BGO Crystals Research Articles

Performance of the diamond active target prototype for the PADME experiment at the DA[formula omitted]NE BTF

The PADME experiment at the DAΦNE Beam-Test Facility (BTF) is designed to search for the gauge boson of a new U(1) interaction in the process e+e−→γ+A′, using the intense positron beam hitting a light target. The A′, usually referred as a dark photon, is assumed to decay into invisible particles of a secluded sector and it can be observed by searching for an anomalous peak in the spectrum of the missing mass measured in events with a single photon in the final state. The measurement requires the determination of the 4-momentum of the recoil photon, performed by a homogeneous, highly segmented BGO crystals calorimeter. A significant improvement of the missing mass resolution is possible using an active target capable of determining the average position of the positron pulse with a resolution of less than 1 mm. This report presents the performance of a real size (2 × 2 cm2) PADME active target made of a thin (50 μm) diamond sensor, with graphitic strips produced via laser irradiation on both sides. The measurements are based on data collected in a beam test at the BTF in November 2015.

Evaluation of Crystals’ Morphology on Detection Efficiency Using Modern Classification Criterion and Monte Carlo Method in Nuclear Medicine

Crystals used in medical imaging systems play a key role in obtaining images for the improvement of diagnoses in medicine. We investigated crystal material characteristics in detection efficiency, and a reliable definition of efficiency proposed for improving spatial resolution. In this study, bismuth germanate (BGO), lutetium oxyortho silicate, gadolinium silicate, and lutetium yttrium oxyortho silicate crystals have been evaluated to compare their special characteristics using Monte Carlo simulation. Additionally, a new criterion is introduced as scattering frequency at which the ratio of the number of Compton interaction to the minimum traversed distance of photons in crystal is suggested. This frequency is based on random numbers, Compton scattering, energy of γ-ray, geometry and material of crystal. The sensitivity of crystals as a function of crystal width at various incident angles of the photon is investigated. The simulated results have demonstrated that at a distinct width of crystal, the detection efficiency of the BGO crystal was more than that of other crystals in which the amount of scatter and random coincidences decreased. Crystal width at various applications, however, must be optimized with respect to the trade off among the signal-to-noise ratio, spatial and temporal resolutions, efficiency, and the untrue coincidences. Determining crystal width and material may be useful in collimator design to improve spatial resolution and efficiency.

Moh’s hardness Scale and micro vicker’s hardness study of bgo and lyso inorganic scintillators

BGO and LYSO inorganic scintillation crystals were chosen in this paper for density and hardness properties investigation. Moh’s hardness scale was determined by scratching test which of the standard minerals. The micro vicker’s hardness was measured with a diamond indenter and the test load was used at 0.1 kgf. The results show that, the moh’s hardness scale of LYSO crystal are higher than BGO crystal which correspond with micro vicker’s hardness values. The density of scintillation crystals were measured and found to be 7.1 g/cm3 for BGO crystal and 7.15 g/cm3 for LYSO crystal.

Determination of Moisture Content in Coke with 239Pu–Be Neutron Source and BGO Scintillation Gamma Detector

A series of experiments has been conducted at the Frank Laboratory of Neutron Physics (FLNP) of the Joint Institute for Nuclear Research (JINR) in order to study the possibility of determining the moisture content of coke using a standard neutron source. The proposed method is based on a measurement of the spectrum of prompt γ rays emitted when samples are irradiated by fast and/or thermal neutrons. The moisture content is determined from the area of the peaks of characteristic γ rays produced in the radiative capture of thermal neutrons by the proton (Eγ = 2.223 MeV) and inelastic scattering of fast neutrons by 16O (Eγ = 6.109 MeV). The 239Pu–Be neutron source (〈E n 〉 ~ 4.5 MeV) with an intensity of ~5 × 106 n/s was used to irradiate the samples under study. A scintillation detector based on a BGO crystal was used to register the characteristic γ radiation from the inelastic fast neutron scattering and slow (thermal) neutron capture. This paper presents the results of humidity measurement in the range of 2–50% [1, 2].

Energy Broadening Model for BGO Array Crystal from 0.059 to 1.332 MeV

The energy resolution and energy broadening parameters are of great importance as far as scintillator detector is concerned. At present, BGO crystal due to its high density, high yield of photoelectric absorption, availability and cost is used in particle physics and medical imaging system especially in positron emission tomography (PET). The purpose of this study is to calculate the Gaussian energy broadening parameters of a 10 × 10 BGO array in order to use it in simulation for analysis of its spectral response in the presence of gamma rays in a wide range of energies. The Gaussian energy broadening parameters were extracted from the experimental spectrum to use them as the input parameters in MCNP4c code. The simulated response of the detector employing these parameters showed a good agreement with the experimental data.

