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Development of a Transmission-type Ultra-thin ScCVD Diamond Detector for Alpha Particles (#8)
X. Cheng1, S. H. Byun2, 1
1 McMaster University, Radiation Sciences Graduate Program, Hamilton, Ontario, Canada
We present an ultra-thin transmission-type radiation detector fabricated from optical grade ([N]<1 ppm) single crystal chemical vapor deposited (ScCVD) diamond for microbeam alpha particles detection. The commercially available ScCVD diamond samples (3 mm × 3 mm × 50µm) was plasma etched down to a few µm thickness which allows alpha particles to penetrate, and then it was followed by the surface treatments for electrical contact. In order to evaluate the performance of the ultra-thin ScCVD diamond detector, a ΔE-E detection system was setup using a calibration alpha source, the ScCVD diamond detector and a silicon barrier detector. Promised counting performance and transmission ability of alpha particles was observed and verified.
Keywords: CVD diamond, alpha particles, semiconductor
An Associated Particle Imaging System for 3D Elemental Measurements (#10)
M. Ayllon Unzueta1, 5, B. Ludewigt1, B. Mak1, C. Castanha2, E. Brodie2, C. Hicks Pries4, C. Gary3, C. Brown3, A. Persaud1
1 Lawrence Berkeley National Laboratory, Accelerator Technology & Applied Physics, Berkeley, California, United States of America
The ability to create 3D images and obtain elemental information from unknown/hidden objects makes Associated Particle Imaging (API) a valuable technique for homeland security and nuclear safeguards applications. High-energy neutrons (14 MeV) produced by deuterium-tritium fusion reactions in a compact neutron generator can interact with an unknown sample via inelastic scattering. Measuring the resulting gamma rays in coincidence with the associated alpha particles allows for both a 3D reconstruction of the object and detailed analysis of its isotopic composition. Other approaches using the API technique involve, for example, neutron transmission and induced-fission imaging.
At Lawrence Berkeley National Laboratory, we designed and built an API system to measure elemental distributions in soil, however, the technical advancements presented in this work apply equally well to other API applications. The most relevant components of the API system include an alpha detector system (used to tag the 14 MeV neutrons), which consists of a Yttrium Aluminum Perovskite (YAP, activated by Ce3+) scintillator, a sapphire vacuum window, and a Hamamatsu (H13700-03) photo-mupltiplier tube. Additionally, we employ an Adelphi DT108API neutron generator equipped with this novel alpha detector. A second API generator has been built and it incorporates several improvements important for API measurements, including reduced neutron and alpha particle scattering and lower X-ray background in the alpha detector, as well as other improvements on the overall performance. In our API system, a 3” × 3” LaBr3 and a 5” × 5” NaI detector are used for gamma detection and the data acquisition is handled by an all-digital Pixie-16 from XIA, Inc. Using these components we achieved an excellent position resolution at the target location (~50 cm from the neutron source) of 4 cm in the lateral dimension (X,Y), enabled by a small neutron spot size of ~2 mm in diameter and an alpha detector position resolution of <0.5 mm. We also achieved a 7 cm depth resolution with the LaBr detector, which was enabled by a system time resolution of ~1 ns.
We will present details of our instrument and results from resolution measurements. Additionally, we will show 3D-reconstructed images from samples consisting of different materials and discuss future improvements to the system to achieve higher rate-handling capabilities and better depth resolution.
Keywords: neutron, imaging, associated particle imaging
Boron-Loaded Deuterated Liquid Scintillator Response Characterization (#11)
B. V. Egner1, J. E. Bevins1, M. Febbraro2
1 The Air Force Institute of Technology, Department Of Engineering Physics, Wright-Patterson AFB, Ohio, United States of America
The detector response for a boron-loaded deuterated liquid scintillator (BLDLS) is characterized for future neutron spectrum unfolding measurements and compared to both an un-loaded deuterated liquid scintillator and a commercially available hydrogen-based scintillator, EJ-309. This research serves to present the characterization methods and results for determining the pulse integral spectrum response calibration, resolution, efficiency, and heavy charged particle light yield functions through a combination of experimental neutron and gamma-ray measurements coupled with Monte Carlo radiation transport simulations in Geant4. Neutron time-of-flight measurements of a 252Cf source using each scintillator are currently being performed to generate quasi-mono-energetic neutron responses to serve as inputs for a recoil particle light yield Monte Carlo feedback loop to estimate the light yield parameters for the KamLAND model, a modified version of Birks' model. Additionally, a 10B neutron capture gamma-ray coincident measurement will be used to estimate the BLDLS alpha-particle light yield induced by 10B(n,α)7Li* reaction. Finally, full detector response matrices, used for spectrum unfolding, will be generated for each scintillator, and the condition of the response matrices will be evaluated. Current results show the BLDLS has a high sensitivity and separable response for thermal neutrons without significantly quenching the scintillator light yield compared to the un-loaded baseline deuterated scintillator, a desirable capability for applications characterizing neutron sources where the level of shielding or moderating is unknown.
Keywords: Deuterated Scintillators, Neutron Spectroscopy, Neutron Detection
Nanoscale Light Transport Characterization using Geant4 (#16)
S. Surani1, P. Albert2, P. Lauer2, D. Wolfe2, M. Flaska1
1 Pennsylvania State University, Nuclear Engineering, State College, Pennsylvania, United States of America
Inorganic scintillators are some of the most utilized and versatile options for gamma-ray or neutron detection. These scintillators typically have a high light yield, which allows them to have a relatively high energy resolution. However, a relatively large fraction of the light yield is trapped inside the scintillator because of the process called the total internal reflection. This occurs due to the high refractive index of most inorganic scintillators. It has been theorized that adding a photonic crystal layer between the scintillator and the light sensor will help increase the light output by reducing the fraction lost to the internal reflection. Photonic crystals are nanostructures whose thickness is typically in the range of the wavelength of visible light and whose refractive index is higher than that of the scintillator. The higher refractive index reduces the internal reflection, while the photonic crystal structure increases light scattering. These combined effects improve the light extraction from the scintillator, thereby improving the scintillator’s energy resolution.
Accurate nanoscale light transport simulations are required to model such photonic crystals. However, many light transport codes cannot accurately simulate the complexities that arise at a nanoscale level. The Geant4 code uses optical photons as particles for the light transport, thus providing a completely stochastic tool for nanoscale light simulations. In this research, we investigate and assess the performance of the Geant4 code for such nanoscale simulations. Specifically, thin films made of TiO2 are characterized in UV-Vis optical experiments. The data obtained from the UV-Vis experiments are then used to model these films in Geant4. A mono-directional and mono-energetic light source with a range between 400 and 1000 nm is simulated in Geant4 to impinge on each TiO2 film. The simulated light transmission is compared with the light transmission obtained from the UV-Vis experiments. The simulation/measurement comparisons are performed for TiO2 films 87 and 600 nm thick, a TiO2 polycrystalline sample 500 um thick, and a TiO2 single crystal sample 1 mm thick.
The aforementioned characterization of the Geant4 nanoscale simulations is paramount for developing reliable and accurate photonic crystal simulations in Geant4. The resulting models can then be used to find an optimized geometry for the photonic crystals to improve light output for any existing or new-generation inorganic scintillator.
