ALBERT

Description: Programming languages like C and Ada combined with proprietary embedded operating systems have dominated the real-time application space for decades. The new C++11 standard includes native, language-level support for concurrency, a required feature for any nontrivial event-oriented real-time software. Threads, Locks, and Atomics now exist to provide the necessary tools to build the structures that make up the foundation of a complex real-time system. The National Spherical Torus Experiment Upgrade (NSTX-U) at the Princeton Plasma Physics Laboratory (PPPL) is breaking new ground with the language as applied to the needs of fusion devices. A new Digital Coil Protection System (DCPS) will serve as the main protection mechanism for the magnetic coils, and it is written entirely in C++11 running on Concurrent Computer Corporation’s real-time operating system, RedHawk Linux. It runs over 600 algorithms in a 5 kHz control loop that determine whether or not to shut down operations before physical damage occurs. To accomplish this, NSTX-U engineers developed software tools that do not currently exist elsewhere, including real-time atomic synchronization, real-time containers, and a real-time logging framework. Together with a recent (and carefully configured) version of the GCC compiler, these tools enable data acquisition, processing, and output using a conventional operating system to meet a hard real-time deadline (that is, missing one periodic is a failure) of 200 microseconds.

Description: Thallium-bromide (TlBr) is currently under investigation as an alternative room-temperature semiconductor gamma-ray spectrometer due to its favorable material properties (large bandgap, high atomic numbers, and high density). Previous work has shown that 5 mm thick pixelated TlBr detectors can achieve sub-1% FWHM energy resolution at 662 keV for single-pixel events. These results are limited to $ - 20{^ circ }{rm C}$ operation where detector performance is stable. During the first one to five days of applied bias at $ - 20{^ circ }{rm C}$ , many TlBr detectors undergo a conditioning phase, where the energy resolution improves and the depth-dependent electron drift velocity stabilizes. In this work, the spectroscopic performance, drift velocity, and freed electron concentrations of multiple 5 mm thick pixelated TlBr detectors are monitored throughout the conditioning phase. Additionally, conditioning is performed twice on the same detector at different times to show that improvement mechanisms relax when the detector is stored without bias. We conclude that the improved spectroscopy results from internal electric field stabilization and uniformity caused by fewer trapped electrons.

Description: Silicon Photomultipliers (SiPMs) are attractive candidates for light detectors for next generation liquid xenon double-beta decay experiments, like nEXO (next Enriched Xenon Observatory). In this paper we discuss the requirements that the SiPMs must satisfy in order to be suitable for nEXO and similar experiments, describe the two test setups operated by the nEXO collaboration, and present the results of characterization of SiPMs from several vendors. In particular, we find that the photon detection efficiency at the peak of xenon scintillation light emission (175-178 nm) approaches the nEXO requirements for tested FBK and Hamamatsu devices. Additionally, the nEXO collaboration performed radio-assay of several grams of bare FBK devices using neutron activation analysis, indicating levels of $^{40}{rm K}$ , $^{232}{rm Th}$ , and $^{238}{rm U}$ of the order of $ 〈 0.15$ , ( $ 6.9cdot 10^{ - 4} - 1.3 cdot 10^{ - 2}$ ), and $ 〈 0.11 ~hbox{mBq}/hbox{kg}$ , respectively.

Description: It is very important for plant operators to be informed of the departure from nucleate boiling ratio (DNBR) to prevent the fuel cladding from melting and a boiling crisis in a nuclear reactor. The reactor core monitoring and protection systems require a minimum DNBR value to monitor reactor coolant conditions. In this study, in order to estimate the minimum DNBR value, a cascaded fuzzy neural network (CFNN) method was used. The CFNN model can be used to estimate the minimum DNBR value through the process of adding fuzzy neural networks (FNNs) repeatedly. The proposed DNBR estimation algorithm was verified by applying the nuclear and thermal data acquired from many numerical simulations of the optimized power reactor 1000 (OPR1000). The CFNN model was compared to previously developed models and was found to be superior to them. Therefore, this model can be used to effectively monitor and predict the minimum DNBR in the reactor core.

Description: A program was started in 1999 in the Portuguese Research Reactor to test electronics components and circuits for the LHC facility at CERN, initially with a dedicated in-pool irradiation container used at a reactor power of 2 kW and later an irradiation chamber outside the pool, with tailored neutron and gamma filters that could be used at 1 MW. Practice has shown the need to introduce several improvements to the irradiation procedures and infrastructures over the years. In this paper, we review the lessons learned and the major improvements introduced.

Description: During irradiation UO 2 nuclear fuel experiences the development of a non-uniform distribution of porosity which contributes to establish varying mechanical properties along the radius of the pellet. Radial variations of both porosity and elastic properties in high burnup UO 2 pellet can be investigated via high frequency acoustic microscopy. For this purpose ultrasound waves are generated by a piezoelectric transducer and focused on the sample, after having travelled through a coupling liquid. The elastic properties of the material are related to the velocity of the generated Rayleigh surface wave ( $ mathrm {V}_{ mathrm {R}}$ ). A UO 2 pellet with a burnup of 67 GWd/tU was characterized using the acoustic microscope installed in the hot cells of the JRC-ITU at a 90 MHz frequency, with methanol as coupling liquid. $ mathrm {V}_{ mathrm {R}}$ was measured at different radial positions. A good agreement was found, when comparing the porosity values obtained via acoustic microscopy with those determined using SEM image analysis, especially in the areas close to the centre. In addition, Young’s modulus was calculated and its radial profile was correlated to the corresponding burnup profile and to the hardness radial profile data obtained by Vickers micro-indentation

Description: In the framework of the European I-Smart project, optimal 4H-SiC based diode geometries were developed for high temperature neutron detection. Irradiation tests were conducted with 14 MeV fast neutrons supplied by a deuterium-tritium neutron generator with an average neutron yield of $4.04 times {10^{10}} - 5.25 times {10^{10}};hbox{n/s}$ at Neutron Laboratory of the Technical University of Dresden in Germany. In this paper, we interpret the first measurements and results with 4H-SiC detector irradiated with fast neutrons from room temperature up to 500 °C. These experiments are serving also the first simulation of the harsh environmental condition measurements in the tritium breeding blanket of the ITER fusion reactor, which is one of the most prominent planned location of high temperature neutron flux characterization studies in the near future.

Description: A proposal for an autonomous and flexible ship container inspection system is presented. This could be accomplished by the incorporation of an inspection system on various container transportation devices (straddle carriers, yard gentry cranes, automated guided vehicles, trailers). The configuration is terminal specific and it should be defined by the container terminal operator. This enables that no part of the port operational area is used for inspection. The inspection scenario includes container transfer from ship to transportation device with the inspection unit mounted on it. The inspection is performed during actual container movement to the container location. A neutron generator without associated alpha particle detection is used. This allows the use of higher neutron intensities ( $5times {10^9} - {10^{10}} text{n/s}$ in $4pi $ ). The inspected container is stationary in the “inspection position” on the transportation device while the “inspection unit” moves along its side. The following analytical methods will be used simultaneously: neutron radiography, X-ray radiography, neutron activation analysis, (n, $gamma $ ) and (n,n’ $gamma $ ) reactions, neutron absorption. and scattering, X-ray backscattering. The neutron techniques will utilize “smart collimators” for neutrons and gamma rays, both emitted and detected. The inspected voxel is defined by the intersection of the neutron generator and the detectors solid angles. The container inspection protocol is based on identification of discrepancies between the cargo manifest, elemental “fingerprint” and radiography profiles. In addition, the information on contain- r weight is obtained during the container transport and screening by measuring of density of material in the container.

Description: It was demonstrated in the previous work that various threat materials could be detected inside the sea going cargo container by measuring the three variables, carbon and oxygen concentration and density of investigated material. Density was determined by measuring transmitted neutrons, which is not always practical in terms of setting up the instrument geometry. In order to enable more geometry flexibility, we have investigated the possibility of using the scattered neutrons in cargo material identification. For that purpose, the densities of different materials were measured depending on the position of neutron detectors and neutron generator with respect to the target position. One neutron detector was put above the target, one behind and one in front of the target, above the neutron generator. It was shown that all three positions of neutron detectors can be successfully used to measure the target density, but only if the detected neutrons are successfully discriminated from the gamma rays.

Description: Determination of photon heating by calculation is an important issue for the Jules Horowitz Reactor (JHR), the next international Material-Testing Reactor (MTR) under construction at the CEA Cadarache research center in the south of France. Accurate knowledge of photon heating in structure materials and irradiation devices is necessary for JHR design and safety studies. In this paper, we quantify the impact of different photon-heating calculation routes by comparing absorbed dose and Kinetic Energy Released per MAss (KERMA) calculations from two different Monte Carlo codes, TRIPOLI-4.9 and Monte Carlo N-Particle transport code (MCNP). These calculations are carried out in JHR-representative geometries with the nuclear-data library JEFF3.1.1 and the photon-data library EPDL97. Discrepancies amounting to up to 18% between absorbed dose and KERMA are found in JHR irradiation devices and are linked to charged-particle transport effects taking place in heterogeneous materials of small dimensions. In a JHR-assembly cell, discrepancies of about 1% on photon KERMA and of about 3% on absorbed dose are highlighted between the two Monte Carlo codes. These latter discrepancies are small compared to typical sources of uncertainty for Monte Carlo calculation (for instance, nuclear data uncertainty) and are supposed to be due to differences in the processing of gamma-production data by neutron interactions and to differences in electromagnetic-shower models and implementation between the two codes.

Description: Plastic scintillator loading with gadolinium-rich organometallic complexes shows a high potential for the deployment of efficient and cost-effective neutron detectors. Due to the low-energy photon and electron signature of thermal neutron capture by Gd-155 and Gd-157, alternative treatment to pulse-shape discrimination has to be proposed in order to display a count rate. This paper discloses the principle of a compensation method applied to a two-scintillator system: a detection scintillator interacts with photon and fast neutron radiation and is loaded with gadolinium organometallic compound to become a thermal neutron absorber, while a not-gadolinium loaded compensation scintillator solely interacts with the fast neutron and photon part of incident radiation. After the nonlinear smoothing of the counting signals, a hypothesis test determines whether the resulting count rate post-background response compensation falls into statistical fluctuations or provides a robust indication of neutron activity. Laboratory samples are tested under both photon and neutron irradiations, allowing the authors to investigate the performance of the overall detection system in terms of sensitivity and detection limits, especially with regards to a similar-active volume He-3 based commercial counter. The study reveals satisfactory figures of merit in terms of sensitivity and directs future investigation toward promising paths.

Description: This paper presents a new code for the analysis of gamma spectra generated by an equipment for continuous measurement of gamma radioactivity in aerosols with paper filter. It is called pGamma and has been developed by the Nuclear Engineering Research Group at the Technical University of Catalonia - Barcelona Tech and by Raditel Serveis i Subministraments Tecnològics, Ltd. The code has been developed to identify the gamma emitters and to determine their activity concentration. It generates alarms depending on the activity of the emitters and elaborates reports. Therefore it includes a library with NORM and artificial emitters of interest. The code is being adapted to the monitors of the Environmental Radiological Surveillance Network of the local Catalan Government in Spain (Generalitat de Catalunya) and is used at three stations of the Network.

Description: Prosthetics treatments with total or partial reconstruction are highly recommended in order to investigate caries, fractures and for better aesthetic. The purpose of this study was to evaluated marginal and internal fit of infrastructures (ceramic and metal) by using a high resolution X-ray micro-computed tomography. Each framework was placed on the original model and scanned. Image processing analysis and statistical approaches were combined together to evaluated directly in 3D the gap between the crown and the dental, which makes it possible to have a realistic dental arcade model.

