Bismuth Germanium Oxide Crystals Research Articles

Performance Characteristics of a New-Generation Digital Bismuth Germanium Oxide PET/CT System, Omni Legend 32, According to NEMA NU 2-2018 Standards.

The Omni Legend 32 PET/CT system features silicon photomultiplier (SiPM)-based detectors with bismuth germanium oxide crystals and a 32-cm axial field of view (FOV). The present study aimed to determine the performance characteristics of the Omni Legend 32 PET/CT system according to National Electrical Manufacturers Association (NEMA) NU 2-2018 standards. Methods: The PET component of this system comprises 22 detector modules; each module contains 24 detector blocks with 72 bismuth germanium oxide crystals with a volume of 4.1 × 4.1 × 30 mm coupled to 18 SiPM devices with a 6 × 6 mm area, resulting in an axial FOV of 32 cm. The spatial resolution, sensitivity, count rate performance, and image quality delivered by PET were evaluated using the NEMA NU 2-2018 standard. PET images of 2 patients were evaluated to get a visual first impression of the Omni Legend 32 PET/CT system together with Precision DL. Results: The average spatial resolution at 1, 10, and 20 cm from the central axis was 4.3, 5.3, and 6.2 mm, respectively, for filtered backprojection and 3.7, 4.3, and 5.1 mm, respectively, for ordered-subset expectation maximization. The NEMA sensitivity was 47.30 and 47.05 cps/kBq at the axial center of the FOV and at a 10-cm radial offset, respectively. The scatter fraction, count rate accuracy, and peak noise-equivalent count rates were 35.4%, 1.7%, and 501.7 kcps, respectively, at 15.7 kBq/mL. Contrast recovery for the NEMA body phantom from the smallest to the largest sphere ranged from 61.3% to 93.0%, with a background variability of 5.4%-11.7% and a lung error of 5.1% for Q.Clear (β-value, 50). Good patient image quality was obtained with the Omni Legend 32. Conclusion: The Omni Legend 32 has class-leading sensitivity and count rates within the category of whole-body PET systems while maintaining spatial resolution broadly comparable to that of other current SiPM-based PET/CT systems. This combination of properties results in a very good image quality.

Convolutional neural network-based reconstruction for positronium annihilation localization

A novel hermetic detector composed of 200 bismuth germanium oxide crystal scintillators and 393 channel silicon photomultipliers has been developed for positronium (Ps) annihilation studies. This compact 4π detector is capable of simultaneously detecting γ-ray decay in all directions, enabling not only the study of visible and invisible exotic decay processes but also tumor localization in positron emission tomography for small animals. In this study, we investigate the use of a convolutional neural network (CNN) for the localization of Ps annihilation synonymous with tumor localization. Two-γ decay systems of the Ps annihilation from 22Na and 18F radioactive sources are simulated using a GEANT4 simulation. The simulated datasets are preprocessed by applying energy cutoffs. The spatial error in the XY plane from the CNN is compared to that from the classical weighted k-means algorithm centroiding, and the feasibility of CNN-based Ps annihilation reconstruction with tumor localization is discussed.

On the Optical Response of Tellurium Activated Zinc Selenide ZnSe:Te Single Crystal

In this study, the light output of a zinc selenide activated with tellurium (ZnSe: Te) single crystal was measured for X-ray radiography applications. A cubic crystal (10 × 10 × 10 mm) was irradiated using X-rays with tube voltages from 50 to 130 kV. The resulting energy absorption efficiency, detective quantum efficiency, and absolute luminescence efficiency were compared to published data for equally sized GSO: Ce (gadolinium orthosilicate) and BGO (bismuth germanium oxide) crystals. The emitted light was examined to estimate the spectral compatibility with widely used optical sensors. Energy absorption efficiency and detective quantum efficiency of ZnSe: Te and BGO were found to be similar, within the X-ray energies in question. Light output of all three crystals showed a tendency to increase with increasing X-ray tube voltage, but ZnSe: Te stood at least 2 EU higher than the others. ZnSe: Te can be coupled effectively with certain complementary metal–oxide–semiconductors (CMOS), photocathodes, and charge-coupled-devices (CCD), as the effective luminescence efficiency results assert. These properties render the material suitable for various imaging applications, dual-energy arrays included.

