78% to 100% of the time depending on the acceptable range value. The implementation of a stem effect removal technique was shown to be necessary, particularly when calculating doses at specific dwell positions, and allowed decreasing the number of false-error detections-the detection of an error when it should not be the case-from 19 to 1 for a 5% threshold out of 43 measurements. The use of the PSD system to perform temporal verification of elapsed time by the source in each catheter-generally on the order of minutes-was shown to be in agreement within a couple of seconds with the treatment plan. Conclusions: We showed that the PSD system used in this study, which was capable of stem effect removal, can perform accurate dosimetry during 192Ir HDR brachytherapy treatment in a water phantom. The system presented here shows some clear advantages over previously proposed dosimetry systems for HDR brachytherapy, and it has the potential for various online verifications of treatment delivery quality. [ABSTRACT FROM AUTHOR]

Purpose: Three dimensional dose polymer gel dosimetry measurements provide unique information on sophisticated dose distributions. In this study, the authors propose a novel method to improve the accuracy of polymer gel dosimeters by inserting a plastic scintillation detector (PSD) to provide a dose reference. Methods: PSD dosimeters were calibrated using chromatic deconvolution and then inserted into polyacrylanide gel (PAG) dosimeters. The gel and the PSDs were immersed into water and irradiated with 6 MV wedge filtered beams to obtain a wide range of dose variation. Calibration vials containing the same gel were also irradiated to generate a standard calibration curve. The distribution of magnetic nuclear transverse relaxation rate (R2) values of the gel was determined with a multislice multiecho MRI sequence at 1.5 T. Another calibration curve was obtained by assigning the R2 values in the gel surrounding the scintillators to the dose determined by the PSDs. A reference calibration point from a PSD located in a low dose gradient area served to correct the standard calibration method yielding three novel calibration methods. The results were compared with EBT2 GAFCHROMIC™ film measurements acquired in the same condition and with the Pinnacle3 treatment planning dose calculations. Results: The mean absolute error of the standard calibration method ranged from 6.1 to 12.4%. The corresponding gamma index (3%/3 mm distance to agreement) criterion was satisfied for only 56% of the pixels in the middle slice of the gel compared to Pinnacle3 dose calculations and to EBT2 film measurements in the center part of the field. Calibration methods using a PSD reduced the mean absolute error to less than 4%; this value was under 2.6% for one of the three methods. In that case, 98% of the pixels satisfied the gamma index criterion. Conclusions: The accuracy of PAG dosimeters may be highly improved using one reference dose point measurement using a plastic scintillation detector. The best calibration procedure corrected the slope of the calibration curve derived from the calibration vials to match the R2 value around a PSD calibration, while keeping the R2 value at 0 Gy constant. [ABSTRACT FROM AUTHOR]

The article presents research which examined the important aspects of the Cylindrical CCD Laue Octagonal Photo Scintillator (CYCLOPS) multiple diffractometer. The researchers described the patterns in the diffractometer when subtended horizontally by 270 degrees and vertically by 92 degrees. They also assessed different experiments on the potential applications of the Laue neutron diffraction method.

