ALBERT

Description: Providing information about the leak flow rate caused by a loss-of-coolant accident (LOCA) to nuclear power plant (NPP) operation personnel is a key to the management and mitigation of severe post-LOCA circumstances at NPPs where active safety injection systems do not actuate. The leak flow rate is a function of break size, differential pressure (i.e., difference between internal and external reactor vessel pressure), temperature, and so on. In this study, the break position and size were first identified and predicted, and then, the leak flow rate was predicted using a fuzzy neural network (FNN). The FNN was developed using training data and validated using independent test data. The data were generated from simulations of the optimized power reactor 1000 (OPR1000) using MAAP4 code. The data for training the FNN model were selected among the acquired data using the subtractive clustering method, and FNN performance was improved. The developed FNN model was sufficiently accurate to be used for predicting leak flow rate, which is useful information for managing severe post-LOCA situations.

Description: The gigabit laser driver (GBLD) and low-power GBLD (LpGBLD) are two radiation-tolerant laser drivers designed to drive laser diodes at data rates up to 4.8 Gb/s. They have been designed in the framework of the gigabit-transceiver (GBT) and versatile-link projects to provide fast optical links capable of operation in the radiation environment of future high-luminosity high-energy physics experiments. The GBLD provides laser bias and modulation currents up to 43 mA and 24 mA, respectively. It can thus be used to drive vertical cavity surface emitting laser (VCSEL) and edge-emitting laser diodes. A pre-emphasis circuit, which can provide up to 12 mA in 70 ps pulses, has also been implemented to compensate for high external capacitive loads. The current driving capabilities of the LpGBLD are 2 times smaller that those of the GBLD as it has been optimized to drive VCSELs in order to minimize the power consumption. Both application-specific integrated circuits are designed in 0.13 $~mu$ m commercial complementary metal–oxide semiconductor technology and are powered by a single 2.5 V supply. The power consumption of the core circuit is 89 mW for the GBLD and 55 mW for the LpGBLD.

Description: This paper presents a new SEU-tolerant latch design based on Quatro and NMOS feedback transistors. By using these feedback transistors, the SEU susceptibility is decreased because of the cutoff feedback loop. Simulation results demonstrate that the proposed design is immune to static single node upsets. The proposed latch and the reference Quatro were designed and fabricated on a 130 nm process. The test chip was exposed to heavy ions at the TAMU Cyclotron facility. The testing results show that the proposed design has a higher upset LET threshold and lower cross-section when compared to the reference latch. Its lower SEU vulnerability comes with small area penalty.

Description: This paper provides a detailed description of the Energetic Particle Telescope (EPT) accommodated on board the PROBA-V satellite launched on May 7th, 2013 on a LEO, 820 km altitude, 98.7 $^circ $ inclination and a 10:30–11:30 Local Time at Descending Node. The EPT is an ionizing particle spectrometer that was designed based on a new concept and the most advanced signal processing technologies: it performs in-flight electron and ion discrimination and classifies each detected particle in its corresponding physical channels from which the incident spectrum can be readily reconstructed. The detector measures electron fluxes in the energy range 0.5–20 MeV, proton fluxes in the energy range 9.5–300 MeV and He-ion fluxes between 38 and 1200 MeV. The EPT is a modular configurable instrument with customizable maximum energy, field of view angle, geometrical factor and angular resolution. Therefore, the features of the currently flying instrument may slightly differ from those described in past or future configurations. After a description of the instrument along with the data acquisition and analysis procedures, the first particle fluxes measured by the EPT will be shown and discussed. The web-site located at http://web.csr.ucl.ac.be/csr_web/probav/ which daily displays measured fluxes and other related studies will also be briefly described.

Description: Dynamic random access memory (DRAM) data retention time degradation induced by radiation exposure is investigated in this paper. We present the experimental setup and the results of total ionizing dose (TID) test on a COTS SDRAM device. We observed a significant retention time reduction related to the absorbed dose and we assume radiation induced interface trap generation as the origin of the retention time reduction. By measuring individual cells retention time before and after radiation exposures, we found out that the reduction is not homogeneous among cells: the amount of leakage current increase depends on the position and the energy level of the generated trap, leading to a wide distribution of retention time reduction. Of particular interest is the fact that device was unbiased during irradiation and that no post-irradiation recovery was observed.