Description: Latest Fusion energy experiments envisage a quasi-continuous operation regime. In consequence, the largest experimental devices, currently in development, specify high-availability (HA) requirements for the whole plant infrastructure. Highly available systems operate seamlessly in the case of component failure, ensuring safety of equipment, people, environment and investment. Control and Data Acquisition (C&DA) systems for Fusion diagnostics are considered mission-critical and require high degrees of availability. IPFN developed a C&DA system for fast control of advanced Fusion devices, targeting HA. The hardware platform is based on in-house developed Advanced Telecommunication Computing Architecture (ATCA) instrumentation modules–digitizing and data switch blades using PCI Express (PCIe) over the ATCA backplane Fabric Channel Interface, connecting to an external PCIe host computer. At the hardware management level, the system architecture takes advantage of ATCA’s HA characteristics, such as its redundant hardware components, redundant backplane topologies and Field Replaceable Unit (FRU) “Hot Swap”. At the software level, PCIe supports “Hot Plug” graceful device insertion and removal. The implementation of PCIe Hot Plug for the ATCA form-factor is one of the major tasks involved and a solution for such implementation was also developed. The paper describes how IPFN C&DA system can be setup to take advantage of both ATCA and PCIe features to perform with the desired degree of availability, by implementing fail-over mechanisms based on the use of redundancy, thus being suitable for advanced C&DA systems in Fusion.

Description: The time response of a recently developed polysiloxane based liquid scintillator has been analyzed for the first time: a special focus on the pulse shape discrimination capability of this material, which is characterized by low toxicity and low volatility, has been addressed. Fluorescence lifetime and scintillation pulses have been studied at different primary dye concentrations, with the aim of optimizing the neutron/gamma discrimination, connecting the results to the energy transfer and to the formation of excimers inside the scintillating solution. Pulse shape analysis performed during the irradiation of the samples with a pulsed neutron beam allowed the definition of a figure of merit as an indicative parameter for the neutron/gamma discrimination. The dependence of this parameter from radiation energy and PPO concentration has been analyzed in order to optimize the performances of the material in view of its possible use in environments with high gamma-ray radiation background.

Description: The measurement of fusion power, i.e., total neutron emissivity, will play an important role for achieving the goals of ITER project, in particular the fusion gain factor Q related to the reactor performance. The article gives overview of the neutron diagnostics being developed for ITER. Particular attention is given also to the development of the neutron calibration strategy whose main scope is to achieve the required accuracy of 10% for the measurement of fusion power. Neutron Flux Monitors located in diagnostic ports and inside the vacuum vessel will measure ITER total neutron emissivity, expected to range from $10^{14}~mathrm {n}/mathrm {s}$ in Deuterium—Deuterium (DD) plasmas up to almost $10^{21}~mathrm {n}/mathrm {s}$ in DT plasmas. The neutron detection systems as well all other ITER diagnostics have to withstand high nuclear radiation and electromagnetic fields as well ultrahigh vacuum and thermal loads.

Description: This paper describes the development and testing of a neutron counter, spectrometer, and dosimeter that is compact, efficient, and accurate. The 1.3 liter detector head for this instrument is a composite detector with an organic scintillator containing uniformly distributed 6 Li 6 nat Gd 10 B 3 O 9 : Ce (LGB:Ce) microcrystals. Moderating neutrons that have slowed sufficiently in the plastic, capture in one of the Lithium-6, Boron-10, or Gadolinium-157/155 atoms in the LGB:Ce scintillator, which then releases the capture energy in a characteristic cerium emission pulse. The measured captured pulses indicate the presence of neutrons. When a scintillating fluor is present in the plastic, the light pulse resulting from the neutron moderating in the plastic is paired with the LGB:Ce capture pulse to identify the energy of the neutron. This data was used to assist in the unfolding of the neutron spectra. The unfolded spectra were then validated with known spectra, at both neutron emitting isotopes and fission/accelerator facilities, Los Alamos Neutron Science Center (LANSCE), Edwards Accelerator Laboratory (EAL) at Ohio University. The instrument can measure neutrons and their spectra over the range between 0.8 MeV and 150 MeV with an average uncertainty in neutron rate of only ±8%.

Description: Basic concepts and the development of a high counting rate digital spectrometry system based on efficient ADCs and latest available FPGA are presented with the aim of using such a system, coupled to fast scintillators, in plasma experiments. The prototype system is a 1 channel 12-bit 1 GSPS digitizer with $2~mathrm {V}_{mathrm {pp}}$ input voltage. Preliminary results tested with different radioactive sources are shown for low (0.03 Mcps) and high (2.2 Mcps) counting rates. A comparison of energy spectra and energy resolution with what obtained by a commercial device is also shown.

Description: The nuclear radiation energy deposition rate (unit usually employed: $mathrm {W.g}^{-1}$ ) is a key parameter for the thermal design of experiments on materials and nuclear fuel carried out in experimental channels of irradiation reactors, such as the French reactor in Saclay called OSIRIS or the Polish reactor named MARIA. In particular the quantification of nuclear heating allows the prediction of heat and thermal conditions induced in irradiated devices and/or structural materials. Various sensors are used to quantify this parameter, in particular radiometric calorimeters, also known as in-pile calorimeters. Two main kinds of in-pile calorimeter exist possessing two geometries and two measurement principles: the single-cell calorimeter and the differential calorimeter. The present work focuses on specific examples of these calorimeter types, from the step of their out-of-pile calibration (transient and steady experiments respectively) to the comparison between numerical and experimental results obtained from two irradiation campaigns (French and Polish reactors). The main aim of this paper is to propose a steady numerical approach to estimate the single-cell calorimeter response under irradiation conditions.

Description: In the perspective of reducing ITER risks, JET next DT campaign presents a unique potential, since the device can combine the right first wall material mix, the reactor fuel mixture and sufficient dimensions and fields to confine the alpha particles. An integrated diagnostic programme, to maximize the scientific output of this DT campaign, is under way and concentrates mainly on the diagnostic for the fusion products, on advanced measurements for instabilities and on testing diagnostic technologies in a 14 MeV neutron environment.

Description: In this paper, the overvoltage protection module (OVP) for the power supply (PS) system of the Belle II pixel detector (PXD) is described. The aim of the OVP is to protect the detector and associated electronics against overvoltage conditions. These include failures of the PS itself, wrong settings of the output voltages, and also transients coming out of a noisy environment of the experiment. The OVP system works independently of any other protection of the PS system, increasing its overall reliability.

Description: In recent years there has been a growing interest to use reconfigurable modules, based on field-programmable gate array (FPGA) devices, in nuclear environments. One of the requirements for these types of modules, when operating in complex future nuclear power experiments, is their remote update capability. The operational needs of pulsed fusion reactors will lead to a large production of very high energy neutrons (MeV range). The current procurement policies for nuclear installations do not allow exposure of electronics to radiation, except following very strict rules. However, considering the “as low as (is) reasonably achievable” (ALARA) principle with respect to human exposure to radiation, the access to cubicles might be restricted, requiring the remote update of FPGA codes. FPGAs are volatile devices, and their programming code is usually stored in dedicated flash memories for proper configuration during module power-on. This paper presents an alternative method for FPGA remote update, capable to store new FPGA codes in inboard Serial Peripheral Interface (SPI) flash memories. The new method, based on the Xilinx Quick Boot application note and adapted to PCIe protocol, was developed with the KC705 Evaluation Kit from Xilinx and successfully tested in the in-house Advanced Mezzanine Card (AMC) prototype, installed on the ATCA-PTSW-AMC4 carrier module from the ITER Fast Plant System Controller catalogue.

Description: Environmental scientific research requires a detector that has sensitivity low enough to reveal the radiological content for the presence of potential contaminants in the sample at a reasonable counting time. CANBERRA developed a germanium detector geometry called Small Anode Germanium (SAGe) Well detector. The SAGe Well detector is a new type of low capacitance device manufactured using small anode technology capable of advancing many environmental scientific research applications. The performance of this detector has been evaluated for a range of sample sizes and geometries counted inside the well, and on the end cap of the detector. The detector has energy resolution performance similar to semi-planar detectors, and offers significant improvement over the existing coaxial and Well detectors. Energy resolution performance of 750 eV Full Width at Half Maximum (FWHM) at 122 keV $gamma$ -ray energy and resolution of 2.0–2.3 keV FWHM at 1332 keV $gamma$ -ray energy are guaranteed for detector volumes up to $425 ~hbox{cm}^{3}$ . The SAGe Well detector offers an optional 28 mm well diameter with the same energy resolution performance as the standard 16 mm well. Such outstanding performance will benefit environmental applications in revealing the detailed radionuclide content of samples, particularly at low energy. The detector is compatible with electric coolers without any sacrifice in performance and supports the CANBERRA Mathematical efficiency calibration method (In situ Object Calibration Software or ISOCS, and Laboratory SOurceless Calibration Software or LabSOCS). In addition, the SAGe Well detector supports true coincidence summing available in the ISOCS/LabSOCS framework. The improved resolution performance of this new device gr- atly enhances its detection sensitivity for a range of sample sizes and geometries counted inside the well. This results in lower minimum detectable concentrations (MDC) compared to Traditional Well detectors. The SAGe Well detectors are compatible with Marinelli beakers and compete very well with semi-planar and coaxial detectors for large samples in many applications.

Description: Precision ultrasonic measurements in binary gas systems provide continuous real-time monitoring of mixture composition and flow. Using custom microcontroller-based electronics, we have developed sonar instruments, with numerous potential applications, capable of making continuous high-precision sound velocity measurements. The instrument measures sound transit times along two opposite directions aligned parallel to – or obliquely crossing – the gas flow. The difference between the two measured times yields the gas flow rate while their average gives the sound velocity, which can be compared with sound velocity vs. molar composition look-up curves to obtain the binary mixture at a given temperature and pressure. The look-up curves may be generated from prior measurements in known mixtures of the two components, from theoretical calculations, or from a combination of the two. We describe the instruments and their performance within numerous applications in the ATLAS experiment at the CERN Large Hadron Collider (LHC). The instruments can be of interest in other areas where continuous in-situ binary gas analysis and flowmetry are required.

Description: In the year 2011, a research project has started focus on building of a neutron radiography facility at the LVR-15 research reactor in Rez, Czech Republic. One of the unused horizontal channels was chosen to be adapted for this purpose. However, the original beam parameters having a high presence on fast neutrons which may damage the neutron detector, and gamma radiation which causes undesired background were unsuitable. The need for an intensive thermal neutron beam with a very low fast neutron ratio led to the decision of installing a thermal neutron filter into the channel tube. As the channel layout is very spatial limiting, a simple solution had to be chosen. Usually large single-crystal ingots of proper material parameters can be used as filters. Single-crystal silicon was chosen as the preferred filter material for its availability in sufficient dimensions and low production costs. Additionally to its ability to significantly reduce the ratio of fast neutrons in the beam, if the filter dimensions are large enough, it provides shielding against the reactor gamma radiation. For the calculation of the required beam dimensions the Monte-Carlo MCNP transport code was used. However, as the code does not include the neutron cross-section libraries for thermal neutron scattering on crystalline structures, the original silicon cross-section libraries had been manually modified using an approximated relation based on thermal neutron scattering theory. Carrying out a series of calculations the filter thickness of 1 m proved good for gaining a beam with desired parameters and a low gamma background. After mounting the filter inside the channel several measurements of the neutron field were realized at the beam exit. The results have justified the calculated values. After the successful filter installing and a series of measurements, first test neutron radiography attempts with chosen samples could been carried out.