Keywords: Photonic Crystals, Nanoscale Light Transport, Geant4
Bi-modal imaging based on an e-LINAC driven photoneutron source (#24)
Y. Yu1, 2, Y. Yang1, 2
1 Tsinghua, Department of Engineering Physics, Beijing, China
X-ray imaging plays an irreplaceable role in the non-destructive inspection area for its good balance between the penetrating ability and analyzing sensitivity. For the MV X-rays, as Compton scattering is the dominating photo atomic reaction, only the mass thickness information of the inspected object can be acquired, and it is impossible to identify different objects of the same mass thickness that may cause the same attenuation to the X-rays. The dual-energy X-ray imaging, which fuses the images of X-rays of two different energies, enables the identification of objects with a varied atomic number. However, it can hardly effectively separate objects whose atomic numbers are next to each other, suffering from the smooth relationship between the photo atomic cross section and the atomic number. A Combination of the X-ray and neutron based imaging is a straightforward idea to enhance the capability of identifying objects because neutrons show a very different relationship between the cross section and atomic number. A typical way to realize this is introducing two different radiation sources into one system, one is reactor or accelerator based neutron source, and the other is an X-ray tube. In this paper, we present a new method that may incorporate both photons and neutrons within one e-LINAC driven system. By selecting the different emitting angles of bremsstrahlung, X-rays with different energy spectra can be provided simultaneously. By placing a photon-to-neutron convertor next to the electron-to-photon convertor, photoneutrons can be delivered as the byproduct of X-ray pulses. The fusion of attenuation information of three radiations, high energy and low energy X-rays along the 0 degree and 90 degree emitting angles, respectively, as well as the photoneutrons, can significantly enhance the capability of materials identification.
Keywords: bi-modal imaging, neutron imaging, x-ray imaging
An Environmentally-Friendly Quantum Dot Gel-Based Thermal Neutron Detector (#26)
P. Ghosh1, C. Riddle2, D. Scates2, R. Fronk2
1 Kansas State University, Mechanical and Nuclear Engineering, Manhattan, Kansas, United States of America
The development of new neutron detectors to replace 3He detectors has become necessary due to a worldwide shortage of 3He. The “Scintillation Hydro-Gel for Isotopic Neutron Emitters”, or SHINE, is a first-of-its-kind, quantum dot-based gelatinous scintillator for thermal-neutron detection, developed at Idaho National Laboratory. SHINE, being in gel format, incorporates benefits of both solid and liquid scintillators while avoiding their respective disadvantages, such as those of liquid scintillators, like continuous filtering of contaminates, slow throughput of containers, higher base component costs, and those of solid scintillators such as ‘dead’ voids in solid scintillators. SHINE also enables high loading of neutron-reactive material without compromising on light transparency. SHINE constitutes a gel base, a neutron converting material, and a scintillator. 6Li was chosen as the neutron converter, owing to its large thermal neutron cross-section. The alpha particle and triton emitted from the reaction between 6Li and neutron can deposit energy in a scintillator, leading to the emission of visible photons. Quantum dots (QDs) were selected over regular scintillator crystals; the former can be superior to their micro-sized counterparts because they are wavelength-tunable and have higher light yield due to greater surface area. QD core/shell structures have a semiconductor core such as InP, and is passivated by a shell of a wider bandgap semiconductor such as ZnS, used to improve the light yield of the QD. Enriched 6LiCl was used as the neutron converting material due to its high solubility in water, thereby enabling large loadings. Previously, Cd-based QD’s have been used as scintillators, however, Cd is environmentally toxic. Therefore, SHINE uses InP/ZnS, an eco-friendly QD with a large Stokes shift to prevent self-absorption of light. SHINE fabrication is a simple, two-step process that does not require any specialized laboratory equipment. A monomer is polymerized into gel form using a crosslinking agent, containing a high loading of 6LiCl, and QDs. Different loadings of 6LiCl and QD were tested for optimized neutron detection and photon collection, and a spectrophotometer was used to measure the gel’s transmittance. The gel was optically coupled to a photomultiplier tube and irradiated with moderated 252Cf to analyze the neutron detection performance. The detector was also irradiated with 137Cs to study the gamma-ray response. To distinguish background and gamma-ray event counts from neutron event counts, pulse shape analysis was performed. Counts that were attributable to neutron events were observed in the SHINE gel, as well as those attributed to cosmic muons interacting with the water in the gel, further indicating the requirement for pulse shape discrimination. SHINE has been successfully tested for neutron detection and demonstrates promise as both a replacement for current 3He neutron detectors as well as potential use in hand-held, compact neutron detection units and antineutrino detection.
Keywords: quantum dots, neutron scintillator, gel scintillator
ABALONE Photosensor PanelsTM for Large-Area Radiation Detection (#28)
I. Ferenc Segedin1, M. Segedin Ferenc1, D. Ferenc1, 2
1 PhotonLab, Inc., Fairfield, California, United States of America
The ABALONETM Photosensor Technology (U.S. Pat. 9,064,678) is a modern, scalable technology specifically invented for cost-effective mass production, robustness, and high performance. The performance makes a significant difference: wide dynamic range with gain up to109, total afterpulsing rate of only 5x10-3 ions per photoelectron, sub-nanosecond timing resolution, single-photon sensitivity, and unique radio-purity and UV sensitivity thanks to the fused silica components—at no additional cost to the assembly process. These unique features are further accompanied by simple, application-specific, cost-effective integration methods, such as a Tandem detector module (U.S. Pat. 9,064,678) that hosts two ABALONE units oriented in opposite directions, or, quite differently, a thin, lightweight, self-supporting and modular composite Panels (US-2017-0123084-A1) hosting closely packed matrices of ABALONE units, which are the subject of this presentation. We will present the results of extensive tests of ABALONE Photosensor Panels, and their comparison to numerical simulations. Following the proof of concept, PHOTONLAB, INC. is now focusing on the development and commercialization of the next generation of large-area radiation monitors and scanners based on the ABALONE Photosensor PanelsTM.
Keywords: photosensor, radiation detection, light detection
Depth of Interaction(DOI) Analysis Method based on Light Sharing and Artificial Neural Network (#37)
K. Ko1, W. Kim1, H. Choi1, J. Kim1, E. Ko1, G. Cho1
1 KAIST, Nuclear and Quantum Engineering, Daejeon, Republic of Korea
There are two main approaches to improve the sensitivity of PET. The first is to reduce the diameter of the PET scanner to bring the detector closer to the radiation source, and the second is to thicken the scintillator to increase the detection efficiency of gamma rays occurred by positron annihilation. However, in both cases, the spatial resolution will deteriorate as parallax error increases. The parallax error is a phenomenon in which annihilation gamma-ray penetrates the scintillator and other nearby elements detect the gamma-ray, leading to incorrect placement of the line of response (LOR), leading to a decrease in spatial resolution. The determination depth of interaction (DOI) can attenuate a decrease in spatial resolution due to parallax error.