Purpose: Beam-shaping or 'bow tie' (BT) filters are used to spatially modulate the x-ray beam in a CT scanner, but the conventional method of step-and-shoot measurement to characterize a beam's profile is tedious and time-consuming. The theory for characterization of bow tie relative attenuation (COBRA) method, which relies on a real-time dosimeter to address the issues of conventional measurement techniques, was previously demonstrated using computer simulations. In this study, the feasibility of the COBRA theory is further validated experimentally through the employment of a prototype real-time radiation meter and a known BT filter. Methods: The COBRA method consisted of four basic steps: (1) The probe was placed at the edge of a scanner's field of view; (2) a real-time signal train was collected as the scanner's gantry rotated with the x-ray beam on; (3) the signal train, without a BT filter, was modeled using peak values measured in the signal train of step 2; and (4) the relative attenuation of the BT filter was estimated from filtered and unfiltered data sets. The prototype probe was first verified to have an isotropic and linear response to incident x-rays. The COBRA method was then tested on a dedicated breast CT scanner with a custom-designed BT filter and compared to the conventional step-and-shoot characterization of the BT filter. Using basis decomposition of dual energy signal data, the thickness of the filter was estimated and compared to the BT filter's manufacturing specifications. The COBRA method was also demonstrated with a clinical whole body CT scanner using the body BT filter. The relative attenuation was calculated at four discrete x-ray tube potentials and used to estimate the thickness of the BT filter. Results: The prototype probe was found to have a linear and isotropic response to x-rays. The relative attenuation produced from the COBRA method fell within the error of the relative attenuation measured with the step-and-shoot method. The BT filter thickness estimates resulting from the dual energy scans on the breast CT system were equivalent to the manufacturing specifications. The clinical CT evaluation produced data conceptually similar to previous computer simulations and plausible relative attenuation profiles were observed. Conclusions: The COBRA method is a fast and accurate method for BT filter characterization, which requires a simple experimental setup in a clinical environment. Because of the ease of data acquisition, multienergy scans can be acquired which allow characterization of the BT filter thickness. [ABSTRACT FROM AUTHOR]

Purpose: The authors assembled a prototype compact gamma-ray imaging probe (MediPROBE) for sentinel lymph node (SLN) localization. This probe is based on a semiconductor pixel detector. Its basic performance was assessed in the laboratory and clinically in comparison with a conventional gamma camera. Methods: The room-temperature CdTe pixel detector (1 mm thick) has 256×256 square pixels arranged with a 55 μm pitch (sensitive area 14.08×14.08 mm2), coupled pixel-by-pixel via bump-bonding to the Medipix2 photon-counting readout CMOS integrated circuit. The imaging probe is equipped with a set of three interchangeable knife-edge pinhole collimators (0.94, 1.2, or 2.1 mm effective diameter at 140 keV) and its focal distance can be regulated in order to set a given field of view (FOV). A typical FOV of 70 mm at 50 mm skin-to-collimator distance corresponds to a minification factor 1:5. The detector is operated at a single low-energy threshold of about 20 keV. Results: For 99 mTc, at 50 mm distance, a background-subtracted sensitivity of 6.5×10-3 cps/kBq and a system spatial resolution of 5.5 mm FWHM were obtained for the 0.94 mm pinhole; corresponding values for the 2.1 mm pinhole were 3.3×10-2 cps/kBq and 12.6 mm. The dark count rate was 0.71 cps. Clinical images in three patients with melanoma indicate detection of the SLNs with acquisition times between 60 and 410 s with an injected activity of 26 MBq 99 mTc and prior localization with standard gamma camera lymphoscintigraphy. Conclusions: The laboratory performance of this imaging probe is limited by the pinhole collimator performance and the necessity of working in minification due to the limited detector size. However, in clinical operative conditions, the CdTe imaging probe was effective in detecting SLNs with adequate resolution and an acceptable sensitivity. Sensitivity is expected to improve with the future availability of a larger CdTe detector permitting operation at shorter distances from the patient skin. [ABSTRACT FROM AUTHOR]

The efficiency of high-resolution pixel detectors for hard X-rays is nowadays one of the major criteria which drives the feasibility of imaging experiments and in general the performance of an experimental station for synchrotron-based microtomography and radiography. Here the luminescent screen used for the indirect detection is focused on in order to increase the detective quantum efficiency: a novel scintillator based on doped Lu2SiO5 (LSO), epitaxially grown as thin film via the liquid phase epitaxy technique. It is shown that, by using adapted growth and doping parameters as well as a dedicated substrate, the scintillation behaviour of a LSO-based thin crystal together with the high stopping power of the material allows for high-performance indirect X-ray detection. In detail, the conversion efficiency, the radioluminescence spectra, the optical absorption spectra under UV/visible-light and the afterglow are investigated. A set-up to study the effect of the thin-film scintillator's temperature on its conversion efficiency is described as well. It delivers knowledge which is important when working with higher photon flux densities and the corresponding high heat load on the material. Additionally, X-ray imaging systems based on different diffraction-limited visible-light optics and CCD cameras using among others LSO-based thin film are compared. Finally, the performance of the LSO thin film is illustrated by imaging a honey bee leg, demonstrating the value of efficient high-resolution computed tomography for life sciences [ABSTRACT FROM AUTHOR]

