Thick Scintillator Research Articles

Multi-level radioisotope batteries based on 60Co γ source and Radio-voltaic/Radio-photovoltaic dual effects

A dual effect multi-level isotope battery based on γ radioisotope source was proposed. Two types of energy conversion mechanisms, namely, radio-voltaic (RV) and radio-photovoltaic (RPV) effects, was combined to convert the radiation energy of γ ray to electricity. The theoretical performance limit for the dual effect multi-level isotope battery irradiated by 60Co radioisotope source was calculated, and the characteristics of each conversion mechanism were analyzed by using MCNP5. The results revealed that the RPV effect produced more electrical output than the RV effect, but the contribution of each effect on the battery was significant. The output performance of the multi-level isotope battery was characterized under 60Co source at dose rates of 0.103 kGy/h and 0.68 kGy/h. The theoretical and experimental study investigated the feasibility of combining two kinds of energy conversion mechanisms to enhance the performance of nuclear batteries. The use of 60Co radioisotope sources with a large activity and conversion modules with additional levels could obtain a considerable output performance. Moreover, the thickness influence of the LYSO scintillator on the performance limit in the first-level conversion module was studied to optimize the structural parameters of the multi-level dual effect isotope battery. The thickness of scintillator strongly affects the energy deposition distribution of gamma rays in the multi-level conversion module, resulting in changes of the output generated by RV and RPV effects, which in turn affects the total output of the battery.

Scalable gamma-ray camera for wide-area search based on silicon photomultipliers array.

Portable coded-aperture imaging systems based on scintillators and semiconductors have found use in a variety of radiological applications. For stand-off detection of weakly emitting materials, large volume detectors can facilitate the rapid localization of emitting materials. We describe a scalable coded-aperture imaging system based on 5.02 × 5.02 cm2 CsI(Tl) scintillator modules, each partitioned into 4 × 4 × 20 mm3 pixels that are optically coupled to 12 × 12 pixel silicon photo-multiplier (SiPM) arrays. The 144 pixels per module are read-out with a resistor-based charge-division circuit that reduces the readout outputs from 144 to four signals per module, from which the interaction position and total deposited energy can be extracted. All 144 CsI(Tl) pixels are readily distinguishable with an average energy resolution, at 662 keV, of 13.7% FWHM, a peak-to-valley ratio of 8.2, and a peak-to-Compton ratio of 2.9. The detector module is composed of a SiPM array coupled with a 2 cm thick scintillator and modified uniformly redundant array mask. For the image reconstruction, cross correlation and maximum likelihood expectation maximization methods are used. The system shows a field of view of 45° and an angular resolution of 4.7° FWHM.

Modeling of proton-induced radioactivation background in hard X-ray telescopes: Geant4-based simulation and its demonstration by Hitomi’s measurement in a low Earth orbit

Hard X-ray astronomical observatories in orbit suffer from a significant amount of background due to radioactivation induced by cosmic-ray protons and/or geomagnetically trapped protons. Within the framework of a full Monte Carlo simulation, we present modeling of in-orbit instrumental background which is dominated by radioactivation. To reduce the computation time required by straightforward simulations of delayed emissions from activated isotopes, we insert a semi-analytical calculation that converts production probabilities of radioactive isotopes by interaction of the primary protons into decay rates at measurement time of all secondary isotopes. Therefore, our simulation method is separated into three steps: (1) simulation of isotope production, (2) semi-analytical conversion to decay rates, and (3) simulation of decays of the isotopes at measurement time. This method is verified by a simple setup that has a CdTe semiconductor detector, and shows a 100-fold improvement in efficiency over the straightforward simulation. To demonstrate its experimental performance, the simulation framework was tested against data measured with a CdTe sensor in the Hard X-ray Imager onboard the Hitomi X-ray Astronomy Satellite, which was put into a low Earth orbit with an altitude of 570 km and an inclination of 31°, and thus experienced a large amount of irradiation from geomagnetically trapped protons during its passages through the South Atlantic Anomaly. The simulation is able to treat full histories of the proton irradiation and multiple measurement windows. The simulation results agree very well with the measured data, showing that the measured background is well described by the combination of proton-induced radioactivation of the CdTe detector itself and thick Bi4Ge3O12 scintillator shields, leakage of cosmic X-ray background and albedo gamma-ray radiation, and emissions from naturally contaminated isotopes in the detector system.