Description: A serpentine transmission-line in a microstrip configuration is used to enable fine position sensing in semiconductor radiation detectors. Specifically demonstrated with silicon substrates coupled to standard charge-sensitive preamplifiers, a meandering electrode is used to enable lateral position sensing to within an approximately 1 cm length along the electrode. Configured in a rectilinear shape, the lateral resolution is therefore equivalent to the strip pitch, which we have made as small as $4 ~muhbox{m}$ . The position-of-interaction is extracted using either timing or amplitude techniques, both enabled by the slow-wave propagation structure inherent to the standard metal-semiconductor-insulator configuration of the bounding electrodes, the analysis of which is summarized and compared experimentally.

Description: We developed a field-programmable gate array (FPGA) TDC module for the tracking detectors of the Fermilab SeaQuest (E906) experiment, including drift chambers, proportional tubes, and hodoscopes. This 64-channel TDC module had a 6U VMEbus form factor and was equipped with a low-power, radiation-hardened Microsemi ProASIC3 Flash-based FPGA. The design of the new FPGA firmware (Run2-TDC) aimed to reduce the data volume and data acquisition (DAQ) deadtime. The firmware digitized multiple input hits of both polarities while allowing users to turn on a multiple-hit elimination logic to remove after-pulses in the wire chambers and proportional tubes. A scaler was implemented in the firmware to allow for recording the number of hits in each channel. The TDC resolution was determined by an internal cell delay of 450 ps. A measurement precision of 200 ps was achieved. We used five kinds of tests to ensure the qualification of 93 TDCs in mass production. We utilized the external wave union launcher in our test to improve the TDC’s measurement precision and also to illustrate how to construct the Wave Union TDC using an existing multi-hit TDC without modifying its firmware. Measurement precision was improved by a factor of about two (108 ps) based on the four-edge wave union. Better measurement precision (69 ps) was achieved by combining the approaches of Wave Union TDC and multiple-channel ganging.

Description: By measuring the time of flight of scattered X-ray photons, the point of interaction, assuming a single scatter, can be determined, providing 3-D information about an object under inspection. This paper describes experimental ToF Compton scatter measurements conducted at the versatile electron linear accelerator (VELA), a picosecond pulsewidth electron source situated in Daresbury, U.K. The ToF of scattered X-ray photons was measured using a CeBr3 detector, and a full width at half maximum (FWHM) of between 29  and 36 cm was achieved with a 5-cm-thick plastic test object. By implementing a low-energy cutoff, the FWHM was reduced to between 12 and 26 cm. Two test objects placed in series with a 50-cm space between were separable in the data after applying the low energy cutoff.

Description: This work describes in detail the Radiation Hardness Assurance methodology applied to the development of new radiation tolerant power converter control system for the Large Hadron Collider at the European Organization for Nuclear Research (CERN). This system is based primarily on commercial-off-the-shelf components for which the extensive testing scheme is applied to decrease the probability of radiation failures during the operation of the LHC machine in the high-luminosity operating conditions era.

Description: As it is planned to switch the heavy-ion synchrotron SIS18 from single- to dual-harmonic cavity operation after construction of the new Facility for Antiproton and Ion Research (FAIR), its closed-loop control system for the damping of coherent longitudinal oscillations needs an appropriate adjustment. To damp dipole oscillations, the phase shift, applied by the control system to the first cavity voltage (running with harmonic number ${h_1}$ ) has to be doubled for the second cavity (running with double frequency and harmonic number ${h_2} = 2 cdot {h_1}$ ). Furthermore, the dipole oscillation frequency can no longer be estimated by linearization of the applied voltage like it is done in a single-harmonic cavity setting. In a dual-harmonic cavity setting as it is presented here, the dipole oscillation frequency depends nonlinearly on the bunch length. The control loop is closed by a digital signal processor, an optical splitter, and direct digital synthesizers. This paper describes the control loop and its theoretical background, and presents measurement results. In addition, simulation results and theoretical predictions are given, which are all in good agreement. Furthermore, optimal filter parameter settings are derived.