1. Detector module
An optical rubber was inserted into a one-to-one coupling detector module to create an artificial gap. Through this space, the spread of optical photons generated by interaction with radiation and scintillator occurred. To minimize the attenuation of optical photons in the process, a scintillator with fully-polished surfaces was used, and ESR films with a reflectivity of 99% were used as reflectors.
To acquire the DOI information, we have to design an experiment that identifies the specific position in which radiation interacted. To do so, we used electronic and physical collimators.
ANN is used for decoding the difference in the degree of spread and intensity according to interaction depth. Each data consists of 64 ch with QDC value, indicating u,v position information (at u,v,w coordinate) and intensity of optical photon. In this work, the ANN structure was optimized with a random search method and evaluating the performance by dividing the original data set into Training, Validation, and Testing.
Result & Discussion
Case 1 and Case 2 refer to two and three DOI, respectively. Each case experimented with more than 100 events on 64 channels (e.g. Input # of case 2: 64 ch x 3 heights x 100 events). 'Total' in Table 1 represents the results of the evaluation of all 64 units, and 'Single' represents the results of the evaluation in different u and v positions. Case 1 showed more than 80% of test accuracy, and case 2 showed more than 60% of test accuracy. In addition, the result of the single shows that the test accuracy decreases slightly as u,v coordinate moves away from the center.
In this study, we confirmed that it is possible to identify the DOI information by the proposed method. However, the accuracy of DOI classification is decreased as the level of DOI more subdivided. To address this, it is considered that modifications in modules, etc are needed to clarify the differences according to the interaction depth. Furthermore, perfect elimination of parallax error also requires research for continuous DOI information acquisition beyond Discrete DOI identification.
Keywords: Depth of Interaction, artificial neural network, parallax error
Scalable, controllable inverse-temperature crystallization solution growth of monocrystalline organic-inorganic hybrid perovskites for direct gamma-ray spectroscopy. (#57)
S. Joglekar2, 1, M. Hammig2, L. J. Guo1
1 University of Michigan, Electrical Engineering and Computer Science Dept., Ann Arbor, Michigan, United States of America
High-resolution spectroscopic detection of gamma-rays is a vital technology for safeguarding special nuclear materials (SNM), and is also critical to other applications ranging from security to medical imaging and industrial non-destructive testing (NDT). However, commercial adoption of spectroscopic gamma-ray detectors and imagers is limited due to the tradeoff in the resolution performance versus system cost. While considerable improvements in the performance and portability of detection systems have been made in the past few decades, they are still too expensive for many non-security and non-medical commercial applications.
Recently, organic-inorganic hybrid perovskite (OIHP) materials have emerged, demonstrating the ability to grow high-quality, low-defect semiconductor materials using solution processing. Notably, OIHP-based photovoltaic (PV) devices nearly match the performance of silicon solar cells. Solution-processing methods were also used to grow mesoscopic OIHP perovskite single crystals (PSCs), with a length > 5 cm, using inverse-temperature crystallization (ITC). The use of ITC-grown PSCs as semiconductor gamma-ray detectors was first demonstrated by Kovalenko, et. al., with an energy resolution of 25% for 59 keV 241Am gamma-rays using formamidinium lead triiodide. PSC detector resolution was improved by Huang, et. al., who demonstrated a 6% energy resolution for 662 keV 137Cs gamma-rays using a methylammonium (MA)-based MAPbBr3-xClx PSC detector.
Despite these initial demonstrations of high-resolution gamma-ray detection using PSC direct detectors, the consistency and scalability of PSC detectors need to be significantly improved, especially to commercialize ultra-low-cost PSC detectors. In terms of consistency, we previously demonstrated a surface-treatment method to significantly improve the energy resolution, yield, and consistency of mm-scale MAPbI3 PSC detectors. To improve scalability, we demonstrated a facile, scalable forced-convection based method to grow PSCs > 2 cm long in less than 2 days of growth time, with very efficient solute utilization in our system. Our axially forced-convection (AFC) method utilizes a crystal growth cell and a precursor solution reservoir. The reservoir holds the 1.0 M MAPbI3 precursor solution below it’s saturation point. The solution is then conveyed to the customized growth cell containing the precursor solution and ITC-grown MAPbI3 seed crystal. The growth cell solution is in the super-saturated condition, enabling epitaxial solution growth of the PSC. We also demonstrate a computer-controlled AFC growth system, capable of a maximum growth rate of > 0.1 cm3 hr-1 when using pulsed-flow. To improve computer control, we also demonstrated computer vision algorithms to determine the PSC volume and solution concentration from crystal growth videos, which fit the PSC edges to determine its volume. These systems can be used not only for facile, scalable, controllable growth of PSCs, but can be broadly extended to both grow and determine the crystallization kinetics of other solution-grown monocrystalline materials.
Keywords: perovskite, crystal growth, radiation detection
Characterization of amorphous selenium films on flexible substrates for development of large area ultraviolet photodetectors (#61)
M. Farahmandzadeh1, S. Abbaszadeh1
1 University of California, Santa Cruz, Electrical and Computer Engineering, Santa Cruz, California, United States of America
Recently, the development of high performance ultraviolet (UV) photodetectors (PDs) has attracted a great amount of attention due to their wide range of applications. Amorphous selenium (a-Se) with a bandgap of 2.2 eV at room temperature is considered as one of the promising UV-sensitive materials. In addition, low melting point, high vapor pressure and ease of deposition allow fabrication of large area UV PDs based on this material. However, long-term stability of a-Se-based PDs against photo-induced effects is an issue that needs to be addressed. The effect of substrate rigidity in radiation-induced defects of stabilized a-Se films was previously investigated; the softer the substrate, the weaker the photo-induced effects. In this work, highly uniform a-Se films were deposited on a 2-inch diameter flexible substrate, polyethylene terephthalate coated with indium tin oxide (ITO-PET). Thickness uniformity and amorphous structure of samples were characterized as an initial step in developing high-performance flexible UV detectors with superb stability. The effect of PET substrate on photo-induced defects within a-Se will be investigated and compared with the results of an a-Se sample deposited on glass.
Keywords: Amorphous selenium, flexible substrate, ultraviolet photodetectors
Passive Gamma-ray Detection with Compact Lightweight Imager for Nuclear Safeguard (#66)
J. Boo1, S. Park1, S. Hyeon1, M. Jeong1
1 Nuclear and Energy Engineering, Jeju National University, Jeju-si, Republic of Korea
Abstract- A compact radiation imaging system capable of detecting, localizing, and characterizing special nuclear materials (SNM, plutonium, and certain types of uranium) would be helpful. The US Department of State prefers passive SNM detection technologies to active interrogation because exposing weapons to fast neutron sources can potentially make them less stable. Meanwhile, neutrons would add new spectral lines which are seen in 58 keV and 202 keV energies owing to the recoil of 127I nuclei in using a traditional scintillator, such as NaI(Tl). To achieve a rapid localization of SNM and sustain spectroscopy capability in a complex gamma/neutron environment, the Jeju National University has currently developed a compact lightweight imager based on coded-aperture, termed EPSILON (Energetic Particle Sensor for the Identification and Localization of Originating Nuclei)-G(gamma). EPSILON-G can read-out 12 × 12 silicon photomultipliers (SiPMs) which is optically coupled with Gd3Al2Ga3O12(Ce) or GAGG(Ce) scintillator array (12 × 12 pixels) with an equivalent pixel pitch of 4.2 mm. The use of GAGG(Ce) scintillator array with excellent detection efficiency and good energy resolution over a wide energy range can facilitate their rapid localization of the stand-off detection of weakly emitting materials, and the result was that 1g of HEU was able to obtain valid images within 2 minutes, 75g of DU was within 10 minutes, and 100g of Uranyl Nitrate Hexahydrate was able to obtain valid images within 4 minutes. In addition, the results of the image acquisition time according to the enrichment of 235U were compared to the possibility of determining the enrichment through spectral comparison analysis. The real-time imaging of gamma-ray emitted from gamma/neutron sources, such as 252Cf, 239PuBe, and 241AmLi is also presented with the corresponding gamma-ray spectra obtained from EPSILON-G.