Optimization of thickness of GAGG scintillator for detecting an alpha particle emitter in a field of high beta and gamma background

At the site of the Fukushima Daiichi nuclear power plant (FDNPP), there is a large quantity of beta and gamma emitters such as 90Sr and 137Cs. Moreover, radon (Rn) progeny, which are naturally occurring radionuclides, exist and emit alpha and beta particles. To detect plutonium isotopes (238Pu, 239Pu, and 240Pu) in a field of high beta and gamma background, an alpha particle detector with low beta- and gamma-ray sensitivity and good energy resolution for an alpha particle is required to distinguish plutonium isotopes from Rn progeny. Previously, we developed an alpha particle imaging detector by combining a 0.1-mm-thick gadolinium aluminum gallium garnet (GAGG) scintillator with a silicon photomultiplier (SiPM). However, this detector was sensitive to environmental gamma and beta rays. In this study, we optimized the thickness of the GAGG scintillator for alpha particle detection in a field of high beta and gamma background. We prepared three GAGG scintillators with thicknesses of 0.05 mm, 0.07 mm, and 0.1 mm. Each of the GAGG scintillators was coupled optically to the SiPM array, which was used as the photodetector. Alpha, beta, and gamma rays were irradiated onto the developed alpha particle detector, and their spectra were obtained. The energy resolution of the 0.05-mm-thick GAGG for 5.5-MeV alpha particles (∼11.6% full width at half maximum [FWHM]) was the best among the three GAGG scintillators. All GAGG scintillators used in this study were not sensitive to gamma rays with a dose rate of 1 mSv/h. The beta particle count above the lower level discriminator (LLD) decreased because the scintillator was thinner, and the beta count of the 0.05-mm-thick GAGG was only 1/100 that of the 0.1-mm-thick GAGG. Because the alpha particle detector with the 0.05-mm-thick GAGG scintillator had low beta and gamma-ray sensitivity and good energy resolution for alpha particles, it is promising from the viewpoint of detecting plutonium contamination in a field with high beta and gamma background, such as the FDNPP site.

800 fps neutron radiography of air-water two-phase flow

We have demonstrated dynamic cold neutron imaging of air-water two-phase flows up to 800 frames per second imaging rates. This has been achieved by using a high-efficiency (relatively thick) scintillator screen in combination with the highest available flux on a continuous spallation source and a high-speed sCMOS camera. This combination renders the spatial resolution to relatively modest value of about 0.5?mm, which is nevertheless sufficient for resolution of bubbles of the size down to about 1.0?mm in motion with unprecedented framerate using neutron imaging. We show the feasibility of the technique on the two-phase flow at ambient temperature and atmospheric pressure conditions, with the foreseen aim of measurements of two phase flows at high-temperatures and high pressures. It is also foreseen that the technique will be further utilized for quantification of the time-resolved instantaneous gas fraction and the gas phase velocity.•Demonstration of up to 800 frames per second dynamic cold neutron radiography.•Application of such technique for non-periodic (transient) process of bubbly flow in water.•Potential for quantification of (i) instantaneous gas volume fraction in dynamic two-phase flow and (ii) instantaneous gas phase velocimetry.

DEVELOPMENT OF A HIGH-EFFICIENCY PROTON RECOIL TELESCOPE FOR D-T NEUTRON FLUENCE MEASUREMENT.

A high-efficiency proton recoil telescope was developed to determine neutron fluences in neutron fields using the 3H(d,n)4He reaction. A 2-mm thick plastic scintillation detector was employed as a radiator to increase the detection efficiency and compensate for the energy loss of the recoil proton within. Two silicon detectors were employed as the ΔE and E detectors. The distance between the radiator and the E detector was varied between 50 and 150 mm. The telescope had detection efficiencies of 3.5 × 10-3 and 7.1 × 10-4 cm2 for distances of 50 and 100 mm, respectively, which were high enough to determine the neutron fluence in 14.8-MeV neutron fields, with a few thousand cm-2 s-1 fluence rate, within a few hours.