Description: In this paper, we describe the whole process of designing and manufacturing an 83.2 MHz, three-stage radio frequency (RF) amplifier for a SKKUCY-9 cyclotron. It consisted of a preamplifier, intermediate power amplifier (IPA), and power amplifier (PA) stage. The maximum power value for each stage is 0.05 kW, 1.5 kW, then 20 kW RF power. Formula calculation, circuit design, and electromagnetic analysis were implemented in the RF amplifier design. Along with the power stage and anode power supply, an RF amplifier control system for the RF amplifier was developed. After design and manufacturing, we conducted impedance matching measurements with a network analyzer to achieve $50Omega $ for the IPA and PA. Finally, we analyzed the RF amplifier characteristics by implementing RF testing with both a dummy load and a RF coupler. The expected and measured RF characteristics were in agreement, and a detailed analysis is described.

Description: A transmission particle detector based on a super-thin diamond membrane film which can also be used simultaneously as a vacuum window for ion beam extraction has been developed. Charge collection characteristics of a $6.8~mu{hbox{m}}$ -thick diamond membrane detector for high-energy heavy ions including 75 MeV Ne, 150 MeV Ar, 322 MeV Kr, and 454 MeV Xe have been investigated for the first time. Charge collection signals under single particle flux from the thin part are stable and are well distinguishable from background signals. This behavior suggests that the diamond membrane detector could be used for counting single ions. On the other hand, charge collection efficiency is found to decrease with increasing of charge generated in the diamond membrane detector. This suggests that the pulse height defect, which has been previously reported for Si and SiC detectors, also occurs in the diamond membrane detector.

Description: A novel, multi-point contact high-purity germanium detector has been developed for applications in high-rate gamma environments. The planar detector was fabricated with seven point contacts, a high-voltage steering grid and bias electrode using amorphous germanium technology. We have characterized this detector and report herein on the depletion profile, leakage current, energy resolution, and charge-sharing behavior.

Description: We present the design and fabrication of a 2D monolithic pixelated detector array using metalorganic vapor-phase epitaxy grown thick CdTe epitaxial layers on Si substrates. Each pixel in the array consists of a ${rm p-CdTe/n-CdTe/n}^{+}-{rm Si}$ heterojunction diode structure, and pixels were patterned by cutting deep vertical grooves using a dicing saw. We also developed a low-temperature conductive-epoxy based bonding technique to bond the array to the read out electronic circuit via an interface board. Preliminary evaluation shows that the fabricated array is capable of discriminating energies of the incident radiation and can be applied for the energy discriminating imaging purpose. Moreover, this fabrication technique is useful in developing larger imaging arrays.

Description: The time over threshold (TOT) method has several advantages over direct pulse height analysis based on analog to digital converters (ADCs). A key advantage is the simplicity of the conversion circuit which leads to a high level of integration and a low power consumption. The TOT technique is well suited to build multi-channel readout systems for pixelated detectors as described in our previous work that also exploits the Pulse Width Modulation (PWM) method. The main limitation of the TOT technique is that the relation between the input charge to be measured and the width of the encoded pulse is strongly non-linear. Dynamic range limitation is also an issue. To address these aspects, we propose a new time over threshold conversion circuit where the threshold of the comparator is dynamically changed instead of being constant. We call this scheme the “dynamic TOT method”. We show that it improves linearity and dynamic range. It also shortens the duration of measured pulses leading to higher counting rates. We present a short analysis that explains how the ideal linear input charge to TOT transfer function can theoretically be obtained. We describe the results obtained with a test circuit built from discrete components and present several of the spectrums obtained with crystal detectors and a radioactive source. The proposed method can be used for applications like Positron Emission Tomography (PET) that require moderate energy resolution.