Keywords: passive SNM detection, compact lightweight imager, gamma-ray imaging in a complex gamma/neutron environment
Light Collection in High-Yield Ultrafast Scintillation Detector based on InAs Quantum Dots Embedded in GaAs Waveguide (#69)
T. Mahajan1, A. Minns1, V. Tokranov1, M. Yakimov1, M. Hedges2, P. Murat3, S. Oktyabrsky1
1 SUNY Polytechnic Institute, Albany, New York, United States of America
Development of high light yield scintillating materials with picosecond time resolution is considered an enabling technology for multiple high-energy physics applications, as well as for medical imaging and security purposes. We have demonstrated that InAs quantum dots (QDs) functioning as luminescence centers within a GaAs matrix stopping material have uniquely fast scintillation properties with high luminescence efficiency and relatively low self-absorption. The advantage arises from efficient radiation energy conversion, fast electron capture in this high-mobility material, and fast radiative recombination in the strongly localized potential of QDs. QD photoluminescence measurement shows about 60% efficiency at room temperature encouraging the normal operating condition for the detector. Considering the parameters of high yield scintillating QD mediums, we have designed a detector consisting of a scintillator crystal which also serves as a waveguide, and a monolithically integrated photodetector to efficiently collect the QD emission. The scintillation response from 241Am alpha-particles were analyzed with both an external photodiode (PD) and an integrated PD which provided an improved optical coupling. Distributions of charge collected by the PD appear bi-modal corresponding to geometry of PD and the WG. The loss of alpha particle energy in air with respect to source-detector separation was observed which enabled the determination of overall detector sensitivity. The mean charge collected by the integrated PD measured by simple readout electronics corresponded to 30 photoelectrons per 1 keV of deposited energy, or ~13% of the theoretically achievable light yield. To measure the transient parameters of the integrated device, the PD was wire-bonded to the input of an 8 GHz IC preamplifier. The scintillation response shows an extremely fast 0.3-0.6 ns decay time and about 70 ps time resolution, limited by the system noise. The response of integrated photodetector was analyzed with the Monte Carlo simulations, which informed design rules for combined optimization of PD and scintillating pixel geometry with respect to the waveguiding properties. The combined light yield and decay time makes the InAs/GaAs QD heterostructures the fastest high yield scintillation material reported.
Keywords: Picosecond Time Resolution, Quantum Dots, Scintillation Detector
High quantum efficiency, radiation hard amorphous silicon based photosensor readout (#75)
A. Saha1, Y. - B. Park2, J. Daniel2, L. J. Guo2, M. Hammig3
1 University of Michigan Ann Arbor, Applied Physics, Ann Arbor, Michigan, United States of America
Traditionally photomultiplier tubes and other gas-filled detectors have been widely used as radiation sensors due to their robust charge transport characteristics and insensitivity to gamma rays. However, the lack of scalability, cost reduction and easy integration into detector scaffolds in gas-filled detectors has steered the market towards silicon-based sensors that are low-power, relatively small, mechanically robust, and easily packaged. While this trend in switching over to silicon is a step in the right direction for detectors, the problem of performance degradation in heavy radiation environments persists. In this study we overcome that by using an amorphous silicon (aSi) based photosensor that replicates the nuclear survivability of gas-filled detectors and has the process-compatibility of the semiconductor industry. Our device structure has been optimized three-fold. First, it suppresses leakage current to below 10 nA, typical of gamma ray detectors. Second, the external quantum efficiency is tuned to 80% and higher by varying the thickness of the aSi layer. Third, the high band gap of aSi makes the device structure radiation hard. Additionally, we have shown a scalability aspect to these devices without compromising the signal detection by adding in capacitance-insensitive amplifier diagnostics. With the use of this amplifier structure, we can detect signals from devices with capacitances as high as 100 pF without signal attenuation and from devices with capacitance upto 100nF with minimal attenuation. These improvements give rise to a device that is low cost, scalable, easy to manufacture and nuclear survivable which makes it desirable in a multitude of radiation detection applications.
Keywords: Amorphous silicon, scintillator readout, radiation hard
A Graphical Approach for Constructing System Matrix for H-RMC used in MLEM-based Image Reconstruction (#81)
J. Lee1, J. - Y. So2, 3, G. Kim4
1 Sejong University, Nuclear Engineering, Seoul, Republic of Korea
The hemispherical Rotational Modulation Collimator (H-RMC) is a radiation imaging system. It can collect radiation from wide directional range (2π). In the previous study, optimal design of H-RMC was introduced and the validity of H-RMC was studied with MCNP6 simulations . In this study, we developed a new H-RMC simulation using MATLAB®, based on the graphical approach in order to generate the modulation curve and the system matrix in greatly reduced of time. This approach creates deterministic results of the modulation pattern for each source position. To show the validity of the MATLAB® simulation results, modulation patterns at various source position were compared to that of MCNP6.
We reconstructed the image of the source by applying Maximum Likelihood Expectation Maximization (MLEM) algorithm  and estimated the position of the source. In this image reconstruction process, system matrix is obtained by MATLAB®, and the modulation pattern is obtained by MCNP6. We calculated signal-to-noise ratio (SNR) and peak signal-to-noise ratio (PSNR) to evaluate the performance.