Performance of the Commercial PP/ZnS:Cu and PP/ZnS:Ag Scintillation Screens for Fast Neutron Imaging

Fast neutron imaging has a great potential as a nondestructive technique for testing large objects. The main factor limiting applications of this technique is detection technology, offering relatively poor spatial resolution of images and low detection efficiency, which results in very long exposure times. Therefore, research on development of scintillators for fast neutron imaging is of high importance. A comparison of the light output, gamma radiation sensitivity and spatial resolution of commercially available scintillator screens composed of PP/ZnS:Cu and PP/ZnS:Ag of different thicknesses are presented. The scintillators were provided by RC Tritec AG company and the test performed at the NECTAR facility located at the FRM II nuclear research reactor. It was shown that light output increases and the spatial resolution decreases with the scintillator thickness. Both compositions of the scintillating material provide similar light output, while the gamma sensitivity of PP/ZnS:Cu is significantly higher as compared to PP/ZnS:Ag-based scintillators. Moreover, we report which factors should be considered when choosing a scintillator and what are the limitations of the investigated types of scintillators.

Modeling and evaluation of a high-resolution CMOS detector for cone-beam CT of the extremities.

Quantitative assessment of trabecular bone microarchitecture in extremity cone-beam CT (CBCT) would benefit from the high spatial resolution, low electronic noise, and fast scan time provided by complementary metal-oxide semiconductor (CMOS) x-ray detectors. We investigate the performance of CMOS sensors in extremity CBCT, in particular with respect to potential advantages of thin (<0.7mm) scintillators offering higher spatial resolution. A cascaded systems model of a CMOS x-ray detector incorporating the effects of CsI:Tl scintillator thickness was developed. Simulation studies were performed using nominal extremity CBCT acquisition protocols (90kVp, 0.126mAs/projection). A range of scintillator thickness (0.35-0.75mm), pixel size (0.05-0.4mm), focal spot size (0.05-0.7mm), magnification (1.1-2.1), and dose (15-40mGy) was considered. The detectability index was evaluated for both CMOS and a-Si:H flat-panel detector (FPD) configurations for a range of imaging tasks emphasizing spatial frequencies associated with feature size aobj. Experimental validation was performed on a CBCT test bench in the geometry of a compact orthopedic CBCT system (SAD=43.1cm, SDD=56.0cm, matching that of the Carestream OnSight 3D system). The test-bench studies involved a 0.3mm focal spot x-ray source and two CMOS detectors (Dalsa Xineos-3030HR, 0.099mm pixel pitch) - one with the standard CsI:Tl thickness of 0.7mm (C700) and one with a custom 0.4mm thick scintillator (C400). Measurements of modulation transfer function (MTF), detective quantum efficiency (DQE), and CBCT scans of a cadaveric knee (15mGy) were obtained for each detector. Optimal detectability for high-frequency tasks (feature size of ~0.06mm, consistent with the size of trabeculae) was ~4× for the C700 CMOS detector compared to the a-Si:H FPD at nominal system geometry of extremity CBCT. This is due to ~5× lower electronic noise of a CMOS sensor, which enables input quantum-limited imaging at smaller pixel size. Optimal pixel size for high-frequency tasks was <0.1mm for a CMOS, compared to ~0.14mm for an a-Si:H FPD. For this fine pixel pitch, detectability of fine features could be improved by using a thinner scintillator to reduce light spread blur. A 22% increase in detectability of 0.06mm features was found for the C400 configuration compared to C700. An improvement in the frequency at 50% modulation (f50 ) of MTF was measured, increasing from 1.8lp/mm for C700 to 2.5lp/mm for C400. The C400 configuration also achieved equivalent or better DQE as C700 for frequencies above ~2mm-1 . Images of cadaver specimens confirmed improved visualization of trabeculae with the C400 sensor. The small pixel size of CMOS detectors yields improved performance in high-resolution extremity CBCT compared to a-Si:H FPDs, particularly when coupled with a custom 0.4mm thick scintillator. The results indicate that adoption of a CMOS detector in extremity CBCT can benefit applications in quantitative imaging of trabecular microstructure in humans.

A novel method for quantification of beam's-eye-view tumor tracking performance.