Description: The objective of this paper is to describe a Switcher ASIC with 64 high voltage output channels. Each channel provides two high voltage control pulses with maximum amplitudes of 32 V. The high voltage level shifter was designed with a current mirror switching circuit that has a readily adjustable switching speed, unlike conventional switching circuits. The logic control circuit uses a forward and reverse chain of Flip-Flops along with other combinational logic gates to generate bidirection sequential control pulses with adjustable pulsewidth and polarity. The layout was carefully designed to achieve a 14 $mu$ m width for the last stage transistors' drain path based on the 50 $mu$ m output channel pitch set up. At least a 200 mA current driving capability was obtained for each channel. The design was fabricated using TSMC's 180 nm CMOS HV technology. The paper further discusses the critical design steps including chip architecture, layout, simulation and bench test. The final experimental results demonstrate that the Switcher ASIC meets requirements and the rising time could reach 480 ns with a 1 nF capacitive load at 15 V pulse amplitude. With this load, the total power consumption of the chip was measured to be approximately 4 mW when the input clock period was 42.2 $mu$ s. In addition to use in a charge-pump detector, the ASIC can be used to control the charge accumulation and readout in other detectors, such as X-ray pump probe detectors (XPP).

Description: Online nuclear measurements inside experimental channels of material testing reactors (MTRs) are needed for experimental works (to design mock-ups) and for numerical works (input data) in order to better understanding complex phenomena occurring during the accelerated ageing of materials and the irradiation of nuclear fuels. In this paper, we focus only on one kind of measurements: nuclear heating performed by means of a radiometric calorimeter. The aims of numerical and experimental works are firstly to optimize the sensor response: in particular the sensitivity for new energy deposit ranges (new lower nuclear heating level in the reflector), and then to miniaturize and adapt this sensor for irradiation conditions in the Jules Horowitz Reactor (JHR). A calorimeter, developed previously by the CEA, is studied. It corresponds to a graphite differential calorimeter. It is used with a nonadiabatic mode called heat flow mode too. Experimental calibration of the sample cell is presented. In that case, energy deposit is simulated by Joule effect and the sample cell is inserted into a bath at a regulated temperature and controlled flow. The response of the sensor is discussed versus electrical power imposed for two flow rates. Numerical works show the influence of the gas conductivity and of specific dimensions on the cell sensitivity.

Description: This paper deals with the effects of $^{60}$ Co gamma irradiation on punch-through commercial insulated gate bipolar transistors turn-off switching behavior. The response of the threshold voltage, the gate-emitter leakage current, the collector leakage current, the collector-emitter breakdown voltage and the turn-off switching parameters under three different in situ gate biases are described. Charge trapping in the gate oxide causes the decrease of the threshold voltage. It is shown that the decrease of this parameter and the modifications in the Miller plateau level and width result in an increase of the turn-off delay time, the collector current fall-time, the collector-emitter voltage rise-time, and consequently an increase of the turn-off switching losses and a decrease of the turn-off overshoot collector-emitter voltage.

Description: The GUINEVERE (Generation of Uninterrupted Intense NEutron pulses at the lead VEnus REactor) project was launched in 2006 within the framework of FP6 EUROTRANS in order to validate online reactivity monitoring and subcriticality level determination in accelerator driven systems (ADS). Therefore, the VENUS reactor at SCK•CEN in Mol, Belgium, was modified towards a fast core (VENUS-F) and coupled to the GENEPI-3C accelerator built by CNRS. The accelerator can operate in both continuous and pulsed mode. The VENUS-F core is loaded with enriched Uranium and reflected with solid lead.

Description: Novel techniques to measure induced fissions in spent fuel after re-irradiation at low power have been developed and tested at the Proteus zero-power research reactor. The two techniques are based on the detection of high energy gamma-rays emitted by short-lived fission products and delayed neutrons.

Description: This paper represents the first attempt to discuss the use of an artificial single-crystal diamond as a new microdosimeter. The Diamond MicroDosimeter (DMD) detecting region is a thin layer of highly controlled thickness $(〈 5~mu {rm m})$ and high purity intrinsic monocrystalline diamond grown over a backing boron doped monocrystalline diamond. This viable, small, compact and user-friendly device is able to obtain spectra of the energy deposition in sensitive volumes of the order of micrometer. The paper reports the first experimental tests performed to measure the dose distribution in terms of lineal energy and the simulation performed by the Monte Carlo code FLUKA to optimize the design of the new DMD. Advantages and shortcomings of the DMD are discussed.

