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Nuclear Science, IEEE Transactions on

Issue 2  Part 1 • Date April 2013

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Displaying Results 1 - 25 of 137
  • [Front cover]

    Publication Year: 2013 , Page(s): C1
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  • IEEE Transactions on Nuclear Science publication information

    Publication Year: 2013 , Page(s): C2
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  • Table of contents

    Publication Year: 2013 , Page(s): 473 - 479
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  • Editorial Conference Comments by the Editors

    Publication Year: 2013 , Page(s): 480 - 481
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  • Performance of a Fisher Linear Discriminant Analysis Gamma-Ray Identification Algorithm

    Publication Year: 2013 , Page(s): 482 - 489
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1185 KB) |  | HTML iconHTML  

    The development of a gamma-ray identification algorithm based on a Fisher Linear Discriminant Analysis (FLDA) approach has previously shown high potential in count starved situations. This work uses 48,000 semi-empirical synthetic spectra to evaluate the algorithm performance over a broad range of dose rates and acquisition times. True positive identifications of 100% were typically seen for dose rates ≥ 0.05 μSv/h and acquisition times ≥10 s. For in air and shielded radionuclide spectra, no false alarms were observed for dose rates ≥ 0.01 μSv/h and acquisition times ≥10 s. The single radionuclide identification performance typically exceeded the ANSI 42.34 standard by a factor of 10 for dose rate and a factor of 10 for acquisition time. The evaluated shielded signatures had no detrimental effects to the identification performance. The correct identification of HEU masked by a 0.5 μSv/h 40K or 60Co source could typically be made for a masking ratio of 10:1 for acquisition times ≥ 1 s. For masking with a 0.5 μSv/h 137Cs source, HEU could be identified at 7:1 ratios for times ≥10 s. The excellent results were obtained for a non-optimal identification threshold. Optimization of the threshold would lead to further performance improvements. View full abstract»

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  • Monte Carlo Simulations for Small Electron Field Size Irradiation

    Publication Year: 2013 , Page(s): 490 - 494
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (723 KB) |  | HTML iconHTML  

    Fricke Xylenol Gel (FXG) is a chemical dosimeter based on swine skin gelatin, Xylenol Orange (XO) and ferrous sulphate. When irradiated with ionizing radiation, absorbed dose distributions and profiles can be inferred through spectrophotometric techniques due to the [Fe+3-XO] complex absorbencies, which are field size and post irradiation time dependent. Although these two dependencies have already been experimentally considered in literature, theoretical models have not been extensively explored. In this work, a Monte Carlo Method (MCM) simulation was proposed in order to assess electron beam profiles for: variable field size and post irradiation time. The proposed simulational model describes the above processes, in a similar way when FXG samples are irradiated with megavoltage electrons, i.e., transition from Gaussian-like profiles to step functions (small to large fields, respectively) and Gaussian time dependent curves for diffusion effects (Fokker-Planck theory), indicating that this transition is primarily controlled by the beam geometric factors and the radiation random nature. View full abstract»

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  • Monte Carlo Simulation of X-Ray Spectra in Mammography and Contrast-Enhanced Digital Mammography Using the Code PENELOPE

    Publication Year: 2013 , Page(s): 495 - 502
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (571 KB) |  | HTML iconHTML  

    In this work, the Monte Carlo (MC) code PENELOPE was employed for simulation of x-ray spectra in mammography and contrast-enhanced digital mammography (CEDM). Spectra for Mo, Rh and W anodes were obtained for tube potentials between 24-36 kV, for mammography, and between 45-49 kV, for CEDM. The spectra obtained from the simulations were analytically filtered to correspond to the anode/filter combinations usually employed in each technique (Mo/Mo, Rh/Rh and W/Rh for mammography and Mo/Cu, Rh/Cu and W/Cu for CEDM). For the Mo/Mo combination, the simulated spectra were compared with those obtained experimentally, and for spectra for the W anode, with experimental data from the literature, through comparison of distribution shape, average energies, half-value layers (HVL) and transmission curves. For all combinations evaluated, the simulated spectra were also compared with those provided by different models from the literature. Results showed that the code PENELOPE provides mammographic x-ray spectra in good agreement with those experimentally measured and those from the literature. The differences in the values of HVL ranged between 2-7%, for anode/filter combinations and tube potentials employed in mammography, and they were less than 5% for those employed in CEDM. The transmission curves for the spectra obtained also showed good agreement compared to those computed from reference spectra, with average relative differences less than 12% for mammography and CEDM. These results show that the code PENELOPE can be a useful tool to generate x-ray spectra for studies in mammography and CEDM, and also for evaluation of new x-ray tube designs and new anode materials. View full abstract»