In-treatment imaging using an electronic portal imaging device (EPID) can be used to confirm patient and tumor positioning. Real-time tumor tracking performance using current digital megavolt (MV) imagers is hindered by poor image quality. Novel EPID designs may help to improve quantum noise response, while also preserving the high spatial resolution of the current clinical detector. Recently investigated EPID design improvements include but are not limited to multi-layer imager (MLI) architecture, thick crystalline and amorphous scintillators, and phosphor pixilation and focusing. The goal of the present study was to provide a method of quantitating improvement in tracking performance as well as to reveal the physical underpinnings of detector design that impact tracking quality. The study employs a generalizable ideal observer methodology for the quantification of tumor tracking performance. The analysis is applied to study both the effect of increasing scintillator thickness on a standard, single-layer imager (SLI) design as well as the effect of MLI architecture on tracking performance. The present study uses the ideal observer signal-to-noise ratio (d') as a surrogate for tracking performance. We employ functions which model clinically relevant tasks and generalized frequency-domain imaging metrics to connect image quality with tumor tracking. A detection task for relevant Cartesian shapes (i.e., spheres and cylinders) was used to quantitate trackability of cases employing fiducial markers. Automated lung tumor tracking algorithms often leverage the differences in benign and malignant lung tissue textures. These types of algorithms (e.g., soft-tissue localization - STiL) were simulated by designing a discrimination task, which quantifies the differentiation of tissue textures, measured experimentally and fit as a power-law in trend (with exponent β) using a cohort of MV images of patient lungs. The modeled MTF and NPS were used to investigate the effect of scintillator thickness and MLI architecture on tumor tracking performance. Quantification of MV images of lung tissue as an inverse power-law with respect to frequency yields exponent values of β=3.11 and 3.29 for benign and malignant tissues, respectively. Tracking performance with and without fiducials was found to be generally limited by quantum noise, a factor dominated by quantum detective efficiency (QDE). For generic SLI construction, increasing the scintillator thickness (gadolinium oxysulfide - GOS) from a standard 290μm to 1720μm reduces noise to about 10%. However, 81% of this reduction is appreciated between 290 and 1000μm. In comparing MLI and SLI detectors of equivalent individual GOS layer thickness, the improvement in noise is equal to the number of layers in the detector (i.e., 4) with almost no difference in MTF. Further, improvement in tracking performance was slightly less than the square-root of the reduction in noise, approximately 84-90%. In comparing an MLI detector with an SLI with a GOS scintillator of equivalent total thickness, improvement in object detectability is approximately 34-39%. We have presented a novel method for quantification of tumor tracking quality and have applied this model to evaluate the performance of SLI and MLI EPID designs. We showed that improved tracking quality is primarily limited by improvements in NPS. When compared to very thick scintillator SLI, employing MLI architecture exhibits the same gains in QDE, but by mitigating the effect of optical Swank noise, results in more dramatic improvements in tracking performance.

Removal of ring artifacts in microtomography by characterization of scintillator variations.

Ring artifacts reduce image quality in tomography, and arise from faulty detector calibration. In microtomography, we have identified that ring artifacts can arise due to high-spatial frequency variations in the scintillator thickness. Such variations are normally removed by a flat-field correction. However, as the spectrum changes, e.g. due to beam hardening, the detector response varies non-uniformly introducing ring artifacts that persist after flat-field correction. In this paper, we present a method to correct for ring artifacts from variations in scintillator thickness by using a simple method to characterize the local scintillator response. The method addresses the actual physical cause of the ring artifacts, in contrary to many other ring artifact removal methods which rely only on image post-processing. By applying the technique to an experimental phantom tomography, we show that ring artifacts are strongly reduced compared to only making a flat-field correction.

Characterizing and simulation the scintillation properties of zinc oxide nanowires in AAO membrane for medical imaging applications

In this work, a new method is proposed for extracting some X-ray detection properties of ZnO nanowires electrodeposited on Anodized Aluminum Oxide (AAO) nanoporous template. The results show that the detection efficiency for 12μm thickness of zinc oxide nano scintillator at an energy of 9.8 keV, near the K-edge of ZnO (9.65 keV), is 24%. The X-rays that interact with AAO can also generate electrons that reach the nano scintillator. The scintillation events of these electrons are seen as a low energy tail in the spectrum. In addition, it is found that all the X-rays that are absorbed in 300 nm thickness of the gold layer on the top of the zinc oxide nanowires can participate in the scintillation process with an efficiency of 6%. Hence, the scintillation detection efficiency of the whole detector for 9.8 keV X-ray energy is 30%. The simulation results from Geant4 and the experimental detected photons per MeV energy deposition are also used to extract the light yield of the zinc oxide nano scintillator. The results show that the light yield of the zinc oxide nanowires deposited by the electrochemical method is approximately the same as for single crystal zinc oxide scintillator (9000). Much better spatial resolution of this nano scintillator in comparison to the bulk ones is an advantage which candidates this nano scintillator for medical imaging applications.