Calorimetry of the CMD-3 detector

The CMD-3 detector has been collecting data since 2010 at the e+e− collider VEPP-2000 in the Budker Institute of Nuclear Physics. VEPP-2000 uses the novel round beam technique and provides high luminosity in a wide c.m.energy range from 0.32 to 2 GeV. The physics goal of the CMD-3 experiment is a study of the e+e− annihilation into hadrons. CMD-3 is a general-purpose detector, which provides high efficiency for both charged and neutral particles. The electromagnetic calorimeter consists of the barrel calorimeter based on liquid xenon and CsI crystals, and the endcap calorimeter based on BGO crystals. The main parameters of the calorimeters are presented.

Performances of Crystal Scintillators in a Severe Radiation Environment Caused by Gamma Rays

Because of their superb energy resolution and detection efficiency crystal scintillators are widely used in high energy and nuclear physics experiments. A crucial issue is radiation damage. We report an investigation on γ-ray induced radiation damage in crystal scintillators of large size, including BaF2, BGO, CeF3, pure CsI, LSO/LYSO/LFS and PWO with an integrated dose up to 340 Mrad at a dose rate up to 1 Mrad/h. Optical and scintillation properties of these crystal samples were measured before and after irradiations. The result shows that pure CsI crystals have good radiation hardness below 100 krad. BaF2, BGO and LYSO crystals show good radiation hardness beyond 1 Mrad. In terms of light output degradation LSO/LYSO/LFS is clearly the best among all scintillation crystals.

Performance of Crystal Scintillators in a Severe Radiation Environment Caused by Protons

Future high energy physics experiments at the energy and intensity frontiers will face challenges from a severe radiation environment caused by both ionization dose and charged and neutral hadrons. This paper reports an investigation on proton induced radiation damage in various crystal scintillators. Large size BGO, LFS and PWO crystals of 18 to 22 cm long were irradiated by 800 MeV protons up to 3 × 1015 p/cm2 at the WNR facility of LANSCE with longitudinal transmittance measured in situ. LYSO plates of 14 × 4 × 1.5 mm3 were irradiated by 24 GeV protons up to 8.2 × 1015 p/cm2 at the IRRAD facility of CERN. Degradations in both transmittance and light output are reported. The results show an excellent radiation hardness of LYSO/LFS crystals against charged hadrons.

Highly improved operation of monolithic BGO-PET blocks

In PET scanners both scintillation crystals and photosensors are key components defining the system's performance and cost. Original PET systems used BGO or NaI(Tl) scintillators but achieved limited performance due to its slow decay and relatively low light output. Moreover, NaI(Tl) has low stopping power for 511 keV annihilation photons. In this study we report the possibility to reintroduce BGO crystals, and in particular in the form of monolithic blocks, especially suitable for low-dose large-size PET scanners, offering significantly improved sensitivity at a highly reduced cost compared to LYSO type fast scintillators. We have studied the performance of a monolithic BGO block as large as 50 × 50 × 15 mm3 with black-painted lateral walls to reduce lights spread, enabling accurate photon depth of interaction (DOI) measurements. A directional optical layer, called retro-reflector, was coupled to the entrance face bouncing back the scintillation light in the direction of the emission source and, therefore, adding to the light signal while preserving the narrow light cone distribution. Four configurations namely 12 × 12 and 16 × 16 SiPM arrays (3 mm × 3 mm each) as photosensors, with or without a nanopattern treatment at the crystal exit face, have been studied. This structure consisted of a thin layer of a specific high refractive index material shaped with a periodic nanopattern, increasing the scintillation light extraction. The readout returned information for each SiPM row and column, characterizing the X-Y light distribution projections. We have studied the detector spatial resolution using collimated 22Na sources at normal incidence. The DOI resolution was evaluated using collimated gamma beams with lateral incidence. The overall best detector performance was obtained for the 16× 16 SiPM array offering higher readout granularity. We have determined the spatial resolution for 3 separated DOI layers, obtaining the best results for the DOI region near to the photosensor.