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  • Parameterized Radiation Transport Model for Neutron Detection in Complex Scenes

    Publication Year: 2013 , Page(s): 503 - 509
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1080 KB) |  | HTML iconHTML  

    There is interest in developing the ability to rapidly compute the energy dependent neutron flux within a complex geometry for a variety of applications. Coupled with sensor response function information, this capability would allow direct estimation of sensor behavior in multitude of operational scenarios. In situations where detailed simulation is not warranted or affordable, it is desirable to possess reliable estimates of the neutron field in practical scenarios which do not require intense computation. A tool set of this kind would provide quantitative means to address the development of operational concepts, inform asset allocation decisions, and exercise planning. Monte Carlo and/or deterministic methods provide a high degree of precision and fidelity consistent with the accuracy with which the scene is rendered. However, these methods are often too computationally expensive to support the real-time evolution of a virtual operational scenario. High fidelity neutron transport simulations are also time consuming from the standpoint of user setup and post-simulation analysis. We pre-compute adjoint solutions using MCNP to generate a coarse spatial and energy grid of the neutron flux over various surfaces as an alternative to full Monte Carlo modeling. We attempt to capture the characteristics of the neutron transport solution. We report on the results of brief verification and validation measurements which test the predictive capability of this approach over soil and asphalt concrete surfaces. We highlight the sensitivity of the simulated and experimental results to the material composition of the environment. View full abstract»

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  • Alternatives for Helium-3 in Multiplicity Counters

    Publication Year: 2013 , Page(s): 510 - 514
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1199 KB) |  | HTML iconHTML  

    Alternatives to helium-3 are being actively pursued due to the shortage and rising costs of helium-3. For safeguards applications, there are a number of ongoing investigations to find alternatives that provide the same capability in a cost-effective manner. One of the greatest challenges is to find a comparable alternative for multiplicity counters, since they require high efficiency and short collection or die-away times. Work has been progressing on investigating three commercially available alternatives for high efficiency multiplicity counters: boron trifluoride (BF3) filled proportional tubes, boron-lined proportional tubes, and lithium fluoride with zinc sulfide coated light guides. The baseline multiplicity counter used for the investigation is the Epithermal Neutron Multiplicity Counter with 121 helium-3 filled tubes at 10 atmosphere pressure, which is a significant capability to match. The primary tool for the investigation has been modeling and simulation using the Monte Carlo N-Particle eXtended (MCNPX) radiation transport program, with experiments to validate the models. To directly calculate the coincidence rates in boron-lined (and possibly other) detectors, the MCNPX code has been enhanced to allow the existing coincidence tally to be used with energy deposition rather than neutron capture reactions. This allows boron-lined detectors to be modeled more accurately. Variations of tube number and diameter along with variations in the amount of inter-tube moderator have been conducted for the BF3 and boron-lined cases. Tube pressure was investigated for BF3 , up to two atmospheres, as well as optimal boron thickness in the boron-lined tubes. The lithium fluoride was modeled as sheets of material with light guides in between, and the number and thickness of the sheets investigated. The amount of light guide, which in this case doubles as a moderator, was also optimized. The results of these modeling and simulation optimiza- ion investigations are described and results presented. View full abstract»

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  • Analysis of Photon Scattering Trends for Material Classification Using Artificial Neural Network Models

    Publication Year: 2013 , Page(s): 515 - 519
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (845 KB) |  | HTML iconHTML  