Multisector scintillation detector with fiber-optic light collection

A new type of scintillation detector for the use in high energy physics is described. The octagonal detector consists of eight triangular scintillator sectors with total area of 1 m2. Each sector represents two plates of 2 cm thick plastic scintillator. Seven 1 mm thick WLS fibers are laid evenly between the plates. The space between the fibers is filled with silicone compound to provide better light collection. Fiber ends from all eight sectors are gathered in the central part of the detector into a bunch and docked to the cathode of a FEU-115m photomultiplier. The read-out of the counter signals is carried out from 7th and 12th dynodes, providing a wide dynamic range up to about 10000 particles. The front-end electronics of the detector is based on the flash-ADC with a sampling frequency of 200 MHz. The features of detecting and recording systems of the multisector scintillation detector (MSD) and the results of its testing are discussed.

Performance Study of a Large Monolithic LYSO PET Detector With Accurate Photon DOI Using Retroreflector Layers

Clinical and organ-dedicated PET systems typically require a high efficiency imposing the use of thick scintillators, normally through crystal arrays. To provide depth of interaction (DOI) information, two or more layers are sometimes mounted in the staggered or phoswich approach. In this paper, we are proposing an alternative using thick and large monolithic crystals. We have tested two surface treatments for a 50 mm $\times50$ mm $\times20$ mm LYSO block. We provide data in this paper as close as 5 mm to the lateral walls. We left those walls black painted and the exit face coupled to the photosensor ( $12\times12$ SiPM array) polished. The entrance face was: 1) black painted or 2) coupled to a retroreflector (RR) layer. These configurations keep a good DOI linearity and, on average, reached 4 mm DOI resolution, measured as the full width at half of the maximum. Approaches using RR layers return constant and good energy resolutions nearing 12%, compared to a range of 15%–16% in the case of totally black painted blocks. The best result concerning the detector spatial resolution was obtained when one of the smallest RR was used (120 $\mu {\mathrm{ m}}$ corner cube size), being 1.7 mm at the entrance crystal layer and 0.7 mm in the layer closest to the photosensor. These values worsen at least 30% for the black treatment case.

Estimation of optimum scintillator thickness of Si-PM detectors for time-of-flight (TOF)-PET

Time-of-flight (TOF) is an effective method for improving signal-to-noise ratio of the images for PET. Basic performance of TOF-PET such as sensitivity, TOF-gain, and energy resolution depends on the scintillator thickness. Hence, determining the appropriate scintillator thickness is crucial when designing TOF-PET systems. However, the optimal thickness for the Lu-based scintillators is often not clear-cut. In this paper, we introduce a new concept (figure of merit, FOM) to evaluate the optimum scintillator thickness with regards to the above factors for a TOF-PET system employing Lu-based scintillators coupled to silicon photomultipliers (Si-PMs). We optically coupled Lu1.9Gd0.1SiO5 (LGSO) scintillators of different thickness (length) to Si-PMs and measured the timing resolutions with a high bandwidth digital oscilloscope. Then we calculated the TOF-gain for each crystal. We also calculated the coincidence detection efficiencies. Finally, for each LGSO length, we evaluated the relative sensitivity with FOMs that take into account the TOF-gain (TOF-sensitivity). From this study, we found that LGSO with 20–25 mm thickness was optimum based on the calculated TOF-sensitivity FOM. We conclude that the evaluation methods and results can provide an objective method in which one may use to determine the optimum thickness of the scintillators for TOF-PET systems.

High-resolution extremity cone-beam CT with a CMOS detector: Task-based optimization of scintillator thickness.