Monte Carlo optimization of a Compton suppression system for gamma-ray diagnosis of combustion plasma

The use of Gamma-ray spectrometers provides very important diagnostic tools in large-scale tokamak experiments. In this study, the Geant4 toolkit was used to simulate a Compton suppression system based upon a High-Purity Germanium (HPGe) primary detector in order to gain the optimal sizes for the construction of the system for 0.1 MeV–10 MeV γ-rays which are emitted from the HL-2A tokamak. BGO crystal is selected for the anti-coincidence secondary detector. Simulation results show that when the closer the HPGe primary detector is set to the beam entrance and the smaller the entrance size is, the higher the Compton Suppression Factors (CSFs) are. Moreover, adding a BGO crystal to the back of the HPGe detector can also improve the CSFs, and the CSFs increase more significantly with the higher γ-ray energies. And a BGO crystal with the thickness of 25 mm in front of the HPGe detector can reach a good suppression effect. For the BGO hollow cylinder, the CSFs do not increase obviously after its thickness reaches 60–70 mm. Finally, optimal parameters for the Compton suppression system are suggested. Moreover, for the optimal Compton suppression system, γ-rays produced by neutrons which are also one of fusion products, can be well suppressed.

Feasibility of Using Crystal Geometry for a DOI Scintillation Detector.

We have used simulations and measurements to investigate the feasibility of using slanted scintillator crystal geometries as means to provide depth-of-interaction (DOI) information for a pixelated gamma ray imaging detector. The simulations were performed to estimate the fraction of scintillation light detected by the photodetector as a function of interaction location along the height of crystals with different geometries. In addition, physical measurements of the light output for these crystal geometries were obtained from individual crystals coupled to a solid state photodetector (Philips digital-SiPM DPC-3200). In agreement with previous work, we found a change in light output in the slanted region of the crystals compared to the rectangular region. The results from this study indicate the potential of using slanted crystals to gather DOI information based on light output changes as a function of the location of interaction. An examination of the measured energy spectra for the geometries evaluated here, suggests that for BGO crystals somewhere between 2 or 3 DOI bins could be implemented. Based on these results, we conceived a design for a DOI detector module that consists of two slanted crystals, each read-out by separate SiPM pixels.

Evaluation of clustering algorithms at the < 1 GeV energy scale for the electromagnetic calorimeter of the PADME experiment

A possible solution to the Dark Matter problem postulates that it interacts with Standard Model particles through a new force mediated by a “portal”. If the new force has a U(1) gauge structure, the “portal” is a massive photon-like vector particle, called dark photon or A’. The PADME experiment at the DAΦNE Beam-Test Facility (BTF) in Frascati is designed to detect dark photons produced in positron on fixed target annihilations decaying to dark matter (e+e-→γA′) by measuring the final state missing mass. One of the key roles of the experiment will be played by the electromagnetic calorimeter, which will be used to measure the properties of the final state recoil γ. The calorimeter will be composed by 616 21×21×230 mm3 BGO crystals oriented with the long axis parallel to the beam direction and disposed in a roughly circular shape with a central hole to avoid the pile up due to the large number of low angle Bremsstrahlung photons. The total energy and position of the electromagnetic shower generated by a photon impacting on the calorimeter can be reconstructed by collecting the energy deposits in the cluster of crystals interested by the shower. In PADME we are testing two different clustering algorithms, PADME-Radius and PADME-Island, based on two complementary strategies. In this paper we will describe the two algorithms, with the respective implementations, and report on the results obtained with them at the PADME energy scale (< 1 GeV), both with a GEANT4 based simulation and with an existing 5×5 matrix of BGO crystals tested at the DAΦNE BTF.

GEANT4-based full simulation of the PADME experiment at the DAΦNE BTF

A possible solution to the dark matter problem postulates that dark particles can interact with Standard Model particles only through a new force mediated by a “portal”. If the new force has a U(1) gauge structure, the “portal” is a massive photon-like vector particle, called dark photon or A′. The PADME experiment at the DAΦNE Beam-Test Facility (BTF) in Frascati is designed to detect dark photons produced in positron on fixed target annihilations decaying to dark matter (e+e-→γA′) by measuring the final state missing mass. The experiment will be composed of a thin active diamond target where a 550 MeV positron beam will impinge to produce e+e- annihilation events. The surviving beam will be deflected with a magnet while the photons produced in the annihilation will be measured by a calorimeter composed of BGO crystals. To reject the background from Bremsstrahlung gamma production, a set of segmented plastic scintillator vetoes will be used to detect positrons exiting the target with an energy lower than that of the beam, while a fast small angle calorimeter will be used to reject the e+e-→γγ(γ) background. To optimize the experimental layout in terms of signal acceptance and background rejection, the full layout of the experiment was modelled with the GEANT4 simulation package. In this paper we will describe the details of the simulation and report on the results obtained with the software.