Correction method for the readout saturation of the DAMPE calorimeter

The DArk Matter Particle Explorer (DAMPE) is a space-borne high energy cosmic-ray and γ-ray detector which operates smoothly since the launch on December 17, 2015. The bismuth germanium oxide (BGO) calorimeter is one of the key sub-detectors of DAMPE used for energy measurement and electron–proton identification. For events with total energy deposit higher than decades of TeV, the readouts of PMTs coupled on the BGO crystals would become saturated, which results in an underestimation of the energy measurement. Based on detailed simulations, we develop a correction method for the saturation effect according to the shower development topologies and energies measured by neighbouring BGO crystals. The verification with simulated and on-orbit events shows that this method can well reconstruct the energy deposit in the saturated BGO crystal.

Performance of the DAMPE BGO calorimeter on the ion beam test

The DArk Matter Particle Explorer (DAMPE), which is a Chinese space telescope for the precise measurement of high-energy electrons, gamma rays, and nuclei from deep space, was successfully launched on December 17, 2015. The DAMPE electromagnetic calorimeter made of bismuth germanium oxide (BGO) crystals can measure incident hadron energies from 50 GeV to 100 TeV. The calorimeter was tested with ion beams at CERN in 2015. The energy responses to ions from helium to argon are investigated. The result is reproduced by a Monte Carlo simulation based on Geant4 with two physics process models. It shows that the simulation results of a beam test are independent of the physics models adopted. Additionally, quenching effects of the BGO crystal on the ions are observed with this beam test. The quenching attenuations increase with the atomic number and were approximately 7% for boron and 40% for argon.

Information Capacity of Positron Emission Tomography Scanners

Background: The aim of the present study was to assess the upper information content bound of positron emission tomography (PET) images, by means of the information capacity (IC). Methods: The Geant4 Application for the Tomographic Emission (GATE) Monte Carlo (MC) package was used, and reconstructed images were obtained by using the software for tomographic image reconstruction (STIR). The case study for the assessment of the information content was the General Electric (GE) Discovery-ST PET scanner. A thin-film plane source aluminum (Al) foil, coated with a thin layer of silica and with a 18F-fludeoxyglucose (FDG) bath distribution of 1 MBq was used. The influence of the (a) maximum likelihood estimation-ordered subsets-maximum a posteriori probability-one step late (MLE-OS-MAP-OSL) algorithm, using various subsets (1 to 21) and iterations (1 to 20) and (b) different scintillating crystals on PET scanner’s performance, was examined. The study was focused on the noise equivalent quanta (NEQ) and on the single index IC. Images of configurations by using different crystals were obtained after the commonly used 2-dimensional filtered back projection (FBP2D), 3-dimensional filtered back projection re-projection (FPB3DRP) and the (MLE)-OS-MAP-OSL algorithms. Results: Results shown that the images obtained with one subset and various iterations provided maximum NEQ values, however with a steep drop-off after 0.045 cycles/mm. The single index IC data were maximized for the range of 8–20 iterations and three subsets. The PET scanner configuration incorporating lutetium orthoaluminate perovskite (LuAP) crystals provided the highest NEQ values in 2D FBP for spatial frequencies higher than 0.028 cycles/mm. Bismuth germanium oxide (BGO) shows clear dominance against all other examined crystals across the spatial frequency range, in both 3D FBP and OS-MAP-OSL. The particular PET scanner provided optimum IC values using FBP3DRP and BGO crystals (2.4829 bits/mm2). Conclusions: The upper bound of the image information content of PET scanners can be fully characterized and further improved by investigating the imaging chain components through MC methods.

Calibration and irradiation study of the BGO background monitor for the BEAST II experiment

Beam commissioning of the SuperKEKB collider began in 2016. The Beam Exorcism for A STable experiment II (BEAST II) project is particularly designed to measure the beam backgrounds around the interaction point of the SuperKEKB collider for the Belle II experiment. We develop a system using bismuth germanium oxide (BGO) crystals with optical fibers connecting to a multianode photomultiplier tube (MAPMT) and a field-programmable gate array (FPGA) embedded readout board for monitoring the real-time beam backgrounds in BEAST II. The overall radiation sensitivity of this system is estimated to be (2.20±0.26)×10−12 Gy/ADU (analog-to-digital unit) with the standard 10 m fibers for transmission and the MAPMT operating at 700 V. Our γ-ray irradiation study of the BGO system shows that the exposure of BGO crystals to 60Co γ-ray doses of 1 krad has led to immediate light output reductions of 25–40%, and the light outputs further drop by 30–45% after the crystals receive doses of 2–4 krad. Our findings agree with those of the previous studies on the radiation hard (RH) BGO crystals grown by the low thermal gradient Czochralski (LTG Cz) technology. The absolute dose from the BGO system is also consistent with the simulation, and is estimated to be about 1.18 times the equivalent dose. These results prove that the BGO system is able to monitor the background dose rate in real time under extreme high radiation conditions. This study concludes that the BGO system is reliable for the beam background study in BEAST II.