CMOS x-ray detectors offer small pixel sizes and low electronic noise that may support the development of novel high-resolution imaging applications of cone-beam CT (CBCT). We investigate the effects of CsI scintillator thickness on the performance of CMOS detectors in high resolution imaging tasks, in particular in quantitative imaging of bone microstructure in extremity CBCT. A scintillator thickness-dependent cascaded systems model of CMOS x-ray detectors was developed. Detectability in low-, high- and ultra-high resolution imaging tasks (Gaussian with FWHM of ~250 μm, ~80 μm and ~40 μm, respectively) was studied as a function of scintillator thickness using the theoretical model. Experimental studies were performed on a CBCT test bench equipped with DALSA Xineos3030 CMOS detectors (99 μm pixels) with CsI scintillator thicknesses of 400 μm and 700 μm, and a 0.3 FS compact rotating anode x-ray source. The evaluation involved a radiographic resolution gauge (0.6-5.0 lp/mm), a 127 μm tungsten wire for assessment of 3D resolution, a contrast phantom with tissue-mimicking inserts, and an excised fragment of human tibia for visual assessment of fine trabecular detail. Experimental studies show ~35% improvement in the frequency of 50% MTF modulation when using the 400 μm scintillator compared to the standard nominal CsI thickness of 700 μm. Even though the high-frequency DQE of the two detectors is comparable, theoretical studies show a 14% to 28% increase in detectability index (d'2) of high- and ultrahigh resolution tasks, respectively, for the detector with 400 μm CsI compared to 700 μm CsI. Experiments confirm the theoretical findings, showing improvements with the adoption of 400 μm panel in the visibility of the radiographic pattern (2× improvement in peak-to-through distance at 4.6 lp/mm) and a 12.5% decrease in the FWHM of the tungsten wire. Reconstructions of the tibial plateau reveal enhanced visibility of trabecular structures with the CMOS detector with 400 μm scinitllator. Applications on CMOS detectors in high resolution CBCT imaging of trabecular bone will benefit from using a thinner scintillator than the current standard in general radiography. The results support the translation of the CMOS sensor with 400 μm CsI onto the clinical prototype of CMOS-based extremity CBCT.

A CMOS-based high resolution fluoroscope (HRF) detector prototype with 49.5 μm pixels for use in endovascular image guided interventions (EIGI).

X-ray detectors to meet the high-resolution requirements for endovascular image-guided interventions (EIGIs) are being developed and evaluated. A new 49.5-micron pixel prototype detector is being investigated and compared to the current suite of high-resolution fluoroscopic (HRF) detectors. This detector featuring a 300-micron thick CsI(Tl) scintillator, and low electronic noise CMOS readout is designated the HRF-CMOS50. To compare the abilities of this detector with other existing high resolution detectors, a standard performance metric analysis was applied, including the determination of the modulation transfer function (MTF), noise power spectra (NPS), noise equivalent quanta (NEQ), and detective quantum efficiency (DQE) for a range of energies and exposure levels. The advantage of the smaller pixel size and reduced blurring due to the thin phosphor was exemplified when the MTF of the HRF-CMOS50 was compared to the other high resolution detectors, which utilize larger pixels, other optical designs or thicker scintillators. However, the thinner scintillator has the disadvantage of a lower quantum detective efficiency (QDE) for higher diagnostic x-ray energies. The performance of the detector as part of an imaging chain was examined by employing the generalized metrics GMTF, GNEQ, and GDQE, taking standard focal spot size and clinical imaging parameters into consideration. As expected, the disparaging effects of focal spot unsharpness, exacerbated by increasing magnification, degraded the higher-frequency performance of the HRF-CMOS50, while increasing scatter fraction diminished low-frequency performance. Nevertheless, the HRF-CMOS50 brings improved resolution capabilities for EIGIs, but would require increased sensitivity and dynamic range for future clinical application.

Development of shashlik electromagnetic calorimeter prototype for SoLID

A shashlik electromagnetic calorimeter will be produced in Hall A of Jefferson Laboratory for Solenoidal large Intensity Device (SoLID) to measure the energy deposition of electrons and hadrons, and to provide particle identification after the energy of the accelerator was upgraded to 12 GeV. Tsinghua University is the member of Hall A collaboration in charge of development and production of the large shashlik electromagnetic calorimeter of SoLID. One module of that calorimeter is composed by 194 layers. Each layer consists of a 1.5 mm thick plastic scintillator put on top of a 0.5 mm thick lead plate. Scintillation light is read out by wave-length shifter fibers penetrating through the calorimeter modules longitudinally along the direction of flight of the impact particle. This paper describes the design and construction of that module, as well as a few optimization studies meant to improve its performance. A detailed Geant4 simulation also shows that an energy resolution of 5%/√ E (GeV) and a good containment for electromagnetic showers can be achieved, as well as some basic electron identification. A prototype of that module will be tested soon with an electron beam at JLab.

Deriving depth-dependent light escape efficiency and optical Swank factor from measured pulse height spectra of scintillators.