Keywords: Modulation Pattern, Graphical approach, Image Reconstruction
Scintillation properties of CuInS/ZnS Quantum Dots within plastic scintillator (#83)
C. L. Grove1, I. H. B. Braddock1, M. P. Taggart1, C. Crean1, S. J. Sweeney1, P. J. Sellin1, C. Shenton-Taylor1
1 University of Surrey, Department of Physics, Guildford, United Kingdom
The exciton confinement of quantum dots (QD) can lead to optical and electrical properties not exhibited within bulk material of the same composition. The addition of QDs can increase and potentially tune the response of a scintillator to radiation. This work reports the luminescence of CuInS/ZnS QDs, suspended both within toluene and a loaded layer in solid polyvinyl toluene-based plastic scintillators (EJ-290). Under 405 nm laser excitation, liquid toluene dispersed CuInS/ZnS QDs peak photoluminescence occurred at 547.7±0.8 nm. Optical absorption spectra of QD loaded toluene allowed calculation of the Stokes shift, measured at 180±1 nm. CuInS/ZnS QD loaded layers ranging from 40 mg to 200 mg were established within 1 cm3 cubes of EJ-290, confirmed through energy-dispersive X-ray spectroscopy. The 120 mg QD loaded layer recorded atomic percentages of 4.2±0.4 % zinc and 2.0±0.4 % sulphur. Photoluminescence emission spectra from both loaded and unloaded cast scintillators were compared; each sample with a QD layer showed increased emission brightness over unloaded EJ-290. Relative to unloaded EJ-290 emission, the 120 mg QD loaded sample photoluminescence peak integral was 1.14 larger, rising to 16.75 for a 200 mg CuInS/ZnS layer. The plastic scintillators were placed 5 cm from an X-ray source, where the dose rate was 0.1145±0.0009 Gy s-1. In all cases, X-ray luminescence from the QD loaded samples showed increased intensity over unloaded scintillator material. Specifically, the 120 mg CuInS/ZnS loaded sample had an X-ray luminescence peak integral of 4.20 larger than unloaded EJ-290. The inclusion of CuInS/ZnS QDs within EJ-290 brings both increased brightness but also material cost. However, QD dopants may offer scintillator performance benefits for radiation detection within homeland security applications, such as increased γ and X-ray detection efficiency through higher average atomic number and wavelength shifting to match photodetector spectral resolution more closely.
Keywords: Quantum dots, Plastic scintillators, Nanocomposites
Markov Chain Monte Carlo Uncertainty Quantification for Shielded Point Source Localization (#99)
J. R. Vavrek1, M. S. Bandstra1, D. Hellfeld1, B. J. Quiter1, K. Meehan1, P. J. Barton1, J. W. Cates1, A. Moran1, V. Negut1, R. Pavlovsky1, T. H. Joshi1
1 Lawrence Berkeley National Laboratory, Applied Nuclear Physics group, Berkeley, California, United States of America
We demonstrate Markov Chain Monte Carlo (MCMC) methods for radiological source quantification and localization in the presence of shielding. Branching off of a complementary maximum likelihood technique (ML) by Bandstra et al. (2021), we use the PyMC3 package to build an MCMC model of the counts reaching a detector as it moves about the scene. Using the attenuation map computed in the course of the ML analysis and developing priors for the MCMC model based on the ML result, we show that the MCMC results for source activity, location, and attenuation length agree well with the ML analysis. Moreover, the MCMC model automatically generates parameter uncertainty estimates, and is more extensible to possible future analyses such as the effect of detector efficiency uncertainties.
Keywords: gamma-ray imaging, uncertainty quantification, shielding
High efficiency semiconductor for hard X-ray imaging (#110)
H. Kim1, L. Cirignano1, Y. Ogorodnik1, S. Kim1, J. Christian1, K. Shah1, B. Allen2, J. Clayton3
1 RMD Inc, Watertown, Massachusetts, United States of America
Thallium bromide has been under development as a denser, higher Z, potentially lower cost alternative to CZT as a room-temperature X and gamma-ray detector material. This paper will report on the fabrication and performance of pixelated TlBr arrays 4 to 5 mm thick with 0.6 mm pitch. Preliminary testing (spectroscopy) with NIM electronics, flatness measurements of the arrays as well as testing (spectroscopy and imaging) with the arrays bonded to the NuSTAR ASIC will be presented.
Keywords: thallium bromide, hard X-Ray imaging, NuSTAR ASIC
Improved Radiation Sensing with Methylammonium Lead Bromide Perovskite Semiconductors (#111)
J. Charest1, 2, R. Tan1, 2, B. Dryzhakov3, 2, K. Higgins3, 2, A. Naylor1, 3, C. Busch1, 3, B. Hu3, 2, M. Ahmadi3, 2, E. Lukosi1, 3
1 University of Tennessee, Knoxville, Nuclear Engineering, Knoxville, Tennessee, United States of America
This presentation will report several techniques under investigation to improve the spectroscopic capability of methylammonium lead tribromide perovskite semiconductors (CH3NH3PbBr3, or MAPB). These techniques include the use of chemo-mechanical processing techniques to perfect surface quality, limit surface recombination, and improve charge collection efficiency. Furthermore, we will present the first reported electron carrier properties for MAPB in response to ionizing radiation with the implementation of stabilizing metal oxide layers at the contact interface. Finally, further efforts to implement single carrier charge sensing techniques for gamma spectroscopy will be discussed.
Keywords: MAPB, Surface treatments, Tin oxide
Gaseous detector with boron-coated blades in multi-grid configuration for fast neutron detection in homeland security and waste monitoring applications (#115)
P. Karpowicz1, A. Dziedzic1, K. Grodzicki1, B. Guerard2, S. Mianowski1, S. Partyka3, L. Swiderski1, A. Syntfeld-Każuch1
1 National Centre for Nuclear Research (NCBJ), Otwock, Poland
In this presentation we report on the construction and performance of a gaseous detector with boron-coated blades in multi-grid configuration for fast neutron detection. The aim of this project is to adapt a solution originally designed for neutron scattering experiments and use it for detection of fast neutrons by adding appropriate polyethylene (PE) shielding. Multi-grid configuration of thin layers covered with boron-10 enriched material was proposed as an alternative to He-3 neutron counters due to rise He-3 price and limited accessibility. In the course of this study we characterize the performance of a small size evaluation kit detector equipped with sets of aluminum blades covered with boron-10 nanoparticles manufactured by Lubrina company (Lodz, Poland). The detector contains aluminium grids that form 4 readout channels. Inner walls of each channel are covered with a thin layer of neutron converter. In the centre of each channel there is an anode wire placed fixed to two PE rollers at the top and bottom of the detector assembly. The outer detector vessel is an aluminum cylinder filled with Ar/CO2 gas mixture. The detector was operated under continuous flow of gas mixture pressurized slightly above atmospheric pressure. The test measurements were carried out using Cf-252 and PuBe neutron sources and an intense Cs-137 gamma-ray source. In order to moderate neutrons and increase detection efficiency, the test detector was surrounded with PE bricks forming a castle. This report presents the results obtained for 5 sets of grids with boron thickness between 1.0 µm and 3.0 µm with a step of 0.5 µm. In addition, a He-3 neutron counter was used in the same experimental conditions for comparison. The results of the laboratory tests were used to evaluate the size and to design a full scale detection system that will fulfil requirements for neutron detection system in homeland security and waste monitoring applications.
Keywords: boron neutron converter, homeland security, border monitoring
Linear charge or voltage-amplitude to pulse-width conversion for position sensitive detector readout (#130)
L. Liu1, 2, Y. Yang1, 2, Y. Yu1, 2, Z. Zhang1, 2
1 Tsinghua Univeristy, 1Department of Engineering Physics, Beijing, China
A transistor based linear discharge method to achieve linear voltage-amplitude to pulse-width conversion was proposed. In this circuit, the charge sensitive preamplifier was discharged through a constant current, thus the time over the threshold is linear to the input charge or voltage amplitude of the preamplifier. A universal field programmable gate array uses just one IO to realize a channel in position sensitive detectors, which greatly simplify the high-speed analog-to-digital converters used in the traditional center of gravity method. The circuit overcomes the exponential decay signal of the classical resistive feedback preamplifier and provides a way to enable a high throughput rate and low noise. The feedback capacitor and discharge time can be easily changed and provides great flexibility to adapt diverse signals of various detectors. This circuit shows to be a simple and elegant readout for position sensitive detectors.
