Scintillator Layer Research Articles

Hadronic Showers in a Highly Granular Imaging Calorimeter

Abstract The CALICE collaboration develops highly granular calorimeter prototypes to evaluate technologies for experiments at a future lepton collider. The analogue hadronic calorimeter prototype consists of steel absorber plates interleaved with 38 active plastic scintillator layers which are sub-divided into small tiles. In total 7608 tiles are read out individually via embedded Silicon Photomultipliers. The prototype is one of the first large scale applications of these novel and very promising miniature photodetectors. Since 2006, the calorimeter has been operated in combined test beam setups at DESY, CERN and FNAL. The high-resolution 3D image data with analogue energy information are used to study properties and composition of hadronic showers at a new level of detail. This helps to constrain hadronic shower models through comparisons with model calculations. The spatial shower development and the substructure of the showers, compared to a variety of different Geant 4 shower models including decompositions into individual shower components are presented. Aspects of the energy reconstruction of hadronic showers, such as Particle Flow, are discussed.

High-resolution X-ray Imaging Based on Pixel-structured CsI:Tl Scintillating Screens for Indirect X-ray Image Sensors

We introduce the development of pixel-structured screens with a thallium-doped CsI (CsI:Tl) scintillator for indirect digital X-ray imaging sensors. The indirect-conversion detection method based on the pixel-structured CsI:Tl scintillator provides high spatial resolution X-ray imaging without sacrificing the light spread in thick scintillation layers. The scintillation screens were fabricated by using a vacuum deposition process and filling the CsI:Tl scintillating powders into a two-dimensional pixel-structured silicon array. Pixel structures with 100 μm and 50 μm pixel sizes with wall widths of 20 μm and 200 μm thickness were prepared and the fabricated CsI:Tl scintillating powders were filled into the trench of the pixel structure through a vacuum process. The final scintillation screens with 2.5 cm × 2.5 cm size were prepared and directly coupled to a CCD image sensor with an optical lens for performance evaluation of X-ray imaging. The imaging performance of the samples was investigated in terms of the relative light intensity, the X-ray linearity and the spatial resolution under practical X-ray exposure conditions. These preliminary results imply that pixel-structured CsI:Tl scintillating screens show high spatial resolution by less lateral spread of the emitted visible photons within pixel-structured silicon arrays. However, these X-ray detectors still require improved X-ray sensitivity by coating the reflective layer onto an inner silicon wall surface and filling the scintillating power into pixel structures completely.

Large-area sandwich veto detector with WLS fibre readout for hadron spectroscopy at COMPASS

A sandwich detector composed of scintillator and steel-covered lead layers was introduced in the fixed-target COMPASS experiment at CERN for vetoing events not completely covered by the two-stage magnetic spectrometer. Wavelength shifting fibres glued into grooves in the scintillator tiles serve for fast readout. Minimum ionising particles impinging on the 2 m ×2 m detector outside of a central hole, sparing the spectrometer's entry, are detected with a probability of 98%. The response to charged particles and photons is modelled in detail in Monte Carlo calculations. Figures of merit of the veto trigger in 190 GeV/ c π − + p (or nucleus) experiments are an enrichment of exclusive events in the recorded data by a factor of 3.5 and a false-veto probability of 1%.

SU-F-BRA-02: An Investigation Into Optical Photon Transport Effects on Electronic Portal Imaging Performance Using Geant4

Purpose: To develop a comprehensive Monte Carlo (MC) model of an indirect‐detection electronic portal imaging device(EPID) that can self‐consistently quantify the effect of optical blur on the output signal. Methods: A model of an indirect‐detection EPID was developed using the Geant4 MC toolkit. The EPID was modeled as a series of uniform slabs with thicknesses and material properties obtained from published literature. The model also included a slab of solid water backscatter material directly beyond the EPID rear housing. The standard electromagnetic and optical physics Geant4 modules were incorporated into the model to simultaneously simulate both high energy and optical photontransport relevant for indirect‐detection EPIDs. A narrow, monoenergetic beam of 1 MeV photons was used to generate a line of radiation normally incident on the EPID surface. The beam width was equal to the pixel pitch of 0.4 mm used for scoring particle hits and energy deposition in the gadolinium oxysulfide scintillator and amorphous silicon photodiode layers. Optical and gamma photons were scored separately in the photodiode layer to measure their relative effects on the output signal. Line spread functions (LSFs) were generated indicating the distribution of hits and energy deposited across the scintillator and photodiode planes. Results: The LSFs for optical photon hits in the photodiode array and energy deposition events in the scintillator had a FWHM of approximately 4.7 mm and 0.82 mm, respectively. This indicates a significant increase in image blurring due to optical photon scatter. Conclusions: Our results indicate that modeling optical photontransport may be important when simulating imager performance for an indirect‐detection EPID. Further analysis of calculated LSFs, including determination of the detector modulation transfer function, is required to further quantify imager performance. Cancer Council NSW Research Project Grant RG 11‐06 Cancer Institute NSW Research Equipment Grant 10/REG/1‐20