Description: A prototype 1mm thick CdTe detector bonded to a Timepix chip with 256*256 pixels at 55 $mu$ m pitch was evaluated for use as a photon-counting imaging detector at high energy synchrotron beamlines (energy range 30–100 keV). A complete characterization of the system was performed. Powder diffraction experiments have also been conducted using a monochromatic beam at the ESRF. The expected gain in efficiency at energies above 30 keV with reference to silicon pixel detectors and current CCD systems of similar pixel size was demonstrated, together with an improved spatial resolution. Background-free powder diffraction spectra were obtained using the Timepix energy thresholding feature. The energy-resolved detection capabilities are limited by a strong charge sharing. The major limitations preventing a wider use of these devices at synchrotron X-ray sources are the lack of homogeneity of the CdTe crystal which exhibits numerous defects, and the unavailability of large fields of view.

Description: This paper reports about the performances of single crystal diamond (SCD) detectors operated at high temperature (up to 200 $^{circ}$ C) and irradiated with alpha particles. Two different types of SCD detectors were studied: a) SCD of commercial type; b) SCD produced at Rome “Tor Vergata” University and characterized by a layered structure.

Description: In many modern applications based on detected radiation measurements, high rate and high resolution are more and more features of primary importance. In this scenario, it is well known that high resolution of measurements and high rate of pulses are conflicting issues, which implies a trade-off between live time of the system and precision of measurements. We propose a digital processing technique based on adaptive filters for maximizing both achievable resolution and sustainable rate.

Description: The current mode line terminating input stage of an integrated circuit for the upgrade of the LHCb calorimeter front end electronics is presented. The circuit is based on a current mode input stage followed by two fully differential interleaved channels, namely a switched integrator and a track and hold. The input stage employs a novel electronically cooled input termination scheme to achieve stringent noise requirements. Compared to previous designs, its novelty relies in the use of two current feedback loops to decrease and control the input impedance of a common base stage. Two prototypes in Austriamicrosystems SiGe BiCMOS 0.35 $mu$ m technology have been designed and tested. Key measurements have been performed. Reflection coefficient is smaller than 0.5% for the full dynamic range, which is 12 bits. Relative linearity error is below 1%. Output noise is about 1 LSB after applying correlated double sampling.

Description: Charge amplifiers represent the standard solution to amplify signals from capacitive detectors in high energy physics experiments. In a typical front-end, the noise due to the charge amplifier, and particularly from its input transistor, limits the achievable resolution. The classic approach to attenuate noise effects in MOSFET charge amplifiers is to use the maximum power available, to use a minimum-length input device, and to establish the input transistor width in order to achieve the optimal capacitive matching at the input node. These conclusions, reached by analysis based on simple noise models, lead to sub-optimal results. In this work, a new approach on noise analysis for charge amplifiers based on an extension of the $g_{m}/I_{D}$ methodology is presented. This method combines circuit equations and results from SPICE simulations, both valid for all operation regions and including all noise sources. The method, which allows to find the optimal operation point of the charge amplifier input device for maximum resolution, shows that the minimum device length is not necessarily the optimal, that flicker noise is responsible for the non-monotonic noise versus current function, and provides a deeper insight on the noise limits mechanism from an alternative and more design-oriented point of view.

Description: The Mercury imaging X-ray spectrometer (MIXS) on board of ESA's fifth cornerstone mission BepiColombo will be the first space instrument using DEpleted P-channel FET (DEPFET) based detectors. The MIXS spectrometer comprises two channels with identical focal plane detectors and is dedicated to energy resolved imaging of X-ray fluorescence from the mercurial surface.

Description: Numerical simulations of thermoelectric effect spectroscopy (TEES) and photo-induced transient current spectroscopy (PICTS) in CdTe were performed with the aim to interpret experimental results and to look for possibilities to obtain credible information about trap capture cross-sections. The TEES and PICTS spectra were calculated by solving kinetic equations. Trap energy and capture cross section were determined by variable heating rate and double gate methods and compared with input data. Deviation of the established capture cross-section from the input value was demonstrated for the strong retrapping. It was concluded that the trap capture cross-section, especially if obtained anomalously low, might be incorrect due to invalid premises of models, which neglect retrapping. The possibility to acquire an information about trap properties from the shape or magnitude of glow curves was checked. It was demonstrated that the magnitude of TEES signal corresponding to slow or fast retrapping depends unequally on the initial optical excitation.