Keywords: voltage-amplitude to pulse-width conversion, linear, position sensitive detector readout
Dual-Particle Imaging Performance of Cs2LiYCl6:Ce (CLYC)-based Rotational Modulation Collimator (RMC) Radiation Imager (#131)
H. S. Kim1, S. - J. Ye2, G. Kim3
1 Korea Institute of Nuclear Safety, Daejeon, Republic of Korea
For the development of a dual-particle imager capable of visualizing both neutrons and gammas, the rotational modulation collimator (RMC)-based imaging technique was attempted as an economical and effective approach which offers less complexity in the system configuration [1,2]. Recently, we have suggested an RMC imaging system combined with the pulse shape discrimination (PSD)-capable Cs2LiYCl6:Ce (CLYC) scintillation detector as a dual-particle imager. Batches of Monte Carlo simulations were performed to investigate the feasibility of developing CLYC-based RMC system, and an image reconstruction algorithm implementing maximum-likelihood expectation-maximization (MLEM) approach was developed. We also optimized the collimator mask design parameters for the dual-particle imaging purpose and proposed a new asymmetric mask design to remove the ambiguous artifact without compromising the imaging capability . In this work, we report the dual-particle imaging performance of the newly-developed dual-particle imager with imaging capability at a mid-range field using gamma-ray and neutron sources. Recent results on the CLYC-based RMC measuring multiple sources and imaging them will be reported, and the imager’s performance in a mixed neutron/gamma-ray environment will be evaluated. The signal-to-noise ratio and the structural similarity index was calculated to evaluate reconstructed images of the source distributions quantitatively. Measurement results showed that the modulation patterns obtained from the RMC imager showed good repeatability and reproducibility and well-matched simulation results. Reconstructed images were shown to make good estimations on the radiation source location. Both gamma rays and neutrons can be visualized to estimate the source location of radioactive materials utilizing a CLYC-based RMC system.
Keywords: Dual-particle imager, Rotational Modulation Collimator (RMC), Radiation Imaging
A Hand-Portable, Field-Deployable Imaging Neutron Detector (iFIND) for SNM (#142)
J. Legere1, P. Bloser3, C. Ertley2, M. McConnell1, 2, J. Ryan1
1 University of New Hampshire, Space Science Center, Durham, New Hampshire, United States of America
Neutron detection is of particular interest for nuclear or radiological material identification for security and proliferation deterrence, as well as for nuclear waste detection and monitoring. This paper describes the Hand-Portable Field-Deployable Imaging Neutron Detector (iFIND), currently under development. The iFIND instrument concept follows the successful Field-deployable Imaging Neutron Detector (FIND) program at the University of New Hampshire. The FIND instrument was based on modern, commercially available detector technology that is compact, low-power, low-mass, and rugged, but discrete electronic channels were used for detector readout. These electronics can be bulky and have modest power requirements. Newly available application-specific integrated circuits (ASICs) designed for pulse-height and time-of-flight (ToF) measurements using silicon photomultipliers (SiPMs) permit flexible designs with more channels and reduced power. The use of an ASIC allows an increased number of smaller detector elements to be read out in a more compact, efficient configuration while simultaneously reducing the instrument size, weight, and power. Smaller scintillator elements will result in a lower trigger threshold and improved ToF and energy resolution, making a more efficient detector. A portable, modular, and scalable system architecture, iFIND, can thus finally be realized. We describe the development of the iFIND instrument in detail and present initial imaging and spectroscopy results from laboratory in conjunction with simulations.
Keywords: Neutron Imaging, Neutron Spectroscopy, SNM Detection
The feasibility of neutron interrogation as dry cask storage inspection (#151)
K. T. Lim1, S. Kim1, M. Kim1, Y. Kim2, H. Chung1
1 Korea Institute of Nuclear Nonproliferation and Control, Daejeon, Republic of Korea
South Korea currently lacks dry storage for LWR power plants. However, the establishment of dry storage is inevitable as many LWR fuel pools are expected to reach their capacities, starting with the Hanbit nuclear power plants in 2029. The increasing need for a dry storage solution will continue to grow in South Korea as no permanent repository sites are currently available. In fact, it became apparent that the capacity of wet storage is reaching its limit in other countries, a result that necessitates a dry-storage solution. Hence, the demand for establishing safeguards and verification techniques for maintaining the integrity of spent nuclear fuels (SNF) inside dry casks has increased globally.
In this work, we demonstrate the feasibility of using neutron interrogation in safeguards and verification of SNF in dry casks. In particular, we adopted a tomographic approach to explore the unique signatures of emitted neutrons for dry cask inspection through a lab-scale demonstration. The Arktis S670e He-4 scintillation detectors were chosen for measuring fast and thermal neutrons, owning to their ability to detect both fast and thermal neutrons while offering a high gamma-rejection probability. Borated polyethylene collimators were installed between adjacent He-4 detectors to adjust the field of view on neutron distribution. A 1/10th model cask was also built to mock-up the dry storage, and a 252Cf source was placed inside the model cask as a test bench. While having 252Cf source inside the cask, the He-4 detector array was positioned close to the cask model and emitted neutrons were measured simultaneously from 0° to 360° at 10° interval. Then, a MATLAB script was used to implement the acquired projection data and perform tomographic image reconstruction through the filtered back-projection. Furthermore, MCNP simulation was performed to intercompare the experimental results with computational ones.
Keywords: neutron interrogation, neutron tomography, He-4 detector
Passive Gamma-Ray Imaging of Special Nuclear Materials using a Handheld Dual Particle Imager (#152)
W. M. Steinberger1, N. Giha1, R. Lopez1, J. Nicholson2, S. Clarke1, S. Pozzi1
1 University of Michigan, Nuclear Engineering and Radiological Sciences, Ann Arbor, Michigan, United States of America
A handheld dual-particle imager (H2DPI) composed of twelve stilbene pillars (6 x 6 x 50.5 mm3) and eight CeBr3 cylinders (6 x 6 Φ mm3) coupled to J-series SensL silicon photomultipliers has been designed and built. Gamma-ray imaging is performed by reconstructing double-scatter events between organic and inorganic scintillators to localize gamma-ray emitting sources. The key benefit to performing Compton imaging by reconstructing gamma-ray interactions between the two types of scintillators is being able to assume the sequencing of the interactions with a high degree of certainty. It is assumed that gamma rays that deposit their full energy when interacting with both a stilbene pillar and CeBr3 cylinder must have undergone Compton scattering in the stilbene pillar and photoelectric absorption in the CeBr3 cylinder. This Compton imaging methodology was shown to accurately reconstruct gamma-ray sources such as 137Cs and 22Na. To further test this methodology, a mock 10-kg equivalent highly enriched uranium (HEU) sphere and a 100-g disk of plutonium were measured at Savannah River National Laboratory. The sphere is an object designed to have a gamma-ray signature consistent with a 10-kg sphere of HEU. The sources were measured independently and in the same field of view. In both cases, the H2DPI was able to accurately reconstruct the two sources by passively imaging the emitted gamma rays.