Baksan Underground Scintillation Telescope upgrade and DAQ of additional layers

The project of the Baksan Underground Scintil- lation Telescope (BUST) upgrade is presented. Additional outer layers of the detectors with fine spatial resolution will be mounted around BUST. Optimal dimensions of a counter, 0.125m◊ 0.125m◊ 0.03m were chosen with a simulation program. The functional diagram of BUSTs DAQ additional layers is presented. Modernization allows us to study the knee region using muon number spectrum measurements. BUST located underground at a depth of 850 m of wa- ter equivalent was designed to solve a number of physical problems which predetermined its construction and location (Alekseev et al., 1998). The telescope is a four-store building with dimensions of 16.7m◊ 16.7m◊ 11.1m and consists of four horizontal and four vertical planes. The total number of detectors is 3180. The analysis of the muon groups registered by BUST gives us an opportunity to obtain information about spectrum and composition of primary cosmic rays in the energy range of 1013 1016 eV (Petkov et al., 2008). The coordinates of fired detectors give the initial information for identification parameters of muon groups (arrival direction and number of muon tracks). In general, the number of muons cross- ing the telescope, n, and the number of the reconstructed muon tracks in a selected event, ntr, should not necessar- ily coincide with each other. When two or more muons are crossing BUST close enough to each other (comparable with the size of the detector), the number of reconstructed muon tracks will be less than the number of muons crossing BUST. Construction of additional external scintillation layers pro-

Performance of the Scintillator-Strip Electromagnetic Calorimeter Prototype for the Linear Collider Experiment

The scintillator-strip electromagnetic calorimeter (ScECAL) is one of fine granular calorimeters proposed to realize Particle Flow Algorithm for the International Linear Collider experiment. The ScECAL is a sandwitch calorimeter with tungsten and scintillator layers, where the scintillator layer consists of plastic scintillator strips which size of 1 cm × 4.5 cm × 0.2 cm with a small photo-sensor (MPPC) attached at the its edge. In alternate scintillator layers, strips are orthogonally aligned to make a virtual 1× 1 cm2 cell with its crossing area. To establish the ScECAL technology, we have built a prototype of the ScECAL which consists of 30 layers of tungsten and scintillator layers with 2160 scintillator strips in total. In 2008 and 2009 the beam test has been performed at Fermilab meson test beam line to evaluate performance of the ScECAL prototype with various types of beams ranging 1 to 32 GeV. As a preliminary result of the beam test in 2008, we have obtained linearity of energy measurement less than 6% from the perfect linear response. Energy resolution is measured to be Although detailed analyses are still ongoing, those results already establishes feasibility of the ScECAL as the fine granular calorimeter. However as the next step to precisely measure even higher energy jets, we will proceed to even more finely segmented calorimeter with 5 mm width scintillator strips.

Electromagnetic response of a highly granular hadronic calorimeter

The CALICE collaboration is studying the design of high performance electromagnetic and hadronic calorimeters for future International Linear Collider detectors. For the hadronic calorimeter, one option is a highly granular sampling calorimeter with steel as absorber and scintillator layers as active material. High granularity is obtained by segmenting the scintillator into small tiles individually read out via silicon photo-multipliers (SiPM). A prototype has been built, consisting of thirty-eight sensitive layers, segmented into about eight thousand channels. In 2007 the prototype was exposed to positrons and hadrons using the CERN SPS beam, covering a wide range of beam energies and angles of incidence. The challenge of cell equalization and calibration of such a large number of channels is best validated using electromagnetic processes. The response of the prototype steel-scintillator calorimeter, including linearity and uniformity, to electrons is investigated and described.