    In this project, we concentrate on using the Artificial Neural Network (ANN) approach to analyze the photon scattering trend given by specific materials. The aim of this project is to fully utilize the scatter components of an interrogating gamma-ray radiation beam in order to determine the types of material embedded in sand and later to determine the depth of the material. This is useful in a situation in which the operator has no knowledge of potentially hidden materials. In this paper, the materials that we used were stainless steel, wood and stone. These moderately high density materials are chosen because they have strong scattering components, and provide a good starting point to design our ANN model. Data were acquired using the Monte Carlo N-Particle Code, MCNP5. The source was a collimated pencil-beam projection of 1 MeV energy gamma rays and the beam was projected towards a slab of unknown material that was buried in sand. The scattered photons were collected using a planar surface detector located directly above the sample. In order to execute the ANN model, several feature points were extracted from the frequency domain of the collected signals. For material classification work, the best result was obtained for stone with 86.6% accurate classification while the most accurate buried distance is given by stone and wood, with a mean absolute error of 0.05. View full abstract»

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  • MCNP Simulation Benchmarks for a Portable Inspection System for Narcotics, Explosives, and Nuclear Material Detection

    Publication Year: 2013 , Page(s): 520 - 527
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (949 KB) |  | HTML iconHTML  

    MCNPX simulations have been used to guide the development of a portable inspection system for narcotics, explosives, and special nuclear material (SNM) detection. The system seeks to address these threats to national security by utilizing a high-yield, compact neutron source to actively interrogate the threats and produce characteristic signatures that can then be detected by radiation detectors. The portability of the system enables rapid deployment and proximity to threats concealed in small spaces. Both dD and dT electronic neutron generators (ENG) were used to interrogate ammonium nitrate fuel oil (ANFO) and cocaine hydrochloride, and the detector response of NaI, CsI, and LaBr3 were compared. The effect of tungsten shielding on the neutron flux in the gamma ray detectors was investigated, while carbon, beryllium, and polyethylene ENG moderator materials were optimized by determining the reaction rate density in the threats. In order to benchmark the modeling results, experimental measurements are compared with MCNPX simulations. In addition, the efficiency and die-away time of a portable differential die-away analysis (DDAA) detector using 3He proportional counters for SNM detection has been determined. View full abstract»

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  • The Gamma-Ray Imaging Framework

    Publication Year: 2013 , Page(s): 528 - 532
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (731 KB) |  | HTML iconHTML  

    The Gamma-Ray Imaging Framework (GRIF) is an open source (LGPL) software framework for creating real-time gamma-ray imaging applications. GRIF is written in C++ using Qt, and uses ROOT and the Boost Graph Library. GRIF provides automatic multi-threading and data management to make it easy to quickly develop power gamma-ray imagining applications. The model for application developers is built around the separation of data acquisition (DAQ) and analysis units. Users are expected to use the APIs for the DAQ and analysis units to build their applications. Memory and data are managed by GRIF, so the user does not need to worry about allocating and de-allocating memory for data or thread management and locking schemes. The user only needs to post data to and read data from the GRIF memory manager. GRIF uses XML configuration files for determining data dependences between DAQ and analysis units in the system. We will give an overview of the first release of GRIF, as well as show example applications that have been built using the framework. View full abstract»

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  • Simulations of Multi-Gamma Coincidences From Neutron-Induced Fission in Special Nuclear Materials

    Publication Year: 2013 , Page(s): 533 - 538
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1578 KB) |  | HTML iconHTML  

    A study is presented on the detection of illicit special nuclear materials (SNM) in cargo containers using a conceptual neutron-based inspection system with xenon-doped liquefied argon (LAr(Xe)) scintillation detectors for coincidence gamma-ray detection. For robustness, the system is envisioned to exploit all fission signatures, namely both prompt and delayed neutron and gamma emissions from fission reactions induced in SNM. However, this paper focuses exclusively on the analysis of the prompt gamma ray emissions. The inspection system probes a container using neutrons produced either by (d, D) or (d, T) in pulsed form or from an associated particle neutron generator to exploit the associated particle imaging (API) technique, thereby achieving background reduction and imaging. Simulated signal and background estimates were obtained in MCNPX (2.7) for a 2 kg sphere of enriched uranium positioned at the center of a 1m × 1m × 1m container, which is filled uniformly with wood or iron cargos at 0.1 g/cc or 0.4 g/cc. Detection time estimates are reported assuming probabilities of detection of 95% and false alarm of 0.5%. View full abstract»