Keywords: Compton Imaging, Special Nuclear Material, SiPMs
The Effect of Wavelength Shifting Fibers on Cherenkov Glass Detectors to Detect Gamma Rays (#153)
H. Natto1, H. Yang1
1 Oregon State University, Nuclear Science and Engineering Department, Corvallis, Oregon, United States of America
Cherenkov detectors have been developed and used in several fields since the discovery of Cherenkov radiation. They have several advantages compared with other detector types, such as producing light output for easy detection using common photon sensors, low noise due to the low-energy threshold of Cherenkov radiation, and Cherenkov photons are emitted in a very short time (in the order of picoseconds) which make Cherenkov detectors remarkably fast. However, the yield of Cherenkov photons is low. Only several hundred of Cherenkov photons could be generated per MeV. The objective of this work is to produce and test Cherenkov glass detectors for detection of high gamma rays from an isotropic 60Co source. The focus is to improve the yield of Cherenkov photons by implementing Wavelength Shifting (WLS) fibers inside the glass samples. Without the WLS materials, the majority of Cherenkov photons are likely to be absorbed within the glass sample before they would reach the photocathode. These fibers cannot directly increase the number of optical photons. However, they can only reduce the energy of Cherenkov photons so that they can propagate further in the glass sample and are more likely to create photoelectrons on the photocathode.
design of photoneutron sources based on different power and energy e-linac (#155)
L. Lu1, X. Wang1, Y. Yang1
1 Tsinghua University, Haidian District, Beijing, China
It is an urgent demand in the industrial application to detect the residual core material of the gas-cooled turbine blade, drug, explosive, and so on by neutron imaging. It need a neutron source with enough thermal neutron flux (>103n/cm2/s), producing continuous energy spectrum in thermal neutron energy region. The photoneutron source meets the above requirements. Besides, it’s the advantage of long life-span high yield and compact structure. Two photoneutron sources based on the 7-MeV/100-W and 9-MeV/900-W e-linacs have been built in the Tsinghua University to realize the above application. To improve the thermal neutron flux, the power and energy of the e-linac will be improved. When the energy of the e-linac is increased, the neutron yield will be increased because of the larger cross section of the (γ,n) reaction. At the same time, the electron per second will be less with the larger energy of the e-linac under circumstance of the same e-linac power, which will cause the lower neutron yield. To find the suitable parameter, the relationship between thermal neutron flux and power and energy of the e-linac is researched.
Keywords: photoneutron source, thermal neutron imaging, the e-linac energy and power
Optimization of Hot Pressing Conditions for Improved Light Transmission in Li5La3Ta2O12 Ceramics for Dual-Mode Detectors (#156)
J. Smith1, 2, K. Sickafus3, C. - F. Chen4, C. Melcher1, 2, 3
1 The University of Tennessee Knoxville, Scintillation Materials Research Center, Knoxville, Tennessee, United States of America
Recent studies of a family of Li-containing garnet compounds for their use in Li-ion solid electrolyte applications, because of their cubic structure and high Li content, have created an interested in their potential to be developed into transparent ceramic dual-mode scintillators. In particular, Li5La3Ta2O12 (LLTO) shows promise as an efficient dual-mode scintillator due to its high Li content, high density, non-hygroscopicity, high effective-Z and intrinsic tantalate emission. A flexible alkoxide sol-gel method has been developed for the synthesis of LLTO powders that are then consolidated via uni-axial hot pressing. This work focuses on the optimization of the hot-pressing conditions to balance grain growth and pore removal rates to result in highly translucent, closed porosity ceramics for future removal of residual porosity by hot isostatic pressing. Pure and Pr, Eu or Ce doped LLTO powders were made with 15% excess Li to compensate for the volatility of Li during calcining, crystallizing, consolidation and thermal annealing. Powders were first pressed into green bodies in a 13mm diameter stainless steel die at 167 MPa and then loaded into a grafoil-lined graphite die for hot pressing under vacuum at a range of temperatures, pressures and times. Hot pressed ceramics were than characterized by: the Archimedes method to determine density, x-ray diffraction to determine phase purity, UV-Vis transmission to determine the degree of translucency through in-line transmission, and scanning electron microscopy and electron backscatter diffraction to analyze the microstructure of the ceramics.
Keywords: Ceramic, Dual-mode, Lithium
MaterialsSegmentation of API Imaging Using Neutron-Induced Gamma Spectra (#158)
B. Canion1, R. Wurtz1, L. Fabris2, I. Garishvili2, A. Glenn1, P. Hausladen2, M. Heath2, D. Lee1, S. McConchie2, L. Nakae1, J. Newby2
1 Lawrence Livermore National Laboratory, Livermore, California, United States of America
An associated particle imager (API) provides a spatial and temporal tag on events detected from a neutron-interrogated target, as well as providing a convenient veto to help suppress all events not associated with interrogating neutrons. A gamma spectrometer correlated in time with the paths of interrogating neutrons provides the ability to reconstruct a three-dimensional spectral image, composed of gamma-rays induced from neutron interactions in the target material. We are designing an API-based system to use this signature to discern the distributions and types of material in a target based in part on neutron-induced gamma spectra associated with the 3D voxels. We will demonstrate how to observe differences of material and obtain material boundaries using unsupervised methods of comparing gamma spectra among voxels. We will also demonstrate how to obtain material composition both by extracting dominant spectral differences in different regions, and by comparison to adequate nuclear data. We will show how a few issues affect the outcome, including signal to noise, timing and spatial precision of the API, spectral resolution of the gamma detector, correctness and completeness of nuclear data libraries, and distinctiveness of the inelastic spectra of different materials.
Keywords: associated particle imaging, neutron interrogation, inelastic gamma spectroscopy
Hafnium Oxide Nanoparticles Loaded Liquid Scintillators for Gamma Ray Spectroscopy (#159)
H. Yu1, H. Zhao1, T. J. Hajagos1, C. Redding2, G. Ferrelli3, T. Chen1, Z. Han1, J. Hayward2, R. Zaldivar3, Q. Pei1
1 University of California, Los Angeles, Department of Materials Science and Engineering, Los Angeles, California, United States of America
Spectroscopic detection of gamma photons has widespread applications for high-energy physics research, threat detection and medical diagnosis. The dominant materials for the scintillation detectors have been inorganic crystals, organic liquids and plastics. However, current commercial detectors tend to be either expensive for large-size, large-scale deployment or incapable of producing the charateristic gamma photopeaks, which can lead to reduced performance compared with those that do yield photopeaks. Herein, we report the syntheses of transparent liquids comprising high loading of hafnium oxide (HfO2) nanoparticles for gamma photoelectric effect generation. The high effective atomic number (Zeff=68.8) and density (9.7 g/cm3) of the HfO2 nanoparticles renders the liquid scinitllators to have a more significant photoelectric cross-section. The energy transfer from the aromatic solvent to the luminescent dyes via the conjugated organic compound are additionally investigated to boost the visible photon production. Various factors affecting the synthesis, the optical transparency, the light yield and the radiation hardness were studied. A conjugated co-solvent with bandgap smaller than that of toluene was found to increase the light yield. Conventional organic dyes, such as 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole (PBD) as a primary dye and 1,4-bis(5-phenyloxazol-2-yl) benzene (POPOP) as a secondary dye were also added in the solution. The scintillators retain a high transparency in the emission wavelength range, achieving a transmittance up to 80% at nanoparticle loadings as high as 50 wt% for a sample thickness of 2 mm. The measured scintillation light collection declines with increasing concentration of the nanoparticles, but remain at fairly high values at up to 40 wt% loading. A full energy 137Cs photopeak has been detected on a 2 mm-thick liquid scintillator sample loaded with 20 wt% HfO2 nanoparticles. A relatively large volume of liquid scintillator (6.3 mL) loaded with 40 wt% HfO2 nanoparticles of 20 mm thickness has also been prepared which produced a gamma photopeak with 15% energy resolution. The 2 mm-thick liquid scintillator loaded with 20 wt% HfO2 nanoparticles retained 95% transmittance and 70% light collection compared with its original value after exposure to 9 MRad of gamma irradiation. In general, radiation hardness measurements show that the presence of high-Z nanoparticles has only a modest effect on the transmittance and scintillation light collection.