Characterization of scintillator screens for suprathermal ion detection in fusion devices

The luminescence of scintillator screens of Y3Al5O12:Ce3+ (P46), Gd2O2S:Tb3+ (P43), Y2O3:Eu3+ (P56) and SrGa2S4:Eu2+ (TG-Green) has been characterized when irradiated with deuterium ions and α-particles with energies up to 3 MeV. The relative efficiency of the scintillator layers deposited on stainless steel plates has been studied as a function of beam energy and current as well as ion species. The emitted light first increases linearly with beam energy and then saturates. A logarithmic decay of the efficiency with beam current has been observed for all scintillators. Furthermore, the scintillator degradation by high ion dose has been investigated. Among the screens under study, the TG-Green and P46 scintillators are the best suited materials, in terms of relative efficiency and degradation with ion dose, for fast-ion loss detection in fusion devices.

Quasi-pixel structured nanocrystalline Gd2O3(Eu) scintillation screens and imaging performance for indirect X-ray imaging sensors

A novel quasi-pixel structured scintillation screen with nanocrystalline Gd 2 O 3 :Eu particle sizes was introduced for indirect X-ray imaging sensors with high sensitivity and high spatial resolution. A nanocrystalline Gd 2 O 3 :Eu scintillating phosphor with average 100 nm sizes was used as a conversion material for incident X-rays into optical photons. In this work, silicon-based pixel structures with different 100 and 50 μm pixel sizes, 10 μm wall width and 120 μm thickness were fabricated by a standard photolithography and deep reactive ion etching (DRIE) process. The pixelated scintillation screen was fabricated by filling the synthesized nanocrystalline Gd 2 O 3 :Eu scintillating phosphor into pixel-structured silicon arrays, and X-ray imaging performance such as relative light intensity , X-ray to light response and spatial resolution in terms of modulation transfer function (MTF) of the fabricated samples were measured. Although high spatial resolution imaging was largely achieved by pixel-structured nanocrystalline Gd 2 O 3 :Eu scintillation screens, X-ray sensitivity was still low for medical imaging applications. As a result, novel quasi-pixel structured screens with additional thin Gd 2 O 2 S:Tb scintillating layer were proposed for X-ray imaging detector with suitable sensitivity and spatial resolution in comparison with pixel-structured screens, and X-ray imaging performance of quasi-pixel structured nanocrystalline Gd 2 O 3 :Eu scintillating screens was investigated.

Gd-Bearing Composite Scintillators as the New Thermal Neutron Detectors

Composite scintillators based on grains of cerium-doped gadolinium silicate or gadolinium pyrosilicate crystals are studied as thermal neutron detectors. In these scintillators the grains of the single crystal are fixed by a small amount of non-luminescent gel. In contrast to single crystals, there is no technological limitation with composite scintillators in terms of the size or area of the input window. The very thin scintillation layer (one layer of grains with size less than 0.1 mm) in the composite scintillator is enough to detect thermal neutrons with an efficiency of about 20%. In such cases the scintillation signal is mainly recorded in the peak from 33 keV conversion electrons generated in Gd by thermal neutrons. An efficiency value of about 40-50% can be achieved if the total signal of conversion electrons of 33 keV and of Gd K X-rays of 44 keV is taken into account. In this case a thin composite scintillation layer comprising grains with a size less than 0.5 mm is enough.

Modelling of scintillator based flat-panel detectors with Monte-Carlo simulations

Scintillator based flat panel detectors are state of the art in the field of industrial X-ray imaging applications. Choosing the proper system and setup parameters for the vast range of different applications can be a time consuming task, especially when developing new detector systems. Since the system behaviour cannot always be foreseen easily, Monte-Carlo (MC) simulations are keys to gain further knowledge of system components and their behaviour for different imaging conditions. In this work we used two Monte-Carlo based models to examine an indirect converting flat panel detector, specifically the Hamamatsu C9312SK. We focused on the signal generation in the scintillation layer and its influence on the spatial resolution of the whole system. The models differ significantly in their level of complexity. The first model gives a global description of the detector based on different parameters characterizing the spatial resolution. With relatively small effort a simulation model can be developed which equates the real detector regarding signal transfer. The second model allows a more detailed insight of the system. It is based on the well established cascade theory, i.e. describing the detector as a cascade of elemental gain and scattering stages, which represent the built in components and their signal transfer behaviour. In comparison to the first model the influence of single components especially the important light spread behaviour in the scintillator can be analysed in a more differentiated way. Although the implementation of the second model is more time consuming both models have in common that a relatively small amount of system manufacturer parameters are needed. The results of both models were in good agreement with the measured parameters of the real system.