Spectral dependences of the optical absorption in bismuth germanium oxide crystals annealed in vacuum

Results of experimental investigations into the spectral dependences of the light absorption coefficient of an undoped Bi12GeO20 crystal annealed in vacuum at a temperature of 650°С and subsequently annealed in the air atmosphere at temperatures in the range Т АА = 315–590°С are presented for the spectral range 400–1100 nm at room temperature. It is established that the optical absorption of the crystal after temperature annealing in vacuum increases in the entire examined spectral range. Subsequent annealing in air leads to gradual restoration of the initial impurity absorption spectrum in the range from 530 to 1100 nm. The wide band that can be caused by oxygen vacancies is observed in the spectrum of absorption changes induced by annealing in vacuum.

Defects in Cr-doped bismuth germanium oxide crystal irradiated by high energy 235U ions

The present work is devoted to investigation of radiation defects in chromium doped Bi12GeO20 (BGO) single crystals absorbing in the spectral range 0.2…1.1 μm induced under influence of the 235U ions irradiation with energy 9.35 MeV/u and a fluence 5×1011 cm-2. For comparison the changes of absorption spectra during irradiation by light from different sources due as radiation defects creation are studied. The effect of heating in air on the absorption spectrum of irradiated sample is also studied.

Czochralski growth of bismuth germanium silicon oxide (BGSO) single crystal and its characterization

This paper presents the single crystal growth of mixed crystals of bismuth germanium oxide–bismuth silicon oxide from their solid solution by the Czochralski technique. By employing suitable rotation rate, pulling rate and appropriate temperature gradient good quality bismuth germanium silicon oxide crystals (hereinafter abbreviated as BGSO) have been grown. Grown crystal was subjected to the powder and single crystal X-ray diffraction studies. Lattice parameter has been computed from single crystal X-ray diffraction. Differential thermal analysis has been carried out and the melting temperature of the crystal was found to be 1054°C and the composition of the grown crystal has been studied by EDX analysis.

Acousto-optic detection of Bleustein-Gulyaev surface waves propagating on cubic crystals

The interaction of Bleustein-Gulyaev (BG) waves with light propagating in the SAW sagittal plane is investigated theoretically for crystal cuts of gallium arsenide (GaAs) and bismuth germanium oxide (BGO). The diffraction of the transmitted beam is studied versus the angle between the light's wavevector and the normal to the SAW supporting plate (the depth direction along which the SAW attenuates). The experimental results obtained with a BGO crystal are then reported and compared with the above theory.

Morphology of Bi 12GeO 20 crystals grown along the 〈111〉 directions by the Czochralski method

Crystals of bismuth germanium oxide (Bi 12GeO 20 or BGO) have been grown along the 〈111〉 directions by the Czochralski method in air atmosphere. The crystal morphology has been investigated, and the facets have been unambiguously attributed. This morphology is a consequence of the use of (i) a variable rotation rate which enables one to get a convex interface during the whole experiment, and (ii) a slow pulling rate of 0.5 mm/h which allows one to be near-equilibrium conditions and thereby to obtain a near-equilibrium shape. These two conditions which support the morphology of the BGO crystal, permit a better knowledge of previous results.