Geometric alignment of the CMD-3 endcap electromagnetic calorimeter using events of two-quantum annihilation

Since 2010 the electromagnetic endcap calorimeter based on BGO crystals is used in experiments as one of the systems of the CMD-3 detector. The spacial resolution is one of crucial parameters of the calorimeter. Inaccurate knowledge of the real calorimeter position can limit the resolution. In this work the alignment of the center of the calorimeter with respect to the tracking system of the CMD-3 detector has been performed using events of two-quantum annihilation. The alignment technique that has been used to determine the position of the calorimeter is described. Finally, the improvement in spacial resolution of the calorimeter after applying the correction for the real calorimeter position is shown.

Performance of the PADME Calorimeter prototype at the DAΦNE BTF

The PADME experiment at the DAΦNE Beam-Test Facility (BTF) aims at searching for invisible decays of the dark photon by measuring the final state missing mass in the process e+e−→γ+A′, with A′ undetected. The measurement requires the determination of the 4-momentum of the recoil photon, performed using a homogeneous, highly segmented BGO crystals calorimeter. We report the results of the test of a 5×5 crystals prototype performed with an electron beam at the BTF in July 2016.

BGO as a hybrid scintillator / Cherenkov radiator for cost-effective time-of-flight PET

Due to detector developments in the last decade, the time-of-flight (TOF) method is now commonly used to improve the quality of positron emission tomography (PET) images. Clinical TOF-PET systems based on L(Y)SO:Ce crystals and silicon photomultipliers (SiPMs) with coincidence resolving times (CRT) between 325 ps and 400 ps FWHM have recently been developed. Before the introduction of L(Y)SO:Ce, BGO was used in many PET systems. In addition to a lower price, BGO offers a superior attenuation coefficient and a higher photoelectric fraction than L(Y)SO:Ce. However, BGO is generally considered an inferior TOF-PET scintillator. In recent years, TOF-PET detectors based on the Cherenkov effect have been proposed. However, the low Cherenkov photon yield in the order of ∼10 photons per event complicates energy discrimination–a severe disadvantage in clinical PET. The optical characteristics of BGO, in particular its high transparency down to 310 nm and its high refractive index of ∼2.15, are expected to make it a good Cherenkov radiator. Here, we study the feasibility of combining event timing based on Cherenkov emission with energy discrimination based on scintillation in BGO, as a potential approach towards a cost-effective TOF-PET detector. Rise time measurements were performed using a time-correlated single photon counting (TCSPC) setup implemented on a digital photon counter (DPC) array, revealing a prompt luminescent component likely to be due to Cherenkov emission. Coincidence timing measurements were performed using BGO crystals with a cross-section of 3 mm × 3 mm and five different lengths between 3 mm and 20 mm, coupled to DPC arrays. Non-Gaussian coincidence spectra with a FWHM of 200 ps were obtained with the 27 mm3 BGO cubes, while FWHM values as good as 330 ps were achieved with the 20 mm long crystals. The FWHM value was found to improve with decreasing temperature, while the FWTM value showed the opposite trend.

Energy calibration of the barrel calorimeter of the CMD-3 detector

The VEPP-2000 e+e− collider has been operated in the Budker Institute of Nuclear Physics since 2010. Experiments are carried out with two detectors CMD-3 and SND. The calorimetry at the CMD-3 detector is based on three subsystems, two coaxial barrel calorimeters—Liquid Xenon calorimeter and crystal CsI calorimeter, and end cap calorimeter with BGO crystals. This paper describes the procedures of the energy calibration of the combined barrel calorimeter of the CMD-3 detector.