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  • Assaying Used Nuclear Fuel Assemblies Using Lead Slowing-Down Spectroscopy and Singular Value Decomposition

    Publication Year: 2013 , Page(s): 539 - 544
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1096 KB) |  | HTML iconHTML  

    This study investigates the use of a Lead Slowing-Down Spectrometer (LSDS) for the direct and independent measurement of fissile isotopes in light-water nuclear reactor fuel assemblies. The current study applies MCNPX, a Monte Carlo radiation transport code, to simulate the measurement of the assay of the used nuclear fuel assemblies in the LSDS. An empirical model has been developed based on the calibration of the LSDS to responses generated from the simulated assay of six well-characterized fuel assemblies. The effects of self-shielding are taken into account by using empirical basis vectors calculated from the singular value decomposition (SVD) of a matrix containing the self-shielding functions from the assay of assemblies in the calibration set. The performance of the empirical algorithm was tested on version 1 of the Next-Generation Safeguards Initiative (NGSI) used fuel library consisting of 64 assemblies, as well as a set of 27 diversion assemblies, both of which were developed by Los Alamos National Laboratory. The potential for direct and independent assay of the sum of the masses of Pu-239 and Pu-241 to within 2%, on average, has been demonstrated. View full abstract»

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  • FREYA—A New Monte Carlo Code for Improved Modeling of Fission Chains

    Publication Year: 2013 , Page(s): 545 - 549
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (784 KB) |  | HTML iconHTML  

    A new simulation capability for modeling individual fission events and chains and the transport of fission products in materials is presented. The fission yield event yield algorithm (FREYA) is a Monte Carlo code for generating fission events providing correlated kinematic information for prompt neutrons, gammas, and fragments. For each fission event, FREYA generates multiplicity, energy, and the direction of neutrons and gammas while conserving energy and momentum at each step. To study materials with multiplication, shielding effects, and detectors, we have integrated FREYA into the general-purpose Monte Carlo code MCNP. This new tool will allow more accurate modeling of detector responses including correlations and the development of SNM detectors with increased sensitivity. View full abstract»

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  • Study on Background Gamma-Ray Reduction Using a Compton Backscattering Coincidence Technique

    Publication Year: 2013 , Page(s): 550 - 554
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (545 KB) |  | HTML iconHTML  

    We proposed a Compton Backscattering Coincidence (CBC) Technique to reduce background gamma-rays. Properties of the CBC technique were investigated with the EGS5 Monte Carlo simulation code and basic experiments. In this method, a sensitive area can be confined between two detectors while in a conventional method a sensitive area can't be confined because the sensitivity decreases as the solid angle decreases. Two detector configurations using two LaBr3 scintillators or HPGe-pure CaF2 scintillators were tested to validate the feasibility of the proposed technique. View full abstract»

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  • Effective Atomic Number of Ge-Doped and Al-Doped Optical Fibers for Radiation Dosimetry Purposes

    Publication Year: 2013 , Page(s): 555 - 559
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (505 KB) |  | HTML iconHTML  

    Optical fibers have been demonstrated by this group to show promising thermoluminescence (TL) properties with respect to ionizing radiation. Present research has focused on commercially produced single-mode telecommunication optical fibers manufactured by CorActive (Canada) either in the form of SiO2 optical fibers doped with either Ge or Al. Control of radiation dose is essential in performing an experiment in a biomedical context. One important aspect in this is the tissue equivalence of the dosimetric material. Mixtures or compounds that are similar in their radiation interaction characteristics to the soft tissue, bone or any other body constituents can be identified for this purpose. Effective atomic number of a medium prescribes its detection efficiency and tissue equivalence. To obtain the effective atomic number of the doped fibers, SEM (Scanning Electron Microscope) and EDXRS (Energy Dispersive X-ray Spectroscopy) analysis was performed to acquire the composition of the element inside the optical fibers. From our investigation, the value of Zeff is in the range of 11.5-13.4 and 11.7-13.7 for Ge-doped and Al-doped respectively (value of Zeff in soft tissue is 7.5 and Zeff for bone is between 11.6-13.8). Given that Ge- and Al-doped optical fibers are not soft-tissue equivalent, the assessment of dose deposition in such media would need to be corrected for an expected over-response. However, the value of Zeff is within the range of bone, making the optical fiber a strong candidate for use in skeletal radiation dosimetry. View full abstract»