We present results obtained with a new scintillation detector of secondary electrons for the variable pressure scanning electron microscope. A detector design is based on the positioning of a single crystal scintillator within a scintillator chamber separated from the specimen chamber by two apertures. This solution enables us to decrease the pressure to several Pa in the scintillator chamber while the pressure in the specimen chamber reaches values of about 1000 Pa (7.5 Torr). Due to decreased pressure, we can apply a potential of the order of several kV to the scintillator, which is necessary for the detection of secondary electrons. Simultaneously, the two apertures at appropriate potentials of the order of several hundreds of volts create an electrostatic lens that allows electrons to pass from the specimen chamber to the scintillator chamber. Results indicate a promising utilization of this detector for a wide range of specimen observations. [ABSTRACT FROM AUTHOR]

Here, we report a new polycrystalline ceramic scintillator for possible use in γ-ray detection and medical imaging applications. The goal was to develop a cerium-doped spinel (MgAl2O4:Ce), which can be processed utilizing ceramic forming techniques. High-purity MgAl2O4 powders were used as the starting materials. Lithium fluoride (LiF) was used as a sintering aid and CeO2 powder was used as the dopant. The mixed and dried powders were hot pressed in a vacuum environment to achieve high-density MgAl2O4:Ce. The hot-pressed sample shows a transparent polycrystalline appearance. In-line transmission was measured to determine the transparency of the structure. Microstructures were characterized using X-ray diffraction and scanning electron microscopy. Fluorescence absorption and emission peaks were also measured in addition to the decay time measurement. [ABSTRACT FROM AUTHOR]

Comparatively high gadolinium contents are of primary importance for (Y,Gd)2O3:Eu scintillators because of expected higher scintillation intensity and higher light output of the materials. Transparent Y0.6Gd1.34Eu0.06O3 ceramic, with a high gadolinium composition of ∼67 mol%, has been fabricated via vacuum sintering using synthesized sinterable powders. The precursor powder was coprecipitated with ammonium hydrogen carbonate as the precipitant and the powder calcined at 1100°C showed the best sintering activity. Transparent Y0.6Gd1.34Eu0.06O3 ceramic, exhibiting an in-line transmittance of 66.7% at 610 nm, was obtained by vacuum sintering at 1670°C for 2 h. Under X-ray excitation, the ceramic exhibited characteristic emissions of the Eu3+ ions. [ABSTRACT FROM AUTHOR]

Purpose: Previously, we demonstrated the potential of positron emission tomography detectors consisting of monolithic scintillation crystals read out by arrays of solid-state light sensors. We reported detector spatial resolutions of 1.1–1.3 mm full width at half maximum (FWHM) with no degradation for angles of incidence up to 30°, energy resolutions of ∼11% FWHM, and timing resolutions of ∼2 ns FWHM, using monolithic LYSO:Ce3+ crystals coupled to avalanche photodiode (APD) arrays. Here we develop, validate, and demonstrate a simple model of the detector point spread function (PSF) of such monolithic scintillator detectors. Methods: A PSF model was developed that essentially consists of two convolved components, one accounting for the spatial distribution of the energy deposited by annihilation photons within the crystal, and the other for the influences of statistical signal fluctuations and electronic noise. The model was validated through comparison with spatial resolution measurements on a detector consisting of an LYSO:Ce3+ crystal read out by two APD arrays. Results: The model is shown to describe the measured detector spatial response well at the noise levels found in the experiments. In addition, it is demonstrated how the model can be used to correct the measured spatial response for the influence of the finite diameter of the annihilation photon beam used in the experiments, thus obtaining an estimate of the intrinsic detector PSF. Conclusions: Despite its simplicity, the proposed model is an accurate tool for analyzing the detector PSF of monolithic scintillator detectors and can be used to estimate the intrinsic detector PSF from the measured one. [ABSTRACT FROM AUTHOR]