Low-temperature photochromic response of gallium-doped bismuth germanium oxide

Gallium is one of several dopants that electronically compensate the deep donor responsible for the yellow coloration observed in bismuth germanium oxide (BGO). A series of Ga-doped BGO crystals were grown using the Czochralski method to confirm the formation of a trapped hole center following exposure to near band edge light at low temperatures. The deep donor absorption shoulder disappeared for Ga concentrations in the 3%–4% (melt) range. Excitation at 10 K with 3.3 eV light produces photochromic absorption bands. For low gallium concentrations the photochromic bands were the same as the ones observed in undoped BGO. For concentrations of 4% or more the photoinduced absorption consisted of overlapping bands at 1.1, 1.55, and 2.45 eV. These bands grew uniformly with exposure time and annealed together in the 100–120 K temperature range. By comparison with earlier results on Al-doped BGO and bismuth silicon oxide (BSO), we believe that the 1.1 eV band in BGO:Ga and the 1.0 eV band in BGO:Al (and BSO:Al) are due to trapped hole centers ([GaO4]0 and [AlO4]0, respectively).

Some aspects of growth and characterisation of BSO and BGO crystals

Abstract Bismuth silicon oxide (BSO) and bismuth germanium oxide (BGO) crystals were grown by the Czochralski technique and the various parameters such as crystal rotation rate, pulling rate and growth temperature have been optimised for bubble free growth.

Growth of bismuth silicon oxide and bismuth germanium oxide crystals by the Czochralski technique and their characterization

Photorefractive single crystals of bismuth silicon oxide (Bii2SiO2o) and bismuth germanium oxide (Bi12GeO2o) have been grown using the Czochralski technique. The experimental results are explained with the existing theoretical models. The grown crystals are characterized by x-ray, differential thermal analysis, scanning electron microscopy, IR transmission spectrum, and electron-probe microanalysis.

Growth of bubble-free bismuth silicon oxide and bismuth germanium oxide crystals under conditions of forced convection in the melt

Growth of bubble-free bismuth silicon oxide and bismuth germanium oxide crystals under conditions of forced convection in the melt

Thermally stimulated current studies of bismuth germanium oxide crystal

Thermally stimulated current (TSC) from nominally undoped Bi12GeO20 (BGO) crystals was measured as a function of the uv excitation temperature and time. The results were compared with the previous work on Bi12SiO20 (BSO). The correlation in trapping kinetics among the three major traps observed previously in BSO appears to hold also for BGO; i.e., the shallowest trap acts as a precursor state for electrons to be trapped into the deeper traps. However, an additional finding on the temperature dependence of trap density in the TSC curves of BGO indicates that the simple model proposed earlier is not strictly valid and further study is required.

Stable internal polarization in Bismuth Germanium Oxide crystals

The Bismuth Germanium Oxide (BGO) crystals find a wide application in electrooptical devices where (e.g. PROM) the recording mechanism is the generation and separation of electron-hole pairs. Further, the separated electron-hole pairs reduce the voltage across the crystal. In this connection, the study of internal electric fields induced under electret and photoelectret polarization in the crystal is of great importance.The present paper deals with the stable internal polarization induced by the external electric field and light in BGO crystals. The magnitude of polarization (Q) under different conditions of electret creation (for various EpolTpol, Δt1) that permits choosing the optimum conditions for the maximum internal field of E ∼ 4 105 V/cm to be formed in the dark has been measured. The electret creation in the light results both in the rise of the maximum polarization charge value and of the internal field by an order of magnitude (E ∼ 106 V/cn.). Thus, our measurements have shown that the BGO crys...

Ultrasonic attenuation in single crystals of bismuth germanium oxide at low temperatures

The ultrasonic attenuation of longitudinal acoustic waves in single crystals of bismuth germanium oxide has been measured over a temperature range from 4.2° to 78 °K, using the pulse-echo technique. The frequency range of the impressed phonons was from 10 to 70 MHz. Measurements have been made for phonons propagated along the [100], [110], and [111] crystallographic axes of the specimens. Analysis of the experimental results indicates that the attenuation can be accounted for entirely by the relaxation interaction of mobile charge carriers with the longitudinal electric fields of piezoelectric origin, which accompany the stress waves in the crystal. Based on this analysis, the electromechanical coupling constants obtained from the attenuation data are an order of magnitude smaller than the previously reported values.

The Czochralski growth of doped bismuth‐germanium oxide (BGO) and bismuth‐silicon oxide (BSO) single crystals

AbstractDoped single crystals of BGO and BSO with Cr, Mn, Cu, Ni have been grown. The conditions for the growth of doped single crystals by the Czochralski method have been determined, analyses of distributions of dopants in the crystals have been made. For the Mn, Cr, Cu, doped crystals changes of coloration after illumination with visible light have been observed.