Description: The peak energy resolution of germanium detectors deteriorates with increasing neutron fluence. This is due to hole capture at neutron-created defects in the crystal which prevents the full energy of the gamma-ray from being recorded by the detector. A phenomenological model of coaxial HPGe detectors is developed that relies on a single, dimensionless parameter that is related to the probability for immediate trapping of a mobile hole in the damaged crystal. As this trap parameter is independent of detector dimensions and type, the model is useful for predicting energy resolution as a function of neutron fluence.

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

Description: The ATLAS silicon tracker community foresees an upgrade from the present octafluoropropane $({rm C}_{3}{rm F}_{8})$ evaporative cooling fluid to a composite fluid with a probable 10–20% admixture of hexafluoroethane $({rm C}_{2}{rm F}_{6})$ . Such a fluid will allow a lower evaporation temperature and will afford the tracker silicon substrates a better safety margin against leakage current-induced thermal runaway caused by cumulative radiation damage as the luminosity profile at the CERN Large Hadron Collider increases. Central to the use of this new fluid is a new custom-developed speed-of-sound instrument for continuous real-time measurement of the ${rm C}_{3}{rm F}_{8}/{rm C}_{2}{rm F}_{6}$ mixture ratio and flow. An acoustic vapour mixture analyzer/flow meter with new custom electronics allowing ultrasonic frequency transmission through gas mixtures has been developed for this application. Synchronous with the emission of an ultrasound ‘chirp’ from an acoustic transmitter, a fast readout clock (40 MHz) is started. The clock is stopped on receipt of an above threshold sound pulse at the receiver. Sound is alternately transmitted parallel and anti-parallel with the vapour flow for volume flow measurement from transducers that can serve as acoustic transmitters or receivers. In the development version, continuous real-time measurement of ${rm C}_{3}{rm F}_{8}/{rm C}_{2}{rm F}_{6}$ flow and calculation of the mixture ratio is performed within a graphical user interface developed in PVSS-II, the Supervisory, Control and Data Acquisition standard chosen for LHC and its experiments at CERN. The described instrument has numerous potential applications—including r- frigerant leak detection, the analysis of hydrocarbons, vapour mixtures for semi-conductor manufacture and anesthetic gas mixtures.

Description: Transient-current technique was used for measuring the profile of the electric field in CdTe and CdZnTe samples excited by an $^{bf 241}{hbox{Am}}~{bf alpha}$ -particle source. Current waveforms were analyzed by a general model, which involved both the effect of the space charge in the depleted region and charge trapping. The carrier mobility and the electric-field profile were also evaluated in this way. The maximum electric field was observed close to the cathode, whereas the minimum occurred near the anode. The decrease in the strength of the electric field from cathode to anode was explained in terms of a positive space charge formed in the detector's volume. Measurements under incomplete depletion, when an “inactive” region with zero electric field was observed under the anode, were reported as well. Space-charge densities of ${bf 10^{11}}$ – ${bf 10^{12}}~{hbox{cm}}^{bf -3}$ in CdTe and ${bf 10^{10}}~{hbox{cm}}^{bf -3}$ in CdZnTe were evaluated. The dynamics of electron–hole plasma formed by a single ${bf alpha}$ -particle absorption event was analyzed in detail and used as a complementary test of our reported model. An excellent agreement with theory was obtained.