Keywords: scintillator, nanoparticles, energy resolution
Benchmarking of NNLS application to a proof-of-concept gamma source imaging system (#165)
N. Anuar1, C. Marianno1
1 Texas A&M University, Department of Nuclear Engineering, College Station, Texas, United States of America
A proposed system for imaging gamma source utilizing non-negative least square (NNLS) method was designed using Monte Carlo N-Particle (MCNP) simulations and validated with experimental measurements. The validation was performed for four cases with different pre-defined source locations. The experimental set up was also tested with an "unknown" source location without any simulation results to compare with. A validation metric, defined as the estimated error, E was determined for each case's measurement. The E value was plotted together with 90% experimental confidence interval, and with 90% true error confidence interval to evaluate the proposed system's performance. Two global metrics, the average and maximum relative errors with the respective 90% confidence interval, were also presented in the analysis. In addition to quantitative evaluation of the simulation and experimental results, qualitative evaluation was also made for each case. It was found that the localization was successful in all four cases, including the "unknown" source location, despite the presented modeling errors. This demonstrated that the imaging concept of the proposed system is robust and is worth further investigation. This could contribute to the development or integration of potential new technology for counter-terrorism activities.
Keywords: Gamma source imaging, non-negative least square
Integration-type CdTe pseudo-energy discriminating X-ray line sensor for high-energy imaging (#169)
T. Aoki1, 2, 3, K. Kimura2, K. Toyoda3, H. Kase2, 1, 3, A. Koike3, 1, T. Terao3, K. Tabata1, K. Takagi1, 3
1 Shizuoka University, Research Institute of Electronics, Hamamatsu, Japan
We have developed and reported a charge integration CdTe imaging device, a flat panel imager. This imager consists of a tiling of 100 µm pixel modules with an imaging area of approximately 2.3 cm x 1.2 cm. Normally, this imaging device performs two-dimensional imaging sensor by injecting X-rays from above the plane. In this study, we injected X-rays from the lateral direction of the plane to make it work as an X-ray line sensor with a sensitive layer of about 2.3 cm, which is a sensor with high energy and high sensitivity. In the depth direction, the pixels have a pitch of 100 µm, and the X-ray photon energy can be roughly estimated using the X-ray photon penetration length. We developed the device design, readout circuit, and signal processing for this purpose. Although this method cannot completely separate the energy and quantity of X-ray photons, and is only a pseudo-energy discrimination, but it can be used to roughly identify materials and remove image interference caused by scattered radiation.
CdTe, which has a high linear attenuation coefficient, can be used with a large attenuation length and a large dynamic range with charge integration mode for CW and pulse X-ray souse each as X-ray tube and accelerator, so it is expected to be used in high energy sources such as accelerator sources.
Keywords: High energy, CdTe, pseudo-energy discrimination
Design and Fabrication of Efficient PSD in Polysiloxane-based Scintillators (#175)
C. Chandler1, J. Arrue2, A. Sellinger1, A. Erickson2
1 Colorado School of Mines, Chemistry, Golden, Colorado, United States of America
On behalf of ETI Consortium, Thrust Area 3, Project 1
One component of national security is monitoring borders for potentially dangerous nuclear material. This is currently accomplished using large area radiation portal monitors that vehicles pass through as they enter and exit the country. These devices contain an active plastic scintillator component that produces optical light when interacting with ionizing radiation. That optical light is then measured using a photodetector and analyzed for a characteristic signal. With this technology, materials like plutonium or uranium can be identified however benign radiation emitters like bananas, kitty litter, or granite slabs can cause undesired false positives. While there are several benign emitters that produce gamma rays, neutrons are produced solely by nuclear material of interest for national security. The research discussed here focuses on the development of materials for large area scintillators capable of differentiating between the radiation signatures of neutrons (plutonium) and gammas (bananas).
This characterization of different radiation signatures can be accomplished through pulse shape discrimination, which analyzes the decay time of light produced by a scintillator to identify the type of incident ionizing radiation. Pulse shape discrimination is only possible in a select few types of plastic scintillators. Plastic scintillators are generally composed of a matrix material that is doped with a primary and secondary dopant. Poly(vinyltoluene) is the most common matrix material used in radiation portal monitors, but has only been able to achieve efficient pulse shape discrimination at large doping levels (> 20 wt%), that is undesirable. Using large amounts of dopant causes issues related to the mechanical properties of the scintillator and the precipitation of dopant molecules. In this talk, the synthesis, analysis, and development of doped polysiloxanes will be discussed, with the goal to discriminate gammas and neutrons efficiently. Polysiloxanes offer several advantages over the plastic scintillator materials used currently in radiation portal monitors, most importantly the ability to achieve efficient pulse shape discrimination at low dopant levels. This behavior has only been achieved in one commercially produced composition of polysiloxane. This research aims to understand, emulate, and improve upon that successful composition to help develop another class of PSD-capable plastic scintillator.
Keywords: Scintillators, Polysiloxanes, Pulse Shape Discrimination
A Detector Array for the Measurement of the Energy and Direction of Neutrons from Remote Sources* (#177)
C. Shahi1, R. Haun1, L. Lutz1, J. Graybill2, L. Putnam1, M. Coplan1, 2, C. Clark1, A. Parsons1, T. Livengood3, J. J. Su4
1 University of Maryland, College Park, United States of America
Aneutron detector consisting of an array of basic unit cells has been developed. Each cell uses the products of the 10B(n, ????)7Li reaction to produce scintillation in xenon gas which is recorded by silicon photomultipliers. Each basic cell is fitted with a different combination of high-density polyethylene and cadmium attachments that modify the response of the individual cells. When combined with machine learning algorithms, the responses of the cells are used to derive both the direction and energy distribution of neutrons from remote sources. The array is mechanically robust, operates with low power and low voltage, has low gamma ray sensitivity, can be configured in a range of geometries and is scalable according to specific applications. The example of the measurement of spallation neutrons on the surface of the Moon will be discussed.