Fabrication, microstructure and luminescence properties of Cr3+ doped Lu3A15O12 red scintillator ceramics

Cr3+ doped Lu3A15O12 transparent ceramics were developed as a new red scintillator ceramics. These ceramics were fabricated by a solid state reaction method under vacuum sintering at temperature range of 1550 °C–1890 °C for 10 h. The doping effect of different Cr3+ concentration (0, 0.1, 0.3 and 0.5 at. %) and air annealing effect were investigated as well. The transparent ceramics (70% @1 mm in visible light range) with dense microstructure were obtained when sintered at 1890 °C for 10 h, the average grain size of 0.3 at.% Cr:LuAG was calculated to be 7 μm. Photo-luminescence spectra revealed that there are two typical excitation bands at around 450 nm and 600 nm which were ascribed to the d–d transitions of Cr3+. 0.3 at. % Cr:LuAG exhibited the optimum photoluminescence intensity and fast decay. Radio-luminescence under X-ray excitation indicated a characteristic Cr3+ emission peaking at 687 nm and 706 nm respectively. The Lu3+Al antisite defects related emission at around 300 nm was observed to decrease with the doping of Cr3+. The steady luminescence efficiency (XEL spectrum integral) is around 20 times of the commercial BGO crystals, more important, the broad and continuous red emission between 600 nm and 800 nm demonstrated Cr:LuAG ceramics a prospective application as new red scintillators.

A Monte Carlo study for optimizing the detector of SPECT imaging using a XCAT human phantom.

Acquiring a high quality image has assigned an important concern for obtaining accurate diagnosis in nuclear medicine. Detector is a critical component of Single Photon Emission Computed Tomography (SPECT) imaging system for giving accurate information from exact pattern of radionuclide distribution in the target organ. The images are strongly affected by the attenuation, scattering, and response of the detector. The conventional detector is mainly made from sodium iodide activated by thallium [NaI(Tl)] in nuclear medicine imaging. This study has planned to introduce a suitable for an optimized SPECT imaging. SIMIND Monte Carlo program was utilized for simulating a SPECT imaging system with a NaI(Tl) detector, and a low-energy high-resolution (LEHR) collimator. The Planar and SPECT scans of a 99mTc point source and also an extended Cardiac-Torso (XCAT) computerized phantom with the experiment and simulated systems were prepared. After verification and validation of the simulated system, the similar scans of the phantoms were compared from the point of view of image quality for 7 scintillator crystals including: NaI(Tl), BGO, YAG:Ce, YAP:Ce, LuAG:Ce, LaBr3 and CZT. The parameters of energy and spatial resolution, and sensitivity of the systems were compared. Images were analyzed quantitatively by SSIM algorithm with Zhou Wang and Rouse/Hemami methods, and also qualitatively by two nuclear medicine specialists. Energy resolutions of the mentioned crystals obtained were: 9.864, 9.8545, 10.229, 10.221, 10.230, 10.131and10.223 percentage for 99mTc photopeak 140 Kev, respectively. Finally, SSIM indexes for the related phantom images were calculated to 0.794, 0.738, 0.735, 0.607, 0.760 and 0.811 compared to the NaI(Tl) acquired images, respectively. Medical diagnosis of the SPECT images of the phantom showed that the system with BGO crystal potentially provides a better detectability for hot and cold lesions in the liver of XCAT phantom. The results showed that BGO crystal has a high sensitivity and resolution, and also provides a better lesion detectability from the point of view of image quality on XCAT phantom.

Development of Dy3+-doped Gd2MoB2O9 phosphor and their luminescence behavior

ABSTRACTIn this work, the Gd2MoB2O9 and Gd2MoB2O9:Dy3+ phosphors have been prepared by solid state reaction and their structural and luminescence properties have been studied. The Gd2O3, MoO3, H3BO3 and Dy2O3 were used as starting materials and homogeneously mixed with appropriate ratio. The mixed materials were pressed at 20 tons and sintered at 800, 850, 900, 950, 1000, 1050 and 1100°C. The Gd2MoB2O9 phase was confirmed by X-ray diffractometer (XRD). The photoluminescence spectra measured by 257 nm excitation show one emission peak at 310 nm corresponding to 6P7/2→8S7/2 of Gd3+, and four emission peaks of Dy3+ at 478, 575, 663 and 754 nm corresponding to 4F9/2 → 6H15/2, 6H13/2, 6H11/2 and 6H9/2 transitions, respectively. The chromaticity coordinates under excitation of λex = 352 nm are (0.48, 0.42), which lies in the white region of CIE 1931 chromaticity diagram. The radioluminescence property was studied by 50 kV, 30 mA X-ray irradiation and compared with commercial BGO crystal. It was found that the integral scintillation efficiency showed 76% of BGO. This result suggests that the developed phosphor may be used in W-LEDs and X-rays imaging applications.