Description: The influence of monochromatic optical stimulation with wavelengths from 400 to 1100 nm on the characteristics of CdZnTe quasi-hemispherical detectors was studied. It was found that illumination with infrared (IR) light with wavelengths of 870–900 nm close to the absorption edge of the CdZnTe significantly improves the performance of the detector at room temperature. Improvement can be achieved with low-intensity IR illumination at 1–300 $mu{hbox {W}}$ depending on the chosen wavelength of illumination. Higher intensity illumination was observed to lead to the degradation of the detector's spectrometric characteristics. IR radiation was noted to influence the detector's sensitivity, changing the equilibrium between free and trapped carriers and improving charge collection. For practical purposes, the use of an IR light-emitting diode (LED) as the IR source is suggested. We tested various LEDs with light wavelengths of 770 to 1020 nm. The degree of improvement was different for different detectors due to the different source materials used in the detectors and their dimensions. For example, the performance of a detector that was 10 mm $times,$ 10 mm $times,$ 5 mm in size with an initial energy resolution (FWHM) of 14.9 keV at 662 keV was improved with an IR LED illumination of up to 8.6 keV. IR stimulation improved the spectrometric characteristics for a wide range of energies starting at 59.6 keV without decreasing detection efficiency and over the temperature range from ${- 30}^{circ}{hbox {C}}$ to ${+ 70}^{circ}{hbox {C}}$ . We found that the use of IR illumination with a properly chosen wavelength not only imp- oves the performance of detectors at low temperatures but also stabilizes them over time.

Description: We introduce a fast pulse sampling module with the use of switched-capacitor arrays (SCAs). The module is in the size of 3U for PCI extensions for Instrumentations (PXI), and there are a total of six channels with a sampling rate of up to 5 giga samples per second (GS/s) per channel. With this module, we evaluate the issues of fast pulse timing from reconstructed waveform, as well as the scheme of interleaved sampling between adjacent channels within the module. The timing precision of this module is proved to be below 10 ps RMS at 4.7 GS/s after a series of calibration strategies. We have also achieved 9.4 GS/s with two channels interleaved on board.

Description: The ionic conductivity of TlBr, TlI and their solid solutions, candidates for high energy radiation detection, was examined using impedance spectroscopy. The orthorhombic to cubic phase change in TlI was observed via a steep change in conductivity with increasing temperature, whereas the TlBr-TlI solid solution was cubic throughout the measured temperature range, in agreement with the literature. The intrinsic conductivity of the cubic phase of each material showed nearly identical behavior, indicating that I substitution for Br has little to no effect on the combined defect formation and transport parameters in the studied range. Additionally, optical transmission was correlated with I concentration.

Description: This paper proposes a 128-channel column-parallel two-stage time-to-digital converter (TDC) utilizing a time difference amplifier (TDA) and shows measurement results obtained from an implementation in a 0.35- $mu$ m CMOS process. The first stage operates as a coarse TDC, the time residue is amplified by a TDA, then converted by the second-stage TDC. As the gain of the time difference amplifier can be adjusted from 8.5 to 20.4, the time resolution of the TDC can be tuned from 21.4 to 8.9 ps. The time resolution variation due to process-voltage-temperature (PVT) effects is $pm$ 5.8% without calibration when the time resolution is 12.9 ps. We propose a calibration method to compensate LSB changes due to the power supply fluctuation and temperature variation.

Description: The CERN-EU High Energy Reference Field (CERF) facility is used in the calibration of neutron dosimeters for radiation protection applications in aviation and high energy physics. A comparison of the facility's microdosimetric spectra obtained with a new Silicon on Insulator (SOI) Microdosimeter and a HAWK Tissue Equivalent Proportional Counter (TEPC) is presented. Experimental data obtained with both devices indicates the presence of a small charged particle flux within the neutron dominated field which makes a non negligible contribution to the dose equivalent.

Description: Electromagnetic (EM) fields near the beam axis in a radio frequency quadrupole (RFQ) are very sensitive to dimensional changes especially on vane tip geometries. Due to measurement difficulties, field distribution around the beam axis is generally assumed to be equal to that measured outside of vane gaps in quadrants using a bead-pull technique. If an RFQ structure has any mechanical imperfections in its vanes, local field distributions around the beam axis could be different from the design field profiles. The distorted field may affect beam quality as well as the operational stability and reliability of the RFQ system. In order to understand changes of field distribution in the RFQ against localized mechanical imperfections, a study with systematic 3D simulations has been carried out using a model developed for the RFQ in Spallation Neutron Source (SNS) of Oak Ridge National Laboratory. Field information at various locations such as around the beam-axis, bead-pull positions, and pickup probe positions are investigated with the vane tip perturbations. Design considerations for proper field retuning with perturbation are also presented and discussed to help future RFQ designs.