Description: The paper presents first results from the Front-End Board (FEB) with the biggest Cyclone ® V E FPGA 5CEFA9F31I7N, supporting 8 channels sampled up to 250 MSps @ 14-bit resolution. Considered sampling for the planned upgrade of the Pierre Auger surface detector array is 120 MSps, however, the FEB has been developed with external anti-aliasing filters to keep a maximal flexibility. Six channels are targeted to the SD, two the rest for other experiments like: Auger Engineering Radio Array and additional muon counters. More channels and higher sampling generate larger size of registered events. We used the standard radio channel for a radio transmission from the detectors to the Central Data Acquisition Station (CDAS) to avoid at present a significant modification of a software in both sides: the detector and the CDAS (planned in a future for a final design). Several variants of the FPGA code were tested for 120, 160, 200 and even 240 MSps DAQ. Tests confirmed a stability and reliability of the FEB design in real pampas conditions with more than 40°C daily temperature variation and a strong sun exposition with a limited power budget only from a single solar panel. Seven FEBs have been deployed in a hexagon of test detectors on a dedicated Engineering Array.

Description: After bouncing back and forth between the countries of the “founding organizations” of the ANIMMA conference series, CEA in France and SCK•CEN in Belgium, ANIMMA 2015 was for the first time held in the Portuguese capital of Lisbon, following an invitation by the Instituto de Plasmas e Fusão Nuclear/Instituto Superior Técnico (IPFN/IST).

Description: The standard procedure for neutron reactor dosimetry is based on neutron irradiation of a target and its post-irradiation analysis by Gamma and/or X-ray spectrometry. Nowadays, the neutron spectra can be easily characterized for thermal and fast energies (respectively 0.025 eV and $ > 1~hbox{MeV}$ ). In this paper we propose a new target and an innovating post-irradiation technique of analysis in order to detect the neutron spectra within the energy of 1 keV to 1 MeV. This paper will present the calculations performed for the selection of a suitable nuclear reaction and isotope, the results predicted by simulations, the irradiation campaign that is proposed, and the post-irradiation technique of analysis.

Description: I am glad to be able to assist with the making of this special issue on ANIMMA 2015 again, and I would like to thank the organizers of the conference to have chosen the IEEE Transactions on Nuclear Science again for the collection of publication-grade material presented at the meeting. But I would also like to express my thanks to the Associate Editors that have conducted the peer-review process of all the manuscripts submitted in a highly professional manner. It is our goal to have every paper evaluated by at least three colleagues active in the field, and so the number of individuals that have contributed to this issue is high, again higher than in the previous years: not less than 459 colleagues have spent their valuable time by serving as reviewers for the material, whether they have attended the conference and submitted a manuscript themselves or not. It is the efficient and professional, though voluntary work, of our Associate Editors and reviewers that made this special issue become true.

Description: We are presenting a new approach to a filtering of radio frequency interference (RFI) in the Auger Engineering Radio Array (AERA), which studies the electromagnetic part of the extensive air showers. Radio stations can observe radio signals caused by coherent emissions due to geomagnetic radiation and charge excess processes. AERA observes the frequency band from 30 to 80 MHz. This range is highly contaminated by human-made RFI. In order to improve the signal to noise ratio RFI filters are used in AERA to suppress this contamination. The filter has already been tested with real AERA radio stations in the Argentinean Pampas with very successful results. The linear equations were solved either in the virtual soft-core NIOS® processor (implemented in the FPGA chip as a net of logic elements) or in the external Voipac PXA270M ARM processor. The NIOS® processor is relatively slow (50 MHz internal clock), and the calculations performed in an external processor consume a significant amount of time for data exchange between the FPGA and the processor. Tests showed very good efficiency of the RFI suppression for stationary (long-term) contaminations. However, we observed short-time contaminations, which could not be suppressed either by the IIR-notch filter or by the FIR filter based on the linear predictions. For the LP FIR filter, the refresh time of the filter coefficients was too long and the filter did not keep up with the changes in the contamination structure, mainly due to a long calculation time in a slow processors. We propose to use the Cyclone® V SE chip with an embedded micro-controller operating with a 925 MHz internal clock to significantly reduce the refreshment time of the FIR coefficients. First results in the laboratory are very promising.

Description: This paper reports on a numerical feasibility study of a passive neutron coincidence counting system for radioactive waste drums with plastic scintillators. The motivation is to replace $^{3}text{He}$ gas counters generally used for this type of measurement. Indeed, plastic scintillators present several advantages for the measurement of neutron coincidences such as a good efficiency for detecting fast neutrons, short detection time, and low cost comparatively to $^{3}text{He}$ . However, unlike $^{3}text{He}$ counters, their high sensitivity to gamma rays and cross talk constitutes a drawback as parasite random and true coincidences are detected together with the useful signal of plutonium. Simulations are performed using the Monte Carlo transport code MCNPX-PoliMi v2.0 coupled to data processing algorithms developed with ROOT data analysis software. Performances of the coincidence counting system are studied for the case of a vitrified waste drum containing Pu and $^{241}text{Am}$ , focusing particularly on multiplicity 1 and 2, i.e., 2 or 3 pulses recorded in a short time gate in different detectors. Cross talk induced by neutrons and gamma rays has been characterized in terms of time and distance between detectors, and strategies to limit this phenomenon are reported, consisting of ignoring neighboring detectors signal. A significant improvement of the Pu to $^{241}text{Am}$ ratio for multiplicity 2 coincidences has thus been obtained, at the expense of counting statistics. Alternative case studies with organic and metallic matrixes of technological wastes are also reported, for which the part of useful signal - f plutonium is significantly higher, showing the feasibility of the measurement method.

Description: In order to overcome the shortage of $^{3}mathrm {He}$ detectors for subcritical experiments in the IPEN/MB-01 reactor, some experiments were performed employing less sensitive detectors, such as BF 3 , and a logic input module, which sums the counts from different detectors. Through microscopic and macroscopic neutron noise technique, it was possible to obtain, respectively, Rossi- $alpha $ distribution and Auto Power Spectral Densities (APSD) for each detector configuration and various subcritical levels, and the prompt neutron decay constant ( $alpha $ ) was extracted through a least squares procedure. In addition, Cross Power Spectral Densities (CPSD) were acquired for different types of detectors and the correlation among those detectors was confirmed. It was also observed that there was no loss of correlation among the neutron pulses, and therefore, the CPSD curves demonstrated the presence of correlated events. The $alpha $ parameter was used as an indicator for the comparison of the results and for the quality of the experimental data. The obtained values demonstrate that the sum of counts technique does not present loss of information (correlated neutrons) even for different models and types of detectors, suggesting that the technique may be employed in neutron noise measurements for subcritical reactivity.

Description: Acoustic leak detection for steam generators of sodium fast reactors have been an active research topic since the early 1970s and several methods have been tested over the years. Inspired by its success in the field of automatic speech recognition, we here apply hidden Markov models (HMM) in combination with Gaussian mixture models (GMM) to the problem. To achieve this, we propose a new feature calculation scheme, based on the temporal evolution of the power spectral density (PSD) of the signal. Using acoustic signals recorded during steam/water injection experiments done at the Indira Gandhi Centre for Atomic Research (IGCAR), the proposed method is tested. We perform parametric studies on the HMM+GMM model size and demonstrate that the proposed method a) performs well without a priori knowledge of injection noise, b) can incorporate several noise models and c) has an output distribution that simplifies false alarm rate control.

Description: We propose an experimental methodology for the purpose of quantitative void fraction measurements in fourth generation Sodium cooled fast reactors with a standard Eddy Current Flow Meter (ECFM) sensor. The methodology consists of using the technique of ellipse fit and correlate the fluctuations in the angle of inclination of this ellipse with the void fraction. This methodology is applied in this paper to an ideal configuration of periodic grooves on solid aluminium cylinder with various volumic fractions. The effects of physical parameters such as coil excitation frequency, coil current and motion have been studied. The first results show that ECFM is sensitive to void fractions between 0.3% and 6.9%. It further demonstrates that the response to void fraction is insensitive to the mean velocity of the two-phase medium.

Description: This paper presents a novel front-end Application Specific Integrated Circuit (ASIC) dedicated to CZT detectors for positron-emission tomography (PET) imaging applications. The ASIC consists of a preamplifier using split-leg topology, a variable gain amplifier, a time-interleaved ramp ADC and a timing controller. The design techniques of these circuit blocks are discussed in detail. Meanwhile, the digital CR-RC shaping and the digital trapezoidal shaping are introduced as well. A prototype ASIC is implemented in CMOS $0.35~mu mathrm {m}$ process. The preliminary results have been obtained. The detection range of the gamma ray is from 11.2 keV to 550 keV. The non-linearity of the output voltage is less than 3%. The gain of the readout channel is 40.2 V/pC. The test results show that the proposed front-end electronics is appropriable for PET imaging applications.

Description: In this work we present the characterization of a large area $200~hbox{mm} times 200~hbox{mm}$ EJ-444 scintillation detector to be used for monitoring gross alpha and beta activity in tap water plants. Specific tests were performed in order to determine the best setup to read-out the light from the detector side. The possibility to stack many detectors and get a compact device with total active area of the order of $1~hbox{m}^2$ has been explored. Alpha/beta discrimination, efficiency and homogeneity tests were carried out with alpha and beta sources. Background from ambient radioactivity was measured as well. Alpha/beta real-time monitoring in drinking water is a goal of the EU project TAWARA_RTM.

Description: This paper describes an equipment for continuous measurement and identification of gamma radioactivity in aerosols developed by the Nuclear Engineering Research Group (NERG) at the Technical University of Catalonia (UPC) and Raditel Serveis i Subministraments Tecnològics, Ltd. A spectrometric analysis code has been specially designed for it. Spectrum analysis identifies and determines activity concentration of aerosol emitters captured by a fiberglass paper filter. This new equipment is currently operating in three radioactivity monitoring stations of the Environmental Radiological Surveillance Network of the Generalitat of Catalunya (local Catalan government): two near Ascó and Vandellòs Nuclear Power Plants in the province of Tarragona and one in the city of Barcelona. Two more monitors are expected to be deployed at Roses, Girona, Spain, and Puigcerdà, Barcelona, Spain. Measurements and evolution analysis results of emitters identified at these stations were also provided.

Description: In order to perform Quality Assurance/Quality Control (QA/QC) procedures for a system dedicated to the neutron interrogation of objects for the presence of threat materials one needs to perform measurements of reference materials (RM) i.e. simulants having the same (or similar) atomic ratios as real materials. It is well known that explosives, drugs, and various other benign materials, contain chemical elements such as hydrogen, oxygen, carbon and nitrogen in distinctly different quantities. For example, a high carbon-to-oxygen ratio (C/O) is characteristic of drugs. Explosives can be differentiated by measurement of both (C/O) and nitrogen-to-oxygen (N/O) ratios. The C/N ratio of the chemical warfare agents, coupled with the measurement of elements such as fluorine and phosphorus, clearly differentiate them from the conventional explosives. Here we present the RM preparation, calibration procedure and correlations attained between theoretical values and experimentally obtained results in laboratory conditions for C/O and N/C ratios of prepared hexogen (RDX), TNT, DLM2, TATP, cocaine, heroin, yperite, tetranitromethane, peroxide methylethylketone, nitromethane and ethyleneglycol dinitrate simulants. We have shown that analyses of the gamma ray spectra by using simple unfolding model developed for this purpose gave a nice agreement with the chemical formula of created simulants, thus the calibration quality was successfully tested.