Photon-counting imaging camera for high-resolution X-ray and γ-ray applications

Standard X-ray imaging techniques using CCDs require the integration of thousands of X-ray photonsinto a single image frame. Through the addition of a scintillating layer to the CCD it is possible togreatly increase the X-ray detection efficiency at high energies. Using standard imaging techniqueswith the inclusion of the scintillating layer does, however, leave serious limitations on the spatialresolution achievable due to the spreading of the light generated in the scintillator.The Electron-Multiplying CCD (EM-CCD) shares much of the common architecture of the standardCCD but for the inclusion of a supplementary readout register. This additional high-voltage registerallows the signal electrons to be `multiplied' before reaching the readout node of the CCD, increasingthe signal before any significant noise is introduced. The increase in the signal-to-noise ratio allowsvery low signals to be extracted above the noise floor, leading to the common use of EM-CCDs innight-vision and security applications.Through the coupling of a scintillator to an EM-CCD it is possible to resolve individual X-ray photoninteractions in the scintillator above the noise floor. Without this extra gain these lowsignals would be lost beneath the noise floor. Using various centroiding techniques it is possibleto locate the interaction position of the incident X-ray photon in the scintillator to the sub-pixel level,with measurements here at 59.5 keV giving an initial FWHM of the line spread function of 31μm.This high-resolution, hard X-ray imager has many potential applications in medical and biologicalimaging, where energy discrimination at a high resolution is desired. Further applications includesynchrotron-based research, an area in which high-resolution imaging is essential.

The effect of scintillator response on signal difference to noise ratio in X-ray medical imaging

The aim of the present study was to examine the effect of scintillator material properties on the signal difference to noise ratio (SdNR) under X-ray imaging conditions. To this aim, SdNR was modelled in terms of scintillator material properties such as the quantum detection efficiency (QDE), the intrinsic energy conversion efficiency (ICE) and the light transmission efficiency (LTE). Scintillators were assumed to be in the form of scintillator layers (phosphor screens) with various thicknesses ranging from 70 to 110mg/cm2. Data on the X-ray absorption and optical properties of the scintillators were either calculated from tabulated data, i.e. X-ray attenuation coefficients for QDE estimation, or were obtained from previous experimental studies. It was found that in a wide range of X-ray tube voltages the Gd2O2S:Tb scintillator produced higher SdNR values, while the CsI:Tl scintillator was better at lower voltages (below 65kVp). It was additionally verified that, in the range of X-ray diagnostic energies, SdNR increases with the thickness of the scintillator layer screen. In conclusion, SdNR may be critically affected by scintillator properties and, hence, it may be significantly improved by appropriately selecting the type and thickness of the phosphor screen to be integrated into an imaging system.

Time alignment and calibration of the LHCb calorimeter

The calorimeter system of the LHCb experiment consists of a scintillator layer (SPD), a preshower detector (PS), an electromagnetic calorimeter (ECAL) and a hadronic calorimeter (HCAL), and allows to trigger on hadron, electron and photon candidates. The time synchronization of the four sub-detectors studied with cosmic rays, LHC beam injection tests and LHC proton proton collisions is presented. Energy calibration methods for each subsystem are discussed as well.

The sensitivity and spatial resolution dependence on the microstructures of CsI:Tl scintillation layer for X-ray imaging detectors

Thallium doped cesium iodide (CsI:Tl) scintillator films for the use as a converter for X-ray imaging detectors were fabricated by the thermal deposition method. The microstructures of these scintillating layers were affected by various deposition conditions such as vapor pressure, substrate temperature and post-heat treatment or rapid thermal annealing (RTA). CsI(Tl) scintillator films with various polycrystalline structures were manufactured under different process conditions and prepared for experiments. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate the crystal structure and morphology properties. Light output and spatial resolution of the samples were strongly affected by the microstructures, which are determined by the deposition conditions and post-heat treatment. Imaging characteristics of the various CsI:Tl films were also measured under X-ray exposure conditions by coupling them to a CCD image sensor.