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  • Verification on the Dose Profile Variation of a 3-D—NIPAM Polymer Gel Dosimeter

    Publication Year: 2013 , Page(s): 560 - 565
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (877 KB) |  | HTML iconHTML  

    A gel dosimeter is a three-dimensional (3-D) device that is used in radiotherapy. It is more efficient than traditional one-dimensional and two-dimensional dosimeters because it can be used in complicated radiation therapy applications. However, the achievement of temporal and spatial stabilities for gel dosimeters remains challenging in clinical applications because the fabrication process affects the polymerization reaction during irradiation. This study investigated the dose profile variation of an N-isopropyl acrylamide (NIPAM) polymer gel dosimeter by using the 3-D optical computed tomography scanner OCTOPUSTM 10X (MGS Research Inc.). Two acrylic containers (diameter=10, height=10, and diameter=15, height=15cm ) filled with polymer gel (gelatin: 5%, NIPAM: 5%, Bis: 3%, THPC: 5 mM) were irradiated by using intensity-modulated radiotherapy (SIEMENS Oncor Impression, 6 MV Photo beam). The treatment field was a 3 cm 3 cm square field, and the prescribed dose was 5 Gy. The results of the reconstruction line profile showed that the uncertainty of non-irradiated gel is less than 1.3% when a container with 10 cm diameters cooled in a refrigerator with a water bath. The maximum uncertainties of the irradiated gel at 24 h, 48 h, and 72 h post-irradiation were 2.9%, 2.9%, and 3.1%, respectively. However, the maximum uncertainty of the non-irradiated gel dosimeter increased to 3% when a container with 15 cm diameter was cooled in the same refrigerator. After irradiation, the maximum uncertainties of the irradiated gel at 24 h, 48 h, and 72 h post-irradiation were 13.1%, 13.7%, and 12.95%, respectively. The uncertainty differences for gels at different container sizes were attributed to the different cooling rates that were applied to the gels. The time required for large gel containers to cool in the refrigerator was more than 10 h, whereas the cooling process only took 4.2 h for gels in a small container. The time difference produced different temperature hist- ries for gels and may result in changes in gel sensitivity. Given the thermally induced pre-radiation polymerization, the time difference resulted in a deviation in dose profiles. This study reports that thermal control during gel preparation should be carefully performed for clinical applications to achieve a more accurate dose distribution in 3-D image reconstruction. View full abstract»

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  • Characterization of Tissue-Equivalent Materials Through Measurements of the Linear Attenuation Coefficient and Scattering Profiles Obtained With Polyenergetic Beams

    Publication Year: 2013 , Page(s): 566 - 571
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (846 KB) |  | HTML iconHTML  

    In this work seven tissue-equivalent materials (Nylon, Polyacetate, Polymethylmethacrylate (PMMA), water, muscle-equivalent, bone-equivalent and adipose-equivalent) were characterized, through their attenuation (linear attenuation coefficient) and scattering (scattering profile) properties. An energy dispersive X-ray system (EDXS) was used to analyze these properties simultaneously. The EDXS consisted of a tungsten anode X-ray tube operating at 60 kVp, a goniometer, and two detectors: a Cadmium Telluride (CdTe) detector, positioned at 7 degrees with relation to the incident beam, used for detecting the energy distribution of the scattered photons, and a Silicon Drift Detector (SDD), positioned at zero degree with relation to the incident beam, used for detecting the energy distribution of the transmitted beam (with the sample) or the incident beam (without the sample). The preliminary results obtained in this work show the potential of combining the linear attenuation coefficient and the scattering profile for characterizing and choosing the most suitable tissue-equivalent materials to simulate human tissue. Our results show that adipose-equivalent, water and bone-equivalent would be adequate to simulate adipose, muscle and bone tissue respectively. View full abstract»