Description: Time-of-flight (TOF) and coincident scattering measurements were conducted to measure the light response of a pressurized $^4{rm He}$ fast neutron scintillation detector as a function of deposited energy up to 5 MeV. The energy deposited in the detector by a neutron was measured by its angle of scatter and compared to the resulting light output. Whereas previous research has exclusively focussed on the energy information contained in the slow component, this work demonstrates that the fast component is also sensitive to neutron energy, and the entire scintillation signal can therefore be used. The gamma rejection capability of the detector was also measured for a variety of gamma sources. The detector demonstrated a inherent gamma rejection rate of 97.31%, which was increased to 99.89% after the application of pulse shape discrimination (PSD) algorithms. The characterization of gamma rejection and light response parameters will enable implementation of these detectors for neutron spectroscopy in mixed radiation fields.

Description: A neutron irradiation control method using a self-powered neutron detector (SPND) and zirconium foils was developed for neutron transmutation doping (NTD) application at HANARO. An SPND was installed at a fixed position of the upper part of the sleeve at the HANARO NTD hole for real-time monitoring of the neutron irradiation. The SPND signal output was significantly affected by the in-core conditions and surroundings of the facility. Furthermore, the SPND signal varied by $sim 15%$ throughout the reactor cycle according to the change of the control rod position. However, it was also confirmed that the variation of the neutron flux on the silicon ingots inside the irradiation rig was not significant for the control rod motion. In this procedure, the process for determining the thermal neutron flux by using zirconium foils was established for achieving efficient NTD irradiation. Accordingly, the relationship between the ratio of the neutron flux to the SPND output and the control rod position was deduced. Silicon irradiation experiments for transmutation doping were performed using the established relationship. The irradiated neutron fluence was controlled within ±1.3% of the target value. The mean irradiation/target ratio of the fluence was 0.9992, and the standard deviation was 0.0071. Thus, we confirmed that the produced irradiation was extremely accurate. This procedure can be useful in SPND applications requiring real-time high-accuracy neutron fluence measurements.

Description: We studied the responses of fiber-based temperature and strain sensors related to optical frequency domain reflectometry (OFDR) and exposed to high $gamma $ -ray doses up to 10 MGy. Three different commercial fiber classes are used to investigate the evolution of OFDR parameters with dose, thermal treatment and fiber core/cladding composition. We find that the fiber coating is affected by both thermal and radiation treatments and this modification results in an evolution of the internal stress distribution inside the fiber that influences its temperature and strain Rayleigh coefficients. These two environmental parameters introduce a relative error up to 5% on temperature and strain measures. This uncertainty can be reduced down to 0.5% if a prethermal treatment at 80 °C and/or a preirradiation up to 3 MGy are performed before insertion of the fiber in the harsh environment of interest. These preliminary results demonstrate that OFDR fiber-based distributed sensors look as promising devices to be integrated in radiation environments with associated large ionizing doses.

Description: Provides a listing of the editors, board members, and current staff for this issue of the publication.

Description: The aim of the research reported here is the development of a methodology for the measurement of small scale variations in chemical elements concentrations, in particular of carbon to oxygen ratio. Knowledge of the C/O ratio is of importance to many problems in various fields. Here we single out the application in obtaining important information about the oilfields. The most fundamental reservoir parameters–oil, gas and water content–are critical factors in determining how each oilfield should be developed. It is well established that carbon to oxygen ratio log yields accurate and repeatable data that can be used to identify and monitor reserves depletion. Recent improvements in neutron generator and gamma detector technologies resulted in small devices which allowed through-tubing measurements. Although the ratio of carbon and oxygen yields is a measure of the amount of oil around the tool it should be realized that a carbon signal can originate from several sources including the borehole, the cement behind the casing, the formation rock and the formation fluid. In order to evaluate these contributions individually we are proposing the modification of the neutron generator by insertion of segmented associated alpha particle detector. From the measurement of neutron time of flight spectra (alpha particle detector–start signal; gamma ray detector–stop signal) it would be possible to determine the location of gamma-ray production voxel and in such a way to determine radial variations in chemical elements concentrations, in particular of C/O ratio.

Description: Backscattering is a sensitive probe of the accuracy of electron scattering algorithms implemented in Monte Carlo codes. The capability of the Geant4 toolkit to describe realistically the fraction of electrons backscattered from a target volume is extensively and quantitatively evaluated in comparison with experimental data retrieved from the literature. The validation test covers the energy range between approximately 100 eV and 20 MeV, and concerns a wide set of target elements. Multiple and single electron scattering models implemented in Geant4, as well as preassembled selections of physics models distributed within Geant4, are analyzed with statistical methods. The evaluations concern Geant4 versions from 9.1 to 10.1. Significant evolutions are observed over the range of Geant4 versions, not always in the direction of better compatibility with experiment. Goodness-of-fit tests complemented by categorical analysis tests identify a configuration based on Geant4 Urban multiple scattering model in Geant4 version 9.1 and a configuration based on single Coulomb scattering in Geant4 10.0 as the physics options best reproducing experimental data above a few tens of keV. At lower energies only single scattering demonstrates some capability to reproduce data down to a few keV. Recommended preassembled physics configurations appear incapable of describing electron backscattering compatible with experiment. With the support of statistical methods, a correlation is established between the validation of Geant4-based simulation of backscattering and of energy deposition.

Description: Extraction of radiation dose information from MOSFET (RADFET) based dosimetry systems usually relies on biasing the MOSFET during readout at zero temperature coefficient drain current ( ${{mbi {I}}_{{ZTC}}}$ ), measured before irradiation. This current can vary due to accumulated radiation doses and thermal fluctuations, which degrades dosimetric accuracy. This work presents a method to reduce thermal drift related to this ${{mbi {I}}_{{ZTC}}}$ shift. It is based on biasing with two carefully chosen currents during readout according to a thermal model suitable for MOSFETs. An experiment including irradiation and thermal cycles has been carried out to test the proposed method, using five types of RADFETs with three different gate-oxide thicknesses. If we compare the thermal drift of the output voltage measured using our proposed method with that measured using the usual constant ${{mbi {I}}_{{ZTC}}}$ method, the linear thermal coefficient shows reductions of 33% to 80% for ${mbi{I}_{{ZTC}}}$ shifts between $-15%$ and $ + 65% $ .

Description: We experimentally characterized and compared the soft error rates of 65-nm bulk and silicon on thin buried oxide (SOTB) SRAMs by conducting accelerated alpha and neutron irradiation tests. Measurement results show that an SOTB SRAM has better soft error immunity than a bulk SRAM. In particular, the number of 2-bit multiple cell upsets (MCUs) of SOTB SRAM was smaller by two orders of magnitude than that of bulk SRAM, and the number of 3-bit or larger MCUs decreased further. In addition, the reverse body bias (RBB) reduced the soft error rate of SOTB SRAM to two-thirds of zero body bias (ZBB). To investigate this dependence on body bias, we evaluated the sensitive cross sectional area for ZBB and RBB with 3D technology computer aided design device simulations. The simulation results show that the RBB decreases the sensitive cross-sectional area of an SOTB device for small linear energy transfer (LET) ions, which is consistent with the measured dependence on body bias.

Description: This work deals with the on-line neutron flux mapping of the OPAL research reactor. A specific irradiation device has been set up to investigate fuel coolant channels using subminiature fission chambers to get thermal neutron flux profiles. Experimental results are compared to first neutronic calculations and show good agreement (C/E $sim 0.97$ ).

Description: The properties of the combined effect between ionization and displacement defects have been researched on the base-collector junctions of 3DG110 silicon NPN bipolar junction transistors (BJTs) irradiated by 6 MeV carbon (C) ions with different fluence. The Gummel curve is used to characterize the degradation of the current gain at a given fluence. Nonlinear relationship, induced by 6 MeV C ions with lower fluence, between irradiation fluence and BJT radiation response can be observed, which is attributed to the combined effect. Evolution of deep level centers is characterized by the deep level transient spectroscopy (DLTS) with various biases. An unusual discovery is that the deep level centers decrease in the amplitude of DLTS peaks with increasing the biases. Based on the results of DLTS measurement, interface traps caused by 6 MeV C ions produce apparent enhanced effect to displacement defects in the base-collector junction of NPN BJT. Meanwhile, two factors, including bias used in DLTS measurement and irradiation fluence, can influence characteristics of DLTS signals caused by oxide-trapped charge. With increasing the bias or the irradiation fluence, both the height and the temperature of the defect peaks induced by the oxide charge in DLTS spectra will increase, illustrating concentration and energy level of the defects are enhanced.

Description: Microdosimetry is an extremely useful technique, used for dosimetry in unknown mixed radiation fields typical of space and aviation, as well as in hadron therapy. A new silicon microdosimeter with 3D sensitive volumes has been proposed to overcome the shortcomings of the conventional Tissue Equivalent Proportional Counter. In this article, the charge collection characteristics of a new 3D mesa microdosimeter were investigated using the ANSTO heavy ion microprobe utilizing 5.5 MeV ${rm He}^{2 +}$ and 2 MeV ${rm H}^ {+}$ ions. Measurement of the microdosimetric characteristics allowed for the determination of the Relative Biological Effectiveness of the $^{12}{rm C}$ heavy ion therapy beam at the Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan. Well-defined sensitive volumes of the 3D mesa microdosimeter have been observed and the microdosimetric RBE obtained showed good agreement with the TEPC. The new 3D mesa “bridge” microdosimeter is a step forward towards a microdosimeter with fully free-standing 3D sensitive volumes.

Description: Most classical approaches of single event effect rate prediction are based on the rectangular parallelepiped model of sensitive volume. However it is not clear about the number of sensitive volume in the device when predicting the in-flight single event latchup rate. As for memory device, there are two empirical practices to deal with the latchup sensitive volume number: one assumes that there is only one sensitive volume in the whole device; another assumes that there are as much sensitive volumes as the number of memory cells. The latchup sensitive volume number of a 4M-bits SRAM is determined as 63360 using pulsed laser mapping test in this work first. Based on the two assumed and measured sensitive volume number, the single event latchup rates of the device are calculated and compared. The results show that pulsed laser could be a powerful tool to obtain the real sensitive volume number in the device, which is significant for single event latchup rate prediction. The latchup rate will be either overestimated or underestimated with the assumption of the sensitive volume number as one or as much as the number of memory cells.

Description: Indium doped cesium iodide (CsI:In) single crystals were grown by the Bridgman method. A comparison study of the scintillation properties of our CsI:In and commercially available CsI:Tl single crystals was carried out, including scintillation decay time, energy resolution, non-proportionality, absolute light yield, and afterglow. Under X-ray excitation, the CsI:In emission corresponds to a symmetrical broad band centered at 545 nm. Its scintillation decay time is $1.99 pm 0.02~muhbox{s}$ at room temperature under $^{137}{rm Cs}gamma $ -ray excitation. The CsI:In light yield was found to be $34,700 pm 1735$ photons per MeV with an energy resolution of $9.1 pm 0.3% $ , based on the pulse height spectra under $^{137}{rm Cs}$ excitation. The afterglow level of CsI:In over 130 ms after pulsed X-ray excitation was two orders of magnitude higher than that of CsI:Tl.