Beam Test of Finely Segmented Scintillator/Tungsten Calorimetry Prototype

In the International Linear Collider (ILC), Particle Flow Algorithm (PFA) plays an important role in achieving excellent jet energy resolution at the level of 30%/√E. In order to achieve this level of resolution, the calorimeter is required to be finely segmented to identify individual particles inside jets. Fine segmentations can be achieved by a consecutive layer structure with scintillator-strips and tungsten. To establish technologies for such scintillator-strip electromagnetic calorimeter (ScECAL), prototypes have been built and tested. The latest prototype has a scintillator strips in successive orthogonal scintillator layers resulting in 1 × 1 cm2 cell size. The strips were produced with the extrusion method. To read out the signal from all the individual strips, Multi Pixel Photon Counter (MPPC) with 1600 pixels has been attached at one side of each strip. The physical size of the prototype is 18 × 18 cm2 with 30 pairs of strips and tungsten layers. The total number of channels is 2160. All the strips and MPPCs have been tested before the prototype was fabricated. The prototype is exposed to 1-32 GeV electron, pion and muon beam at Fermilab meson test beamline in 2008-2009. As a result of the test, the prototype is proven to have good performance.

Development of a portable assembly-type cosmic-ray muon module for measuring the density structure of a column of magma

We have developed a portable assembly type cosmic-ray muon telescope system with power-effective real-time readings to monitor the internal structure of a volcano. Using this system, we have performed measurements at the Satsuma-Iojima volcano and studied the feasibility of using a continuous flux of cosmic-ray muons over the observation period. The system is based on the measurement of time-dependent muon absorption along different, nearly horizontal paths through a solid body. The rationale is that one can deduce the time-dependent changes in the density distribution of muon absorption in the interior of the object where an absorption variation, i.e., a density path variation, becomes an intensity variation since the muon energy spectrum is exponential or, expressed otherwise, it drops rapidly when the energy threshold increases. The muon telescope, which has a surface area of 1 m2, was installed at the observation point located 1.2 km from the summit crater of Satsuma-Iojima. Muon tracks within scintillator layers in the telescope were analyzed continuously by real-time three-dimensional image processing to measure the level of absorption along different ray paths through the summit crater region. A typical angular resolution of the muon detector of ±16 mrad corresponds to a spatial resolution of ±20 m at a distance of 1.2 km. Our results show the density structure determined in Satsuma-Iojima volcano, Japan, which is located above sea level. A density structure situated above sea level can be analyzed at a resolution that is significantly higher than is possible with conventional geophysical measurements.

Defects in Ce-doped LuAG and YAG scintillation layers grown by liquid phase epitaxy

The single crystalline Lu3Al5O12 (LuAG) and Y3Al5O12 (YAG) garnet layers doped by Ce3+ ions were grown by the liquid phase epitaxy from the flux. The effect of the flux composition, growth conditions, and substrate polishing on the layer morphology, creation of defects, and on optical and emission properties of layers was studied. The defects typical of the epitaxial growth are discussed.

X-Ray Image Detector Based on Light Guides and Scintillators

This paper reports on a study concerning the design of an X-ray detector that is suitable to analyze a small area with high spatial resolution. The indirect method of X-ray detection is used, i.e., the X-rays are first converted into visible light, which is then detected. In this design, an array of CsI:Tl scintillators, encapsulated by aluminum walls, is coupled with an array of CMOS photodetectors. This structure, patented and described theoretically by the authors in previous works, can be obtained using the SU-8 negative photoresist as a sacrificial layer. The experimental work consisted in the deposition of a scintillator layer, and an aluminum layer on the active area of a commercially available digital imaging sensor, thus supporting the developed detector design. X-ray imaging tests were performed using the PHILIPS X'Pert equipment. Promising results were obtained, featuring high resolution and detail.

A low-temperature proton detector for a neutron lifetime experiment

PENeLOPE is a new high-precision experiment with stored ultra-cold neutrons (UCN) to measure the neutron lifetime τ n planned at the Technische Universität München. A key element to reach the goal of 0.1 s precision is the in situ detection of the decay protons during storage. For this reason we plan to cover the top of the storage volume by a large-area scintillation counter working at cryogenic temperatures: a 1 μ m thin layer of CsI scintillator, evaporated on a light-guide structure and read from the side by large-area avalanche photo diodes (LAAPDs) will be used. Simulations showed that the layer thickness of 1 μ m is sufficient to stop the n-decay protons after additional post-acceleration by 40-keV from our PENeLOPE setup. A small scale test detector with a 1.5 μ m thick evaporated CsI layer was successfully operated at cryogenic temperatures in the range of 50 K. The produced scintillation light was measured from the side window of the light guide by an LAAPD from RMD. The signal-to-noise ratio of a 40-keV proton beam from the paff accelerator showed a signal-to-noise ratio of 17:1. Electron–proton separation was successfully demonstrated by shooting 40-keV protons and 15-keV electrons simultaneously onto the detector.