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  • 8 and 10 MeV Electron Beams Small Field-Size Dosimetric Parameters Through the Fricke Xylenol Gel Dosimeter

    Publication Year: 2013 , Page(s): 572 - 577
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (904 KB) |  | HTML iconHTML  

    When small field sizes are recommended in radiotherapy, the dosimeter must have an adequate spatial resolution in order to determine the absorbed dose at the region of interest. The study of electron small field size is important since its dosimetry is not commonly performed in the clinical routine. It was verified that the Fricke Xylenol Gel (FXG) chemical dosimeter, with an effective atomic number of 7.75 and density of 1.05 g/cm3, presents adequate spatial resolution for absorbed dose distribution measurements, when small field sizes (square and circular) for 8 and 10 MeV electron beams are considered. The absorbed dose values are proportional to the absorbance spectrophotometric measurements that are proportional to the concentration of Fe+3 and the xylenol orange (XO) dye complex produced in the gel. The FXG behavior, for small field sizes irradiated with electron beams, was compared with those obtained using a small ionization chamber (IC). In this study, dosimetric parameters, such as beam profile, output factor, and percentage depth dose were evaluated. Since the dosimeter results showed no significant differences and the IC is considered the standard reference dosimeter by radiotherapy protocols, the FXG was validated for dosimetric parameter measurements to small field-size electron-beam irradiations. View full abstract»

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  • High Resolution Photon Counting With MCP-Timepix Quad Parallel Readout Operating at > 1~{\rm KHz} Frame Rates

    Publication Year: 2013 , Page(s): 578 - 585
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2964 KB) |  | HTML iconHTML  

    The unique capability of microchannel plates (MCPs) to convert a single photon/ electron/ ion/ neutron into a charge of 104 -107 electrons localized within 4-12 μm from the event position is widely used in event counting imaging detectors. The high spatial and timing resolution of MCP detectors have been demonstrated with different readout techniques. A compromise between the spatial and temporal resolution, the global/local counting rate and active area must always be made for each detector application. In this paper we present a 28 × 28 mm2 MCP detector with 2 × 2 Timepix ASICs for readout, capable of ~ 10 μm spatial resolution at event rates up to ~ 3 MHz, and in excess of 200 MHz with ~ 55 μm pixels. This detector has a unique capability to detect multiple simultaneous events, up to several thousand with ~ 10 μm resolution and > 25000 for the 55 μm mode. The latter is enabled by the new fast readout electronics capable of readout speeds of ~ 1200 frames/sec. Despite its limitations (relatively small active area, readout dead time of 300 μs) the MCP-Timepix detector can be very attractive for applications where high spatial resolution needs to be preserved for nearly simultaneous events, e.g., time of flight measurements with pulsed sources. The low noise of the Timepix readout enables operation at gains as low as 104 -105, which should extend the lifetime of the MCP detectors operating at high counting rates. View full abstract»

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  • Design and Evaluation of an SOI Pixel Sensor for Trigger-Driven X-Ray Readout

    Publication Year: 2013 , Page(s): 586 - 591
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1369 KB) |  | HTML iconHTML  

    We have been developing a monolithic active pixel sensor with the silicon-on-insulator (SOI) CMOS technology for use in future X-ray astronomical satellite missions. This sensor is called XRPIX. Our objective is to replace the X-ray CCD, which is currently the standard detector in the field, with the developed XRPIX, which offers high coincidence time resolution (~ 50 ns), superior hit-position readout time (~ 10 μs), and wide bandpass (0.5-40 keV), in addition to having comparable performance in terms of imaging spectroscopy. In our previous study, we built a prototype sensor called XRPIX1 and confirmed its basic X-ray imaging spectroscopy performance in a mode that read out the entire area (all pixels). The next step is to realize a high-speed, intelligent readout for X-ray detection. XRPIX1 comprises a trigger circuit for each pixel, so as to detect an X-ray photon injection; this system is capable of direct access to selected pixels to read out the signal amplitude. We describe the design of the trigger circuitry system and report on the first resolved X-ray spectra obtained in the trigger-driven readout mode. View full abstract»