Description: Proton radiation damage and short-term annealing are investigated for lithium niobite ( ${rm LiNbO}_{2}$ ) mixed electronic-ionic memristors. Radiation damage and short-term annealing were characterized using Electrochemical Impedance Spectroscopy (EIS) to determine changes in the device resistance and the lithium ion mobility. The radiation damage resulted in a 0.48% change in the resistance at a fluence of ${10^{14}}~hbox{cm}^{ - 2}$ . In-situ short-term annealing at room temperature reduced the net detrimental effect of the damage with a time constant of about 9 minutes. The radiation damage mechanism is attributed predominantly to displacement damage at the niobium and oxygen sites trapping lithium ions that are responsible for induced polarization within the material. Short term annealing is attributed to room temperature thermal annealing of these defects, freeing the highly mobile lithium ions.

Description: These instructions give guidelines for preparing papers for this publication. Presents information for authors publishing in this journal.

Description: The Affiliate Plan, established by the IEEE Board of Directors, enables individuals who are not members of the IEEE, but who have an interest in the field of plasma science, to join the IEEE Nuclear and Plasma Sciences Society. Admission as an affiliate requires only membership in a professional society listed below. Affiliates pay a special fee and have all Society privileges except that of holding elective office. Affiliates receive the IEEE TRANSACTIONS ON NUCLEAR SCIENCE.

Description: The goal of the present work was to compare the image quality obtained on a new ToF PET/MR prototype with that of equivalent state-of-the-art standalone systems. The MR image quality of this system was tested by scanning a volunteer with a comprehensive brain protocol. The same exact acquisition was repeated before and after the PET detectors were installed. Furthermore, a baseline measurement was acquired by importing the protocol on a GE Discovery 750 w MR system and repeating the acquisition on the same subject. The obtained datasets were registered and reviewed by medical doctors with experience in both radiology and nuclear imaging. Structure detectability, delineation and noise ratio were considered. MR image quality was shown to be virtually identical between the hybrid (pre- and post-insert) and standalone systems. We conclude that clinical MR sequences are not qualitatively affected by the presence of the PET detector insert.

Description: Provides a listing of current staff, committee members and society officers.

Description: In 2012, we presented the Hyperion-II $^{rm D}$ preclinical PET insert which uses Philips Digital Photon Counting’s digital SiPMs and is designed to be operated in a 3-T MRI. In this work we use the same platform equipped with scintillators having dimensions closer to a clinical application. This allows an investigation of the time of flight (ToF) performance of the platform and its behavior during simultaneous MR operation. We employ LYSO crystal arrays of $4times 4 times 10~hbox{mm}^{3}$ coupled to $4 times 4$ PDPC DPC 3200-22 sensors (DPC) resulting in a one-to-one coupling of crystals to read-out channels. Six sensor stacks are mounted onto a singles processing unit in a $2 times 3$ arrangement. Two modules are mounted horizontally facing each other on a gantry with a crystal-to-crystal spacing of 217.6 mm (gantry position). A second arrangement places the modules at the maximum distance of approximately 410 mm inside the MR bore (maximum distance position) which brings each module close to the gradient system. The DPCs are cooled down to approximately $5 - {10^ circ }{rm C}$ under operation. We disable 20% of the worst cells and use an overvoltage of ${V_{{rm ov}}} = 2.0~hbox{V}$ and 2.5 V. To obtain the best time stamps, we use the trigger scheme 1 (first photon trigger), a narrow energy window of $511 pm 50~hbox{keV}$ and a minimum required light fraction of the main pixel of more than 65% to reject intercrystal scatter. By using a $^{22}hbox{Na}$ point source in the isocenter of the modules, the coincidence resolution time (CRT) of the two modules is evaluated inside the MRI system without MR activity and while using highly demanding gradient sequences. Inside the ${{rm B}_0}$ field without any MR activity at an overvoltage of ${V_{{rm ov}}} = 2.0~hbox{V}$ , the energy resolution is 11.45% (FWHM) and the CRT is 250 ps (FWHM). At an overvoltage of ${V_{{rm ov}}} = 2.5~hbox{V}$ , the energy resolution is 11.15% (FWHM) and the CRT is 240 ps (FWHM). During a heavy $z$ -gradient sequence (EPI factor: 49, gradient strength: 30 mT/m, slew rate: 192.3 mT/m/ms, TE/TR: 12/25 ms and switching duty cycle: 67%) at the gantry position and an overvoltage of ${V_{{rm ov}}} = 2.0~hbox{V}$ , the energy resolution is degraded relatively by 4.1% and the CRT by 25%. Using the same sequence but at the maximum distance position and an overvoltage of ${V_{{rm ov}}} = 2.5~hbox{V}$ , we measure a degradation of the energy resolution of 9.2% and a 52% degradation of the CRT. The Hyperion-II $^{rm D}$ platform proofs to deliver good timing performance and energy resolution inside the MRI system even under highly demanding gradient sequences.

Description: In positron emission tomography (PET) systems, light sharing techniques are commonly used to readout scintillator arrays consisting of scintillation elements, which are smaller than the optical sensors. The scintillating element is then identified evaluating the signal heights in the readout channels using statistical algorithms, the center of gravity (COG) algorithm being the simplest and mostly used one. We propose a COG algorithm with a fixed number of input channels in order to guarantee a stable calculation of the position. The algorithm is implemented and tested with the raw detector data obtained with the Hyperion-II $^{rm D}$ preclinical PET insert which uses Philips Digital Photon Counting’s (PDPC) digitial SiPMs. The gamma detectors use LYSO scintillator arrays with $30 times 30$ crystals of $1 times 1 times 12~hbox{mm}^3$ in size coupled to $4 times 4$ PDPC DPC 3200-22 sensors (DPC) via a 2-mm-thick light guide. These self-triggering sensors are made up of $2 times 2$ pixels resulting in a total of 64 readout channels. We restrict the COG calculation to a main pixel, which captures most of the scintillation light from a crystal, and its (direct and diagonal) neighboring pixels and reject single events in which this data is not fully available. This results in stable COG positions for a crystal element and enables high spatial image resolution. Due to the sensor layout, for some crystals it is very likely that a single diagonal neighbor pixel is missing as a result of the low light level on the corresponding DPC. This leads to a loss of sensitivity, if these events are rejected. An enhancement of the COG algorithm is- proposed which handles the potentially missing pixel separately both for the crystal identification and the energy calculation. Using this advancement, we show that the sensitivity of the Hyperion-II $^{rm D}$ insert using the described scintillator configuration can be improved by 20–100% for practical useful readout thresholds of a single DPC pixel ranging from 17–52 photons. Furthermore, we show that the energy resolution of the scanner is superior for all readout thresholds if singles with a single missing pixel are accepted and correctly handled compared to the COG method only accepting singles with all neighbors present by 0–1.6% (relative difference). The presented methods can not only be applied to gamma detectors employing DPC sensors, but can be generalized to other similarly structured and self-triggering detectors, using light sharing techniques, as well.

Description: The Multimodal Imaging Brain Connectivity Analysis (MIBCA) toolbox is a fully automated all-in-one connectivity analysis toolbox that offers both pre-processing, connectivity, and graph theory analysis of multimodal images such as anatomical, diffusion, and functional MRI, and PET. In this work, the MIBCA functionalities were used to study Alzheimer’s Disease (AD) in a multimodal MR/PET approach. Materials and Methods: Data from 12 healthy controls, and 36 patients with EMCI, LMCI and AD (12 patients for each group) were obtained from the Alzheimer’s Disease Neuroimaging Initiative (ADNI) database (adni.loni.usc.edu), including T1-weighted (T1-w), Diffusion Tensor Imaging (DTI) data, and 18F-AV-45 (florbetapir) dynamic PET data from 40-60 min post injection (4x5 min). Both MR and PET data were automatically pre-processed for all subjects using MIBCA. T1-w data was parcellated into cortical and subcortical regions-of-interest (ROIs), and the corresponding thicknesses and volumes were calculated. DTI data was used to compute structural connectivity matrices based on fibers connecting pairs of ROIs. Lastly, dynamic PET images were summed, and the relative Standard Uptake Values calculated for each ROI. Results: An overall higher uptake of 18F-AV-45, consistent with an increased deposition of beta-amyloid, was observed for the AD group. Additionally, patients showed significant cortical atrophy (thickness and volume) especially in the entorhinal cortex and temporal areas, and a significant increase in Mean Diffusivity (MD) in the hippocampus, amygdala and temporal areas. Furthermore, patients showed a reduction of fiber connectivity with the progression of the disease, especially for intra-hemispherical connections. Conclusion: This work shows the potential of the MIBCA toolbox for the study of AD, as findings were shown to be in agreement with the literature. Here, only structural changes and beta-amyloid accumulation were considered. Y- t, MIBCA is further able to process fMRI and different radiotracers, thus leading to integration of functional information, and supporting the research for new multimodal biomarkers for AD and other neurodegenerative diseases.

Description: In the recent decade, pixelated CsI(Tl) scintillation films are developed for X-ray imaging to improve spatial resolution. Several methods have been reported but better performance is still required. In this work, CsI(Tl) films were prepared on specially designed patterned substrates with regular arrays of pits. Each CsI(Tl) micro-column locates in one pit. In this way, CsI(Tl) films with pixel-like columnar-matrix structure were achieved. Each pixel contains one micro-column and the size of pixel is the average diameter of the columns. Morphologies of the films were examined by scanning electron microscopy. Imaging performances of films dependent on their structure are discussed. The prepared CsI(Tl) films show superior image performance and may be well-coupled with pixelated photo sensors for X-ray imaging systems.

Description: Metabolic imaging techniques can potentially improve detection and diagnosis of cancer in women with radiodense and/or fibrocystic breasts. Our group has previously developed a high-resolution positron emission tomography imaging and biopsy device (PEM-PET) to detect and guide the biopsy of suspicious breast lesions. Initial testing revealed that the imaging field-of-view (FOV) of the scanner was smaller than the physical size of the detector’s active area, which could hinder sampling of breast areas close to the chest wall. The purpose of this work was to utilize segmented, tapered light guides for optically coupling the scintillator arrays to arrays of position-sensitive photomultipliers to increase both the active FOV and identification of individual scintillator elements. Testing of the new system revealed that the optics of these structures made it possible to discern detector elements from the complete active area of the detector face. In the previous system the top and bottom rows and left and right columns were not identifiable. Additionally, use of the new light guides increased the contrast of individual detector elements by up to 129%. Improved element identification led to a spatial resolution increase by approximately 12%. Due to attenuation of light in the light guides the detector energy resolution decreased from 18.5% to 19.1%. Overall, these improvements should increase the field-of-view and spatial resolution of the dedicated breast-PET system.

Description: This paper evaluates the performance of a new type of PET detectors called sensitivity encoded silicon photomultiplier (SeSP), which allows a direct coupling of small-pitch crystal arrays to the detector with a reduction in the number of readout channels. Four SeSP devices with two separate encoding schemes of 1D and 2D were investigated in this study. Furthermore, both encoding schemes were manufactured in two different sizes of $ 4 times 4~hbox{mm}^ 2$ and $ 7. 73 times 7. 9~hbox{mm}^ 2$ , in order to investigate the effect of size on detector parameters. All devices were coupled to LYSO crystal arrays with 1 mm pitch size and 10 mm height, with optical isolation between crystals. The characterization was done for the key parameters of crystal-identification, energy resolution, and time resolution as a function of triggering threshold and over-voltage (OV). Position information was archived using the center of gravity (CoG) algorithm and a least squares approach (LSQA) in combination with a mean light matrix around the photo-peak. The positioning results proved the capability of all four SeSP devices in precisely identifying all crystals coupled to the sensors. Energy resolution was measured at different bias voltages, varying from 12% to 18% (FWHM) and paired coincidence time resolution (pCTR) of 384 ps to 1.1 ns was obtained for different SeSP devices at about 18 $^{circ} $ C room temperature. However, the best time resolution was achieved at the highest over-voltage, resulting in a noise ratio of 99.08%.