Pulse height spectroscopy has been used by investigators to deduce the imaging properties of scintillators. Pulse height spectra (PHS) are used to compute the Swank factor, which describes the variation in scintillator light output per x-ray interaction. The spread in PHS measured below the K-edge is related to the optical component of the Swank factor, i.e., variations in light escape efficiency from different depths of x-ray interaction in the scintillator, denoted ε¯(z). Optimizing scintillators for medical imaging applications requires understanding of these optical properties, as they determine tradeoffs between parameters such as x-ray absorption, light yield, and spatial resolution. This work develops a model for PHS acquisition such that the effect of measurement uncertainty can be removed. This method allows ε¯(z) to be quantified on an absolute scale and permits more accurate estimation of the optical Swank factor of scintillators. The pulse height spectroscopy acquisition chain was modeled as a linear system of stochastic gain stages. Analytical expressions were derived for signal and noise propagation through the PHS chain, accounting for deterministic and stochastic aspects of x-ray absorption, scintillation, and light detection with a photomultiplier tube. The derived expressions were used to calculate PHS of thallium-doped cesium iodide (CsI) scintillators using parameters that were measured, calculated, or known from literature. PHS were measured at 25 and 32 keV of CsI samples designed with an optically reflective or absorptive backing, with or without a fiber-optic faceplate (FOP), and with thicknesses ranging from 150-1000 μm. Measured PHS were compared with calculated PHS, then light escape model parameters were varied until measured and modeled results reached agreement. Resulting estimates of ε¯(z) were used to calculate each scintillator's optical Swank factor. For scintillators of the same optical design, only minor differences in light escape efficiency were observed between samples with different thickness. As thickness increased, escape efficiency decreased by up to 20% for interactions furthest away from light collection. Optical design (i.e., backing and FOP) predominantly affected the magnitude and relative variation in ε¯(z). Depending on interaction depth and scintillator thickness, samples with an absorptive backing and FOP were estimated to yield 4.1-13.4 photons/keV. Samples with a reflective backing and FOP yielded 10.4-18.4 keV-1 , while those with a reflective backing and no FOP yielded 29.5-52.0 keV-1 . Optical Swank factors were approximately 0.9 and near-unity in samples featuring an absorptive or reflective backing, respectively. This work uses a modeling approach to remove the noise introduced by the measurement apparatus from measured PHS. This method allows absolute quantification of ε¯(z) and more accurate estimation of the optical Swank factor of scintillators. The method was applied to CsI scintillators with different thickness and optical design, and determined that optical design more strongly affects ε¯(z) and Swank factor than differences in CsI thickness. Despite large variations in ε¯(z) between optical designs, the Swank factor of all evaluated samples is above 0.9. Information provided by this methodology can help validate Monte Carlo simulations of structured CsI and optimize scintillator design for x-ray imaging applications.

Gamma Spectroscopy: High Resolution CAM for Imaging in Nuclear Physics

In Nuclear science essential research and, especially, in gamma spectroscopy, the utilization of an imaging pioneer can be to an exceptional degree steady to reduce the Doppler Broadening influence in examinations where the gamma-bar source moves with high speed. In this work, we propose to utilize a beginning at starting late made gamma camera, in context of scintillator coupled to an arrangement of Silicon Drift Detectors, for such kind of tests. The camera, fittingly changed as per conform to high noteworthiness territory, has appeared, in preparatory estimations with a one cm thick scintillator, a spatial confirmation of two millimetre with a collimated source.

Discrimination of charged particles in a neutral beam line by using a solid scintillation detector

In the past several decades, many studies have been conducted to search for non-baryonic dark matter, such as weakly interactive massive particles (WIMPs). In the search for WIMPs, charged particles incident on the detector are background particles because WIMPs are neutral. Charged particles originate from various sources, such as cosmic rays and laboratory materials surrounding the main detector. Therefore, a veto that discriminates charged particles can improve the particle-detection efficiency of the entire experiment for detecting WIMPs. Here, we investigate in the thickness range of 1 mm to 5 mm, the optimal thickness of a polystyrene scintillator as a chargedparticle veto detector. We found that 3-mm-thick polystyrene provides the best performance to veto charged particles and the charged-particle background in the search for the WIMP signal. Furthermore, we fabricated 3-mm-thick and 5-mm-thick polystyrene charged particle veto detectors that will be used in an underground laboratory in the search for WIMP dark matter. After exposing those detectors are the actual beam line, we compared the rate of charged particles measured using those detectors and the rate simulated through a Monte Carlo simulation.