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  • Simulation Study of Resistor Networks Applied to an Array of 256 SiPMs

    Publication Year: 2013 , Page(s): 592 - 598
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (917 KB) |  | HTML iconHTML  

    In this work we describe a procedure to reduce the number of signals detected by an array of 256 Silicon Photomultipliers (SiPMs) using a resistor network to divide the signal charge into few readout channels. Several configurations were modeled, and the pulsed signal at the readout contacts were simulated. These simulation results were experimentally tested on a specifically designed and manufactured set of printed circuit boards. Three network configurations were modeled. The modeling provided encouraging results for all three configurations. The measurements on the prototypes constructed for this study, however, provided useful position-sensitivity for only one of the network configurations. The lack of input signal amplification into the networks, the SiPM dark current, as well as the complexity of an eight layers board with parasitic capacitances, could have caused the degradation of resolving the impact photon position. This is hard to overcome with external printed circuit boards and components. View full abstract»

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  • Evaluation of Multi-Channel ADCs for Gamma-Ray Spectroscopy

    Publication Year: 2013 , Page(s): 599 - 605
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1747 KB) |  | HTML iconHTML  

    As nuclear physicists increasingly design large scale experiments with hundreds or thousands of detector channels, there are growing needs for high density readout electronics with good timing and energy resolution that at the same time offer lower cost per channel compared to existing commercial solutions. Recent improvements in the design of commercial analog to digital converters (ADCs) have resulted in a variety of multi-channel ADCs that are natural choice for designing such high density readout modules. However, multi-channel ADCs typically are designed for medical imaging/ultrasound applications and therefore are not rated for their spectroscopic characteristics. In this work, we evaluated the gamma-ray spectroscopic performance of several multi-channel ADCs, including their energy resolution, nonlinearity, and timing resolution. Some of these ADCs demonstrated excellent energy resolution, 2.66% FWHM at 662 keV with a LaBr3 or 1.78 keV FWHM at 1332.5 keV with a high purity germanium (HPGe) detector, and sub-nanosecond timing resolution with LaBr 3. We present results from these measurements to illustrate their suitability for gamma-ray spectroscopy. View full abstract»

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  • A Novel Technique for the Stabilization of SiPM Gain Against Temperature Variations

    Publication Year: 2013 , Page(s): 606 - 611
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (657 KB) |  | HTML iconHTML  

    In several applications of Silicon Photo-Multipliers (SiPM), drifts of the detector gain with the temperature represent a severe drawback which prevents from achieving optimal performance. We propose an original technique to address this issue, based upon the use of a SiPM not exposed to the light as a temperature sensor. The average amplitude of the dark pulses produced by this detector is measured and controlled to a constant reference value by means of a negative feedback loop, which automatically varies the bias voltage of the SiPM. The same bias voltage variations generated by the feedback loop are also applied to the sensitive SiPMs used in the specific application, thus making constant their gain. The effectiveness of the proposed compensation scheme has been experimentally demonstrated by using two SiPMs from FBK-irst (1 mm × 1 mm, 400 micro-cells, breakdown voltage Vbr ≅ 29 V), one as temperature sensor involved in the negative feedback loop and the other as light sensitive device. Both detectors have been enclosed in a thermally isolated box with temperature varied in the interval between 20 °C and 30 °C : the variation of the SiPM gain can be reduced from more than 20%, without compensation, to about 2%. View full abstract»

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IEEE Transactions on Nuclear Science focuses on all aspects of the theory and applications of nuclear science and engineering, including instrumentation for the detection and measurement of ionizing radiation; particle accelerators and their controls; nuclear medicine and its application; effects of radiation on materials, components, and systems; reactor instrumentation and controls; and measurement of radiation in space.

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