Description: Sphinx1 is a novel pixel architecture adapted for X-ray imaging that can detect radiation by photon counting and by charge integration. In photon counting mode, each photon is compensated by one or more counter-charge packets which can be dimensioned at a level as low as 100 electrons and the number of injected counter-charge packets indicates the incoming photon energy, thus allowing a spectrometric detection. The pixel is also able to detect radiation by integrating the charges deposited by all incoming photons and converting this analog value into a digital data with a least significant bit (LSB) of 100 electrons through the use of the counter-charge concept. In this paper, Sphinx1 pixel architecture is presented with emphasis on the counter-charge design, and the two modes of operation are described in detail. The pixel was simulated using Eldo simulator. Simulation results indicate an equivalent noise charge (ENC) of 48 electrons-rms for a detector capacitance of 75 fF. The LSB linearity and the ENC are further studied for different values of detector capacitances. The analog and digital power consumptions are calculated to be less than $1~muhbox{W}$ in static conditions, proving the architecture to be suitable for large area detectors. Finally, corner simulations show a consistent performance against transistors mismatch. Proof of concept test chip of $ 5~hbox{mm}times5~hbox{mm}$ . test chip is being designed fabricated in CMOS $0.13~muhbox{m}$ technology, with a pixel pitch of $200 ~muhbox{m}$ .

Description: Single Photon Avalanche Diodes (SPAD) are known for their excellent timing performance which enables Time of Flight capabilities in positron emission tomography (PET). However, current array architectures juxtapose the SPAD with its ancillary electronics at the expense of a poor fill factor of the SPAD array. The 3D vertical integration of SPADs and readout electronics represents a solution to the aforementioned problem. Compared to systems with external electronics readout, 3D vertical integration reduces the SPAD interconnect parasitic capacitance while greatly increasing the photosensitive area and improving overall performances. This paper presents the implementation of two SPAD structures designed for PET. The SPAD structures are designed using Teledyne DALSA high voltage (HV) CMOS technology targeted for a 3-dimensional single photon counting module (3DSPCM). SPAD with two types of guard ring (diffusion-based and virtual guard ring) are designed, fabricated and characterized. All structures are based on a $p + $ anode in an $n$ -well cathode and are implemented along with active quenching circuits for proper characterization. The results show that the contact distribution and the anode-cathode spacing impact the dark count rate (DCR). The design of SPADs with a diffusion guard ring have a DCR down to $3~hbox{s}^{- 1}mu hbox{m}^{-2}$ at room temperature, afterpulsing probability of $ 〈 2% $ , timing resolution of 27 ps FWHM and PDE of 49% at 480 nm.

Description: In this paper, we present the characterization of a novel $4~hbox{mm} times 4~hbox{mm}$ position-sensitive silicon photomultiplier, called linearly-graded SiPM (LG-SiPM). The 2D position encoding is obtained through a charge sharing approach, implemented by means of a current divider directly integrated on die. The microcells of the detectors have a size of $45~muhbox{m} times 45~mu hbox{m}$ and are fabricated with the FBK RGB (Red Green Blue) technology, modified with the addition of a second metal interconnection layer and a second quenching resistor in every cell, required by the encoding architecture. We verified that the LG-SiPM scheme does not alter the signal temporal shape, when illuminating the detector in different positions. We performed a XY scan with light spots of 1 mm diameter and spaced by 0.25 mm, showing that the reconstructed positions are easily separated. No visible pincushion distortion was present. We measured the energy resolution and the encoding capability in PET-like and in SPECT-like conditions using pixelated LYSO and CsI(Tl) crystal arrays (with 0.8 and 1 mm pitch, respectively), irradiating them with 511 keV and 122 keV photons, respectively. In both cases, we were able to clearly distinguish the scintillator pixels.

Description: Scintillation properties of LSO:Ce, LSO:Ce,0.2%Ca, LYSO:Ce, LYSO:0.11%Ce,0.2%Mg, and LYSO:0.2%Ce,0.2%Ca were studied for application in time-of-flight positron emission tomography. To find the scintillation material with the best timing performance among those, we measured intrinsic scintillation pulse shapes–defined as the number of photons emitted per unit time at the ionization track as a function of time - by means of 100 ps x-ray excitation in the temperature range from 193 K to 373 K, from which intrinsic rise and decay time constants were derived. Photoelectron yields were measured by 662 keV gamma excitation. From these scintillation properties we calculated the corresponding lower bound on the timing resolution for each material.

Description: Devices aiming at combined Positron Emission Tomography (PET) and Magnetic Resonance Imaging (MRI) to enable simultaneous PET/MR image acquisition have to fulfill demanding requirements to avoid mutual magnetic- as well as electromagnetic-field-related interferences which lead to image quality degradation. Particularly Radio-Frequency (RF)-field-related interferences between PET and MRI may lead to MRI SNR reduction, thereby deteriorating MR image quality. RF shielding of PET electronics is therefore commonly applied to reduce RF emission and lower the potential coupling into MRI RF coil(s). However, shields introduce eddy-current-induced MRI field distortions and should thus be minimized or ideally omitted. Although the MRI noise floor increase caused by a PET system might be acceptable for many MRI applications, some MRI protocols, such as fast or high-resolution MRI scans, typically suffer from low SNR and might need more attention regarding RF silence to preserve the intrinsic MRI SNR. For such cases, we propose RESCUE, an MRI-synchronously-gated PET data acquisition technique: By interrupting the PET acquisition during MR signal receive phases, PET-related RF emission may be minimized, leading to MRI SNR preservation. Our PET insert $Hyperion II^D$ using Philips Digital Photon Counting (DPC) sensors serves as the platform to demonstrate RESCUE. To make the DPC sensor suitable for RESCUE to be applied for many MRI sequences with acquisition time windows in the range of a few milliseconds, we present in this paper a new technique which enables rapid DPC sensor operation interruption by dramatically lowering the overhead time to interrupt and restart the sensor operation. Procedures to enter and leave gated PET data acquisition may imply sensitivity losses which add to the ones occurring during MRI RF acquisition. For the case of our PET insert, the new DPC quick-interruption technique yields a PE- sensitivity loss reduction by a factor of 78 when compared to the loss introduced with the standard start/stop procedure. For instance, PET sensitivity losses related to overhead time are 2.9% in addition to the loss related to PET gating being equal to the MRI RF acquisition duty cycle (14.7%) for an exemplary T1-weighted 3D-FFE MRI sequence. MRI SNR measurement results obtained with one $Hyperion II^D$ Singles Detection Module (SDM) using no RF shield demonstrate a noise floor reduction by a factor of 2.1, getting close to the noise floor level of the SNR reference scan (SDM off-powered) when RESCUE was active.

Description: The design of an MRI (Magnetic Resonance Imaging) compatible PET (Positron Emission Tomography) detector is regarded to be a challenging task since both imaging devices are likely interacting with each other potentially leading to performance degradation. A typically expected consequence of this interaction is the distortion of the MRI system’s ${B_0}$ field homogeneity. The ${B_0}$ field gets distorted by any material with non-zero susceptibility brought into the MRI system. Typically, MRI machines have a so-called active shimming system available which allows the field optimization by using additional dedicated shim coils. However, this active shimming mechanism is limited and might not be capable to compensate localized higher order field patterns caused by e.g. a PET system. Since the high ${B_0}$ field quality is needed for an undisturbed MRI acquisition in general and especially for more advanced MR sequences (spectroscopic studies, sequences which utilizes spectral selective pre-pulses), the PET system’s hardware needs to be designed carefully. Consequently, the typical design paradigm regarding this ${B_0}$ field distortion is the careful selection of all components according to their susceptibility (as low as possible). This design paradigm certainly limits the flexibility of the system design since worse performing components might be chosen over better alternatives because of their higher susceptibility. To overcome this limitation and to retain the MRI capabilities, we propose the application of localized shimming on PET detector level, meaning that the distortion profile caused by PET modules is compensated using either additional components such as magnetic materials (passi- e shimming) or DC coils (active shimming) on the PET modules or by intelligently arranging the hardware components of the PET detector. We have implemented a software framework which covers three parts: firstly, it calculates the ${B_0}$ distortion of various objects (susceptibility objects, conductor configuration). Secondly, it allows the characterization of magnetic objects by fitting the implemented models to data and thirdly, it performs a ${B_0}$ field homogenization of measured distortion maps by superimposing field disturbances of additional simulated objects. We tested this software framework in a first attempt with a single PET module of the Hyperion-II $^ {rm D}$ scanner. The measured distortion map of the single PET module shows a strong localized ${B_0}$ distortion with a volume RMS value of about $0.6~hbox{ppm}$ . After optimization, the homogeneity of the simulated field distribution is strongly improved by a factor of 8 (volume RMS $ approx 0.075~hbox{ppm}$ ).

Description: We have developed four-layered depth-of-interaction (DOI) detectors based on light sharing. Reflectors, which are inserted in every two lines of crystal segments and shifted differently depending on each layer, project 3-D crystal positions to a 2-D position histogram without any overlapping after applying the Anger-type calculation. The DOI measurement itself has the potential to improve time resolution because the depth-dependent timing delay can be corrected. However, light sharing tends to increase variance of light paths inside the crystal block, thus resulting in worsened time resolution. Although we have reported advantages of our DOI detectors in terms of position and energy resolutions, we had not evaluated their potential for time resolution. In this paper, therefore, we measured timing performance with the help of a digital photon counter (DPC), which offers precise control of event triggering. There are several studies that have reported one-to-one coupling of the scintillator to the DPC pixel, but DPCs have not been studied well for light-sharing detectors. Therefore, in this work, we optimized measurement parameters of the DPCs for our four-layered DOI detector. The DOI detector consists of 256 LGSO crystals which are arranged in four layers of ${8} times {8}$ arrays, coupled to the DPC array. Each crystal element is $2.9times 2.9 times 5~hbox{mm}^{3}$ . Each die of the DPC array provides an individual timestamp. Crystal identification performance largely depended on the dark count rate of the DPC array, which can be reduced by means of cell inhibition. We measured several conditions of the inhibition rate of microcells and temperature. For increased inhibition rate, we observed degraded time resolution, although positioning performance and energy resolution were improved. Regarding the temperature dependency within 1- to $ - 7 ^circ hbox {C}$ , we found that time resolution was insensitive. At 10 $ ^circ hbox {C}$ and 20% inhibition rate, average time resolution over all crystals was $267 pm 32~hbox{ps}$ (full width half maximum). Better positioning performance and energy resolution were obtained for colder temperatures.