We discuss glass as an engineered material in its traditional role to control the propagation of and to spectrally modify light in the performance of optical functions. Next, we consider fluorescence, which provides the capability to convert absorbed light of a particular frequency to emitted light of a lower frequency and as a necessary condition for light amplification through spontaneous emission of radiation. Finally, we consider glass in the framework of high-energy particle physics experiments, including its use as a scintillator material and as a Cerenkov radiation detector. [ABSTRACT FROM AUTHOR]

Charge-coupled devices (CCD) are nowadays commonly utilized in transmission electron microscopy (TEM) for applications in life sciences. Direct access to digitized images has revolutionized the use of electron microscopy, sparking developments such as automated collection of tomographic data, focal series, random conical tilt pairs and ultralarge single-particle data sets. Nevertheless, for ultrahigh-resolution work photographic plates are often still preferred. In the ideal case, the quality of the recorded image of a vitrified biological sample would solely be determined by the counting statistics of the limited electron dose the sample can withstand before beam-induced alterations dominate. Unfortunately, the image is degraded by the non-ideal point-spread function of the detector, as a result of a scintillator coupled by fibre optics to a CCD, and the addition of several inherent noise components. Different detector manufacturers provide different types of figures of merit when advertising the quality of their detector. it is hard for most laboratories to verify whether all of the anticipated specifications are met. In this report, a set of algorithms is presented to characterize on-axis slow-scan large-area CCD-based TEM detectors. These tools have been added to a publicly available image-processing toolbox for MATLAB. Three in-house CCD cameras were carefully characterized, yielding, among others, statistics for hot and bad pixels, the modulation transfer function, the conversion factor, the effective gain and the detective quantum efficiency. These statistics will aid data-collection strategy programs and provide prior information for quantitative imaging. The relative performance of the characterized detectors is discussed and a comparison is made with similar detectors that are used in the field of X-ray crystallography. [ABSTRACT FROM AUTHOR]

Europium (Eu) was found to act as a solid-state sintering aid in Y2O3 optical ceramics by controlling ionic diffusivity, which in turn leads to enhanced optical transparency. Transparent ceramic samples of Eu-doped Y2O3, with no additional additives, were sintered by uniaxial vacuum hot pressing under 40 MPa and maximum temperature of 1580°C. Optical attenuation was found to decrease with increasing Eu concentrations between 0 and 5 at% for ceramics processed under the same sintering conditions. In order to study the effect of Eu concentration on ceramic densification, the strain rate and grain size during sintering at constant temperature and varied pressure were measured. A diffusional flow densification model was used to derive instantaneous effective diffusion constants for the densification process. Diffusion constants were found to increase with increasing Eu concentration according to a log–linear relationship. Eu2+ was detected in samples after hot pressing through fluorescence spectroscopy, and the extrinsic defect chemistry was found to be dominated by the reduced Eu in solid solution with Y2O3. A sintering model with diffusion rate limited by yttrium interstitial transport and controlled by the incorporation of Eu2+ onto the cation sublattice was found to be in good agreement with experimental diffusivity data. [ABSTRACT FROM AUTHOR]

Purpose: The therapeutic outcome of the therapy with ophthalmic applicators is highly dependent on the application of a sufficient dose to the tumor, whereas the dose applied to the surrounding tissue needs to be minimized. The goal for the newly developed apparatus described in this work is the determination of the individual applicator surface dose rate distribution with a high spatial resolution and a high precision in dose rate with respect to time and budget constraints especially important for clinical procedures. Inhomogeneities of the dose rate distribution can be detected and taken into consideration for the treatment planning. Methods: In order to achieve this, a dose rate profile as well as a surface profile of the applicator are measured and correlated with each other. An instrumental setup has been developed consisting of a plastic scintillator detector system and a newly designed apparatus for guiding the detector across the applicator surface at a constant small distance. It performs an angular movement of detector and applicator with high precision. Results: The measurements of surface dose rate distributions discussed in this work demonstrate the successful operation of the measuring setup. Measuring the surface dose rate distribution with a small distance between applicator and detector and with a high density of measuring points results in a complete and gapless coverage of the applicator surface, being capable of distinguishing small sized spots with high activities. The dosimetrical accuracy of the measurements and its analysis is sufficient (uncertainty in the dose rate in terms of absorbed dose to water is <7%), especially when taking the surgical techniques in positioning of the applicator on the eyeball into account. Conclusions: The method developed so far allows a fully automated quality assurance of eye applicators even under clinical conditions. These measurements provide the basis for future calculation of a full 3D dose rate distribution, which then can be used as input for a refined clinical treatment planning system. The improved dose rate measurements will facilitate a clinical study, which could correlate the therapeutic outcome of a brachytherapy treatment with an applicator and its individual dose rate distribution. [ABSTRACT FROM AUTHOR]

Purpose: A new concept of indirect conversion flat-panel imager with avalanche gain and field emitter array (FEA) readout is being investigated. It is referred to as scintillator avalanche photoconductor with high resolution emitter readout (SAPHIRE). The present work investigates the temporal performance, i.e., lag, of SAPHIRE. Methods: Since the temporal performance of the x-ray detection materials, i.e., the structured scintillator and avalanche amorphous selenium (a-Se) photoconductor, has been studied previously, the investigation is focused on lag due to the FEA readout method. The principle of FEA readout is similar to that of scanning electron beam readout used in camera tubes, where the dominant source of lag is the energy spread of electrons. Since the principles of emission and beam focusing methods for FEA are different from thermionic emission used in camera tubes, its electron beam energy spread and hence lag is expected to be different. In the present work, the energy spread of the electrons emitted from a FEA was investigated theoretically by analyzing different contributing factors due to the FEA design and operations: The inherent energy spread of field emission, the FEA driving pulse delay, and the angular distribution of emitted electrons. The electron energy spread determined the beam acceptance characteristic curve of the photoconductive target, i.e., the accepted beam current (Ia) as a function of target potential (Vt), from which lag could be calculated numerically. Lag calculation was performed using FEA parameters of two prototype HARP-FEA image sensors, and the results were compared with experimental measurements. Strategies for reducing lag in SAPHIRE were proposed and analyzed. Results: The theoretical analysis shows that the dominant factor for lag is the angular distribution of electrons emitted from the FEA. The first frame lags for two prototype sensors with 4 and 25 μm HARP layer thicknesses were 62.1% and 9.1%, respectively. A lag clearance procedure can be implemented by turning on all the FEA pixels simultaneously between subsequent frames without negative impact of readout speed. For large-area SAPHIRE, the bias electrode for the HARP needs to be divided into strips to allow parallel readout. With typical cardiac detector parameters, SAPHIRE with 128 parallel strips can provide real-time readout (30 frames/s) with first frame lag of ∼4%. Conclusions: The investigation of lag in SAPHIRE shows that the angular distribution of emitted electrons from FEA can result in substantial lag if the readout was performed pixel by pixel. Effective strategies for reducing lag include dividing the bias electrode into multiple strips to allow parallel readout and the incorporation of rapid charge clearance procedure between subsequent frames or rows. [ABSTRACT FROM AUTHOR]

Scintillation dosimetry with optical fiber readout [fiber optic dosimetry (FOD)] requires accurate measurement of light intensity. It is therefore vulnerable to loss of calibration if any changes occur in the efficiency of the optical pathway between the scintillator and the light detector. The authors show in this article that common types of errors that arise during clinical use for brachytherapy applications can be quantified using a light emitting diode to stimulate the scintillator, the so-called LED-FOD method, in an integrated and easy-to-use control unit that incorporates a compact peripheral component interconnect extension for instrumentation. Common sources of error include bending and mechanical compression of the fiber optic components and changes in the temperature of the scintillator. The authors show that the method can detect all the common errors studied in this work and that different types of errors can result in different correlations between the LED stimulated signal and the brachytherapy source signal. For a single-type error the LED-FOD can be used easily for system diagnosis and validation with the possibility to correct the dosimeter reading if the correlation between the LED stimulated signal and the brachytherapy source signal can be defined. For more complex errors, resulting from two or more errors occurring simultaneously, the LED-FOD method can also allow the clinician to make a judgment on the reliability of the dosimeter reading. This self-checking method can enhance the clinical robustness of the FOD for achieving accurate dose control. [ABSTRACT FROM AUTHOR]