Description: Computed tomography (CT) is currently the standard modality to provide anatomical reference for positron emission tomography (PET) in molecular imaging applications. Since both PET and CT rely on detecting radiation to generate images, using the same detection system for data acquisition is a compelling idea even though merging PET and CT hardware imposes stringent requirements on detectors. These requirements include large signal dynamic range with high signal-to-noise ratio for good energy resolution in PET and energy-resolved photon-counting CT, high pixelization for suitable spatial resolution in CT, and high count rate capability for reasonable CT acquisition time. To meet these criteria, the avalanche photodiode (APD)-based LabPET II module is proposed as the building block for a truly combined PET/CT scanner. The module is made of two monolithic $ 4times 8$ APD pixel arrays mounted side-by-side on a custom ceramic holder. Individual APD pixels have an active area of $ 1.1times 1.1~hbox{mm}^{2}$ at a 1.2 mm pitch. The APD arrays are coupled to a 12-mm high, $8 times 8$ LYSO scintillator array made of $1.12 times 1.12~hbox{mm}^{2}$ pixels also at a pitch of 1.2 mm to ensure direct one-to-one coupling to individual APD pixels. The scintillator array was designed with unbound specular reflective material between pixels to maximize the difference between refractive indices and enhance total internal reflection at the crystal side surfaces for better light collection, and the APD quantum efficiency was improved to $ sim60%$ at 420 nm to optimize intrinsic detector performance. Mean energy resolution was $20 pm 1%$ at 511 keV and $ 41pm 4%$ at 60 keV. The measured intrinsic spatial and time resolution for PET were respectively $0.81 pm 0.04~hbox{mm}~{rm FWHM}/1.57 pm 0.04~hbox{mm}$ FWTM and $ 3.6pm 0.3~hbox{ns}$ FWHM with an energy threshold of 400 keV. Initial phantom images obtained using a CT test bench demonstrated excellent contrast linearity as a function of material density. With a magnification factor of 2, a CT spatial resolution of 0.66 mm FWHM/1.2 mm FWTM, corresponding to 1.18 lp/mm at ${rm MTF}_{10%}/0.67~hbox{lp/mm}$ at ${rm MTF}_{50%}$ , was measured, allowing 0.75 mm air holes in an Ultra-Micro Hot Spot resolution phantom to be clearly distinguished.

Description: Recent investigations of Field Programmable Gate Array (FPGA)-based time-to-digital converters (TDCs) have predominantly focused on improving the time resolution of the device. However, the monolithic integration of multi-channel TDCs and the achievement of high measurement throughput remain challenging issues for certain applications. In this paper, the potential of the resources provided by the Kintex-7 Xilinx FPGA is fully explored, and a new design is proposed for the implementation of a high performance multi-channel TDC system on this FPGA. Using the tapped-delay-line wave union TDC architecture, in which a negative pulse is triggered by the hit signal propagating along the carry chain, two time measurements are performed in a single carry chain within one clock cycle. The differential non-linearity and time resolution can be significantly improved by realigning the bins. The on-line calibration and on-line updating of the calibration table reduce the influence of variations of environmental conditions. The logic resources of the 6-input look-up tables in the FPGA are employed for hit signal edge detection and bubble-proof encoding, thereby allowing the TDC system to operate at the maximum allowable clock rate of the FPGA and to achieve the maximum possible measurement throughput. This resource-efficient design, in combination with a modular implementation, makes the integration of multiple channels in one FPGA practicable. Using our design, a 128-channel TDC with a dead time of 1.47 ns, a dynamic range of 360 ns, and a root-mean-square resolution of less than 10 ps was implemented in a single Kintex-7 device.

Description: We have carried out a PET performance evaluation a silicon photo-multiplier (SiPM) based PET scanner designed for fully simultaneous pre-clinical PET/MR studies. The PET scanner has an inner diameter of 20 cm with an LYSO crystal size of 1.3 by 1.3 by 10 mm. The axial PET field of view (FOV) is 30.2 mm. The PET detector modules, which incorporate SiPMs, have been designed to be MR-compatible allowing them to be located directly within a Philips Achieva 3T MR scanner. The spatial resolution of the system measured using a point source in a non-active background, is just under 2.3 mm full width at half maximum (FWHM) in the transaxial direction when single slice rebinning (SSRB) and 2D filtered back-projection (FBP) is used for reconstruction, and 1.3 mm FWHM when resolution modeling is employed. The system sensitivity is 0.6% for a point source at the center of the FOV. The true coincidence count rate shows no sign of saturating at 30 MBq, at which point the randoms fraction is 8.2%, and the scatter fraction for a rat sized object is approximately 23%. Artifact-free images of phantoms have been obtained using FBP and iterative reconstructions. The performance is currently limited because only one of three axial ring positions is populated with detectors, and due to limitations of the first-generation detector readout ASIC used in the system. The performance of the system as described is sufficient for simultaneous PET-MR imaging of rat-sized animals and large organs within the mouse. This is demonstrated with dynamic PET and MR data acquired simultaneously from a mouse injected with a dual-labeled PET/MR probe.

Description: A Small Animal PET detector block made with a Dual Layer Offset crystal array with 1.27 mm wide LYSO crystals on a Philips PDC3200-22-44 Digital Photon Counter (DPC) array was characterized while operating near room temperature. Crystal map peak to valley ratio, energy resolution, and timing resolution were characterized as a function of various device settings of the DPC and temperature. In addition, rates of count loss due to the phenomena of incomplete neighbor logic and dark-readout deadtime were measured. Device settings of interest were: Trigger scheme–defining the threshold of when a DPC will generate a timestamp and enter a readout cycle, inhibit fraction–the fraction of noisy cells which are disabled, and RTL-refresh–a setting which reduces the probability of the DPC being triggered from dark noise. At 15 $^circ {rm C}$ , peak to valley ratios were measured to be around 11, and energy resolution around 11.5% regardless of device settings. Timing resolution ranged from near 300 ps to 1.5 ns. Count loss from dark readout deadtime was insignificant compared to incomplete neighbor logic, which ranged from as high as 95% to 5% of coincidences. It was found that trade-offs had to be made between timing resolution and count loss. With the most optimal device settings for small animal PET, a timing resolution of 1.4 ns and coincidence losses of 5% were achieved. At these settings, the detector block had little sensitivity to a 5 $^circ {rm C}$ temperature fluctuation.

Description: For continuous crystal-based PET detectors, not only the two-dimensional (2D) plane coordinate of the interaction point, but also the depth-of-interaction (DOI) of the ${gammab}$ event could be precisely estimated by the single-end readout of the scintillation light. In this paper, we propose a practical method for DOI determination for continuous crystal PET detectors. By self-organizing map (SOM) neural network with unsupervised learning, the perpendicularly irradiated reference events in each reference position are classified into a certain number of groups, which are simultaneously used for the plane coordinate estimation and the DOI decoding. The reference events measured in an oblique irradiation are used to generate the initial weights of the SOM neurons and to calibrate the DOI decoding. Applying the new method to our experimental data, the SOM-based DOI estimation could achieve an average resolution of 2.56 mm over the whole thickness (0 - 10 mm) of the crystal. The DOI effect is also evaluated by comparing the plane position resolutions of the test beams in different incident angles with and without the DOI correction. The test results show that the DOI determination could seamlessly integrate into our previously proposed the SOM-based plane coordinate estimation scheme to realize the high performance real-time three-dimensional position estimation for continuous crystal-based PET detectors.

Description: A new phoswich detector is being developed at the Crump Institute, aiming to provide improvements in sensitivity, and spatial resolution for PET. The detector configuration is comprised of two layers of pixelated scintillator crystal arrays, a glass lightguide and a light detector. The annihilation photon entrance (top) layer is a $48times48$ array of $1.01 times 1.01 times7 ~hbox{mm}^{3}$ LYSO crystals. The bottom layer is a $32 times 32$ array of $1.55 times1.55 times 9~hbox{mm}^{3}$ BGO crystals. A tapered, multiple-element glass lightguide is used to couple the exit end of the BGO crystal array ( $52 times 52~hbox{mm}^{2}$ ) to the photosensitive area of the Position Sensitive Photomultiplier Tube ( $46 times 46~hbox{mm}^{2}$ ), allowing the creation of flat panel detectors without gaps between the detector modules. Both simulations and measurements were performed to evaluate the characteristics and benefits of the proposed design. The GATE Monte Carlo simulation indicated that the total fraction of the cross layer crystal scatter (CLCS) events in singles detection mode for this detector geometry is 13.2%. The large majority of these CLCS events (10.1% out of 13.2%) deposit most of their energy in a scintillator layer other than the layer of first interaction. Identification of those CLCS events for rejection or correction may lead to improvements in data quality and imaging performance. Physical measurements with the prototype detector showed that the LYSO, BGO and CLCS events were successfully identified using the delayed charge integration (DCI) technique, with- more than 95% of the LYSO and BGO crystal elements clearly resolved. The measured peak-to-valley ratios (PVR) in the flood histograms were 3.5 for LYSO and 2.0 for BGO. For LYSO, the energy resolution ranged from 9.7% to 37.0% full width at half maximum (FWHM), with a mean of $13.4 pm 4.8%$ . For BGO the energy resolution ranged from 16.0% to 33.9% FWHM, with a mean of $18.6pm 3.2%$ . In conclusion, these results demonstrate that the proposed detector is feasible and can potentially lead to a high spatial resolution, high sensitivity and DOI PET system.

Description: In small-animal Positron Emission Tomography (PET), spatial resolution improvements rely on detector minimization in size and often come at the expense of lowering the detector photoelectric fraction. As a result, Inter-Crystal Scatter (ICS) occurrences are increased and affect the overall PET detection efficiency. To reclaim some lost efficiency, previous work used an artificial neural network (ANN) to identify the true line of response (LOR) for the simplest multiple event detection case, three coincident singles known as triplets. Despite promising results, this method is limited to an offline processing which is impractical when a limited data bandwidth is present between the scanner and the PC. This paper demonstrates the capability of processing triplets in real time using an ANN implemented in the field-programmable gate array (FPGA). The ANN pipelined architecture can process over 1 million triplets/second using less than 6000 FPGA slices. Real time processing on the LabPET I scanner yielded an overall 39.7% increase in detection efficiency relative to traditional high resolution settings with a 360-660 keV energy window along with a slight Contrast-to-Noise Ratio ( $CNR$ ) degradation. Although improvements are still possible, the proposed FPGA implementation proves the usability of an ANN in real time PET applications in conditions where spare computational resources are limited and the data rate to be processed is high.

Description: Compact SPECT systems with cadmium zinc telluride (CZT) solid-state detectors with improved energy resolution and shorter acquisition times have recently been introduced. These systems have, however, different energy characteristics compared to NaI(Tl) crystal-based cameras; therefore, a need exists to develop new simulation models for these cameras. We modeled the charge transport within the CZT detectors for a GE Discovery 530c/570c SPECT system with multiple pinhole collimators employing the SIMIND Monte Carlo program and validated simulations against measurements. The incomplete charge collection between the anode and cathode in the pixilated CZT was modeled with the Hecht equation. The simulation also included charge-sharing effects across pixels due to physical interactions and charge diffusion. To validate our CZT-model, $^{99{rm m}}{rm Tc}$ and $^{123}{rm I}$ point sources and a $^{201}{rm Tl}$ line source were acquired and measured. Measured energy spectra were compared with simulated energy spectra. The Monte Carlo simulated energy spectra agreed well with the experimental measurements within the photopeak, overestimated the k-edge x-ray escape peaks of cadmium and telluride, and slightly underestimated the remainder of the tail. Comparisons of system sensitivity and spatial resolution were also conducted for an array of point source locations with results showing excellent agreement. Lastly, to demonstrate a clinically realistic case, a simulation of an anthropomorphic phantom with a cardiac insert and an inferior defect was performed. Simulated projections were processed using the GE Xeleris software confirming the accuracy of the SIMIND geometry. We conclude that it is feasible to simulate the GE Discovery 530c/570c SPECT system using the SIMIND code.