The authors report on the performance of two small field of view, compact gamma cameras working in single photon counting in planar imaging tests at 122 and 140 keV. The first camera is based on a LaBr3:Ce scintillator continuous crystal (49×49×5 mm3) assembled with a flat panel multianode photomultiplier tube with parallel readout. The second one belongs to the class of semiconductor hybrid pixel detectors, specifically, a CdTe pixel detector (14×14×1 mm3) with 256×256 square pixels and a pitch of 55 μm, read out by a CMOS single photon counting integrated circuit of the Medipix2 series. The scintillation camera was operated with selectable energy window while the CdTe camera was operated with a single low-energy detection threshold of about 20 keV, i.e., without energy discrimination. The detectors were coupled to pinhole or parallel-hole high-resolution collimators. The evaluation of their overall performance in basic imaging tasks is presented through measurements of their detection efficiency, intrinsic spatial resolution, noise, image SNR, and contrast recovery. The scintillation and CdTe cameras showed, respectively, detection efficiencies at 122 keV of 83% and 45%, intrinsic spatial resolutions of 0.9 mm and 75 μm, and total background noises of 40.5 and 1.6 cps. Imaging tests with high-resolution parallel-hole and pinhole collimators are also reported. [ABSTRACT FROM AUTHOR]

Compounds containing rare earths are of increasing technological interest especially because of their unique mechanical, magnetic, electrical, and optical properties. Among them, rare earth oxyorthosilicates are attractive scintillators for γ- and X-ray spectroscopy and detection. However, there are many structural aspects of those compounds that are not clear. In this research, the structure parameters for Sc2Si2O5, X2-polymorph, have been refined from powder X-ray diffraction (XRD) data and the 29Si MAS NMR spectrum is reported for the first time. X2-Sc2SiO5 polymorph was synthesized by the sol–gel method and characterized by XRD and 29Si MAS NMR. The XRD pattern was indexed in a monoclinic unit cell with space group I2/ c; the resulting unit cell parameters were a=9.9674(2) Å, b=6.4264(9) Å, c=12.0636(2) Å, and β=103.938(1)°. The 29Si MAS NMR spectrum showed a unique signal at −79.5 ppm, compatible with the unique Si crystallographic site in the unit cell. Finally, the band valence method has been applied to the calculation of a “shift parameter,” which is correlated with the NMR chemical shift. [ABSTRACT FROM AUTHOR]

Compounds containing rare earths are of increasing technological interest especially because of their unique mechanical, magnetic, electrical, and optical properties. Among them, rare earth oxyorthosilicates are attractive scintillators for γ- and X-ray spectroscopy and detection. However, there are many structural aspects of those compounds that are not clear. In this research, the structure parameters for Sc2Si2O5, X2-polymorph, have been refined from powder X-ray diffraction (XRD) data and the 29Si MAS NMR spectrum is reported for the first time. X2-Sc2SiO5 polymorph was synthesized by the sol–gel method and characterized by XRD and 29Si MAS NMR. The XRD pattern was indexed in a monoclinic unit cell with space group I2/ c; the resulting unit cell parameters were a=9.9674(2) Å, b=6.4264(9) Å, c=12.0636(2) Å, and β=103.938(1)°. The 29Si MAS NMR spectrum showed a unique signal at −79.5 ppm, compatible with the unique Si crystallographic site in the unit cell. Finally, the band valence method has been applied to the calculation of a “shift parameter,” which is correlated with the NMR chemical shift. [ABSTRACT FROM AUTHOR]