Description: Segmentation of dynamic PET images is needed to extract the time activity curves (TAC) of regions of interest (ROI). These TAC can be used in compartmental models for in vivo quantification of the radiotracer target. While unsupervised clustering methods have been proposed to segment PET sequences, they are often sensitive to initial conditions or favour convex shaped clusters. Kinetic spectral clustering (KSC) of dynamic PET images was recently proposed to handle arbitrary shaped clusters in the space in which they are identified. While improved results were obtained with KSC compared to three state of art methods, its use for clinical applications is still hindered by the manual setting of several parameters. In this paper, we develop an extension of KSC to automatically estimate the parameters involved in the method and to make it deterministic. First, a global search procedure is used to locate the optimal cluster centroids from the projected data. Then an unsupervised clustering criterion is tailored and used in a global optimization scheme to automatically estimate the scale parameter and the weighting factors involved in the proposed Automatic and Deterministic Kinetic Spectral Clustering (AD-KSC). We validate the method using GATE Monte Carlo simulations of dynamic numerical phantoms and present results on real dynamic images. The deterministic results obtained with AD-KSC agree well with those obtained with optimal manual parameterization of KSC, and improve the ROI identification compared to three other clustering methods. The proposed approach could have significant impact for quantification of dynamic PET images in molecular imaging studies.

Description: This paper investigates some potential methods for few-view tomography, and investigates the cause and remedy of the staircase artifacts. This paper also discusses whether there is any benefit to use edge-preserving filters in emission tomography. We formulate a general Green’s one-step-late algorithm, so that it can incorporate any linear or non-linear filters. We argue that the derivative of the penalty function can be “artificially” created, not naturally derived from a penalty function. We have gained more insight into constrained image reconstruction especially with edge-preserving constraints. Our numerical results show that the bilateral method can have better performance than the TV method, and higher order methods may not be necessary for non-piecewise-constant objects.

Description: Positron emission tomography (PET) images usually suffer from low spatial resolution mainly because of the finite dimension of crystals. To improve the spatial resolution based on wobble scanning, we previously proposed a sinogram-based super-resolution (SR) algorithm using a space-variant blur matrix. However, the algorithm may cause unwanted resolution loss owing to an inevitable interpolation process for preparing evenly spaced projections. In this article, we propose a novel one-step line of response (LOR)-based SR framework for 3D PET images. In the framework, we efficiently determine a large number of space-variant point spread functions (PSFs) in the image space by using the scanner symmetries and the proposed PSF interpolation scheme based on nonrigid registration. Furthermore, to minimize the resolution degradation in the evenly spaced parallel-beam rebinning and to reduce the computational time in the graphics processing unit (GPU) implementation, we introduce parallel-friendly LOR reconstruction based on cone-beam reordering. We then obtain a high resolution image via a one-step super-resolved 3D PET image reconstruction with the determined PSFs. The proposed framework provides noticeable improvement on the spatial resolution of PET images with a considerable reduction of computational time.

Description: In this paper, the noise of 3D computed tomography (CT) image reconstruction using QR-Decomposition is analyzed. There are several types of image noise that can interfere with the interpretation of an image. Here, the noise introduced by the reconstruction process is studied. In this analysis, condition numbers are calculated with different CT model parameters, three dimensional (3D) CT image reconstruction with simulated and real data are performed, image noise analysis is performed through various image quality parameters and the condition number of the linear system is related with the image quality parameters. Results show the condition number’s dependence on the CT model. Image reconstructions with simulated data show errors significantly below the condition number theoretical bound and image reconstructions with real data show that quality improvements depend strongly on the condition number. This allows a reduction on the number of projections without compromising image quality and places this reconstruction method as a strong candidate for low-dose 3D CT imaging reconstruction.

Description: Advertisement: IEEE.

Description: Advertisement: IEEE.

Description: To increase contrast in positron emission tomography (PET) images, researchers are investigating detectors that reach below the nanosecond timing resolution. This allows a tight coincidence window which reduces random coincidence counts in the acquired data, as well as to include time-of-flight information into the reconstruction algorithms. With this goal in mind, single photon avalanche diode (SPAD) arrays have been under study for their excellent timing performances. However, their spurious dark counts can blur the start of PET signals where timing information is the most precise and create false starts in the acquisition system, introducing dead time. To minimize these problems in digital SPAD systems using a single time to digital converter (TDC) per PET channel, dark count discriminator circuits are required to reduce timing errors and increase the triggering efficiency in presence of dark counts. This paper compares the performance of a probabilistic and a novel delay line based dark count discriminator. Simulations of a SPAD array investigate the impact of dark counts on triggering efficiency and coincidence timing. Results show that the probabilistic discriminator provides excellent event recovery with regard to dark counts at the cost of some coincidence timing resolution. On the other hand, the delay line discriminator maintains the peak coincidence timing resolution but does not provide as much efficiency at high dark count rate levels.

Description: The imminent closure of NRU reactor in Canada and HFR reactor in Holland threatens $sim 70% $ of the world’s supply of $^{{99}{rm m}}{rm Tc}$ used in over 30 million medical applications yearly. Researchers around the globe are investigating alternative methods of production, mainly using accelerators. This paper presents a concept feasibility study of a novel technique dubbed nSPECT, in which non-radioactive isotopes administered to patients would be activated with slow neutrons to emit prompt gamma rays (PGNA). Although a common technique of elemental analysis, PGNA has not been used for medical imaging. This paper presents SPECT images of $^{131}{rm I}$ at activity levels that could be reasonably produced by neutron activation of $^{149}{rm Sm}$ in vivo. Simulated Compton noise from hydrogen was added to degrade the images to levels that would be expected in practice. Advantages of nSPECT are discussed. This concept feasibility study suggests that nSPECT might provide an alternative means for medical imaging should the accelerator-based methods fail to make sufficient quantities of $^{{99}{rm m}}{rm Tc}$ .

Description: Provides instructions and guidelines to prospective authors who wish to submit manuscripts.

Description: This paper presents a novel multichannel time to digital converter (TDC) specifically designed for the digitization of photon time of flight (TOF) and energy in positron emission tomography (PET) scanners. A coarse-fine architecture based on a counter combined with a delay locked loop (DLL) is implemented using a fully synchronous approach exploiting the pipeline principle and dynamic logic. This makes the design particularly compact and suitable for multichannel applications. The converter is also able to reject the events generated by the dark noise of the photodetectors used in the PET modules. This significantly reduces the communication bandwidth required for reading the TDC outputs. The TDC has been designed in a 65 nm CMOS process and features 8 channels that provide the arrival time information of an event with an LSB of 102 ps. The core occupies an active area of $0.3~hbox{mm}^2$ and consumes 230 mW.

Description: Multi-voltage threshold (MVT) digitization, which has been implemented in our preclinical scanner–Trans-PET BioCaliBurn, is a low-power sampling solution with a reasonable cost for fast scintillation pulses. This MVT digitizing scheme employs a few comparators with programmable reference voltages for determining the time points when the scintillation pulse crosses the user-defined voltage thresholds. After obtaining the digital time samples, use of various sophisticated linear or nonlinear algorithms to improve the accuracy of timing information becomes possible. In the previous implementation of MVT digitizers, the arrival time of a scintillation pulse was determined by the linear fitting (LF) algorithm, which assumes leading edge as a straight line, and not involves the transition time on the falling edge. It is not unreasonable to expect achieving a better timing resolution in MVT-based PET detectors by the combinatorial optimization of MVT samples both on leading and falling edges. In this paper, a novel method, referred to as quadratic programming (QP) method is therefore proposed to mark the time stamps of sampling event pulses. In this method, the arrival time is directly expressed as a parametric combination of the MVT samples. The parameters in the combination are obtained by the quadratic programming which minimizes variation of timing error. To evaluate the performance of QP/MVT method and other time pickoff methods, we setup two gamma ray detectors using $LaBr_{3}:Ce$ crystal and Hamamatsu R9800 PMT. The scintillation pulses are directly read out by Tektronics DPO 71604 digital storage oscilloscope. CTR of 175 ps was obtained by QP/MVT, and 191 ps by LF/MVT, when four thresholds were employed in each of the two channels. The experimental results indicate the potential advantage of QP/MVT in timing determination. Meanwhile, the assumption of linear leading edge, wh- ch is the basis of LF method, was demonstrated to be improper in the data analysis. For QP method, probably of even greater significance is the manner to define the parameters rather than the resulting detector-specified parameters.

Description: The current ATLAS Tile Calorimeter read-out system is scheduled for replacement around 2023 due to old age and higher performance needs. The new proposed system is designed to be radiation tolerant, modular, redundant and reconfigurable. To achieve full detector read-out, Kintex-7 FPGAs from Xilinx will be used, in addition to multiple 10 Gb/s optical read-out links. During 2015/2016, a hybrid demonstrator system including the new read-out system will be installed in one slice of the ATLAS Tile Calorimeter to evaluate the new design. This paper describes different firmware strategies along with their integration in the demonstrator in the context of high reliability protection against hardware malfunction and radiation induced errors.

Description: We propose a new fixed latency scheme for Xilinx gigabit transceivers that will be used in the upgrade of the ATLAS forward muon spectrometer at the Large Hadron Collider. The fixed latency scheme is implemented in a 4.8 Gbps link between a frontend data serializer ASIC and a packet router. To achieve fixed latency, we use IO delay and dedicated carry in resources in a Xilinx FPGA, while minimally relying on the embedded features of the FPGA transceivers. The scheme is protocol independent and can be adapted to FPGA from other vendors with similar resources. This paper presents a detailed implementation of the fixed latency scheme, as well as simulations of the real environment in the ATLAS forward muon region.

Description: This work describes the development of a gamma detector based on silicon drift detectors (SDDs) to read out large ${hbox{LaBr}}_3$ : ${hbox{Ce}}$ scintillators for gamma-ray astronomy applications, within an activity supported by the European Space Agency (ESA). SDDs, characterized by high quantum efficiency and low electronic noise, when coupled with a scintillator are good candidates for gamma-ray spectroscopy applications in a wide energy range, e.g., from 150 keV to 15 MeV. The gamma-ray detector prototype presented here is composed of a 2 ${^prime}{^prime}$ $times$ 2 ${^prime}{^prime}$ ${hbox{LaBr}}_3$ : ${hbox{Ce}}$ scintillator coupled with four SDD arrays arranged in a $2 times 2$ format (a total of 36 SDDs). This detection system is operated with custom readout application specific integrated circuits (ASICs) and a data acquisition (DAQ) system. With this prototype gamma-camera, an energy resolution of 3.4% FWHM at 662 keV has been measured. Spectroscopy measurements have been carried out between 300 keV and 1800 keV and the achieved results are consistent with the electronic noise of the SDD technology. In this work, we report on the SDD based detection head’s design, its X-ray characterization, readout electronics, experimental setups and gamma-ray spectroscopy results. Finally, perspectives with the possible use of an improved SDD technology are discussed.

Description: The probability of large-angle scattering for multi-GeV muons in lead targets with a thickness of ${cal O}{(10^{ - 1}})$ radiation lengths is studied. The new estimates presented here are based both on simulation programs (GEANT4 libraries) and theoretical calculations. In order to validate the results provided by simulation, a comparison is drawn with experimental data from the literature. This study is particularly relevant when applied to muons originating from ${nu_{mu}}$ CC interactions of CNGS beam neutrinos. In that circumstance the process under study represents the dominant background for the ${nu_{mu}} rightarrow {nu _tau }$ search in the $tau rightarrow mu $ channel for the OPERA experiment at LNGS. Finally we also investigate, in the CNGS context, possible contributions from the muon photo-nuclear process which might in principle also produce a large-angle muon scattering signature in the detector.