Description: The Gamma Ray Energy Tracking In-Beam Nuclear Array (GRETINA), a germanium detector system capable of measuring energy and position (within better than 2 mm rms) of gamma-ray interaction points and tracking multiple gamma-ray interactions, has been built. GRETINA is composed of seven detector modules, each with four high purity germanium crystals. Four custom designed electronics support the operation of the detectors: Digitizer/Digital Signal Processing (DSP), Trigger/Timing, Breakout Chassis and the Detector Interface Box. The Digitizer/DSP converts the analog information with 14-bit analog to digital converters operating at 100 MS/s, and digitally processes the data to determine the energy and timing information of the gamma interactions within a crystal. The computing system is composed of VME readout CPUs running VxWorks, which communicate with 62 dual-processor farm (each processor with four cores) through a 10 Gb/s Ethernet switch. The CPUs read out the digitizer/DSPs and send the data to the farm. The processors compute the position and track of the interactions of the gamma-ray inside the crystals. The processor farm is capable of processing in real-time the position of 20 000 gamma-ray/s. In this paper we will present the details of the implementation and performance of the electronics and computing system of GRETINA.

Description: A pulse-width locked loop (PWLL) circuit is reported that compensates for process, voltage, and temperature (PVT) variations of a linear ramp generator within a 12-bit multi-channel Wilkinson (single-slope integrating) Analog-to-Digital converter (ADC). This PWLL was designed and fabricated in a 0.5- $mu$ m Silicon Germanium (SiGe) BiCMOS process. Simulation and silicon measurement data are shown that demonstrate a large improvement in the accuracy of the PVT-compensated ADC over the uncompensated ADC.

Description: Resistive switching properties of valence change memory (VCM) resistive-random-access-memory (ReRAM) devices (TiN/HfO $_{2}$ /TiN) are investigated after exposure to proton radiation with total ionizing doses (TID) of 1.5, 3, and 5 Grad(Si) and compared to similar measurements from electrochemical metallization memory (ECM) ReRAM devices (Pt/HfO $_{2}$ :Cu/Cu). The TiN/HfO $_{2}$ /TiN ReRAMs show significantly superior TID radiation-hardness compared to Pt/HfO $_{2}$ :Cu/Cu ReRAMs: 1) All devices remained functional after radiation; 2) switching parameters including average $V_{rm set}$ , $V_{rm reset}$ , $R_{rm on}$ , $R_{rm off}$ showed minimal or no degradation; and 3) TID radiation enhanced the uniformity of resistive switching among all VCM devices. The superior radiation responses of the VCM ReRAM devices relative to ECM ReRAMs result from the distinct conduction filament (CF) formation mechanisms. For the VCM ReRAM system, the radiation-induced vacancy density does not serve to inhibit the trap-assisted tunneling associated with the Hf-rich CF formation kinetics. On the contrary, vacancy-promoted charge trapping promotes VCM CF stability. In strong contrast, proton-induced vacancies for the ECM ReRAMs inhibit the formation of the metallic filament through internal field reduction due to charge trapping. The comparison of TID effects suggests that HfO $_{2}$ -based VCM ReRAMs can be m- de radiation immune to a TID up to 5 Grad(Si) and may be highly suitable for rad-hard electronics applications.

Description: The influence of thermal neutron irradiation and fast neutron irradiation on the electrical properties of AlGaN/GaN HEMTs is investigated. An increase in the drain current and a decrease in the access resistances are observed when devices are irradiated with a thermalized neutrons fluence of $4.3times 10^{10}~{rm neutrons}.{rm cm}^{-2}$ while no evolution is observed with the same fluence of fast neutrons. However, the same phenomenon is observed when the fast neutron fluence is higher $(1.8times 10^{12}~{rm neutrons.cm}^{-2})$ . AlGaN/GaN heterojunctions are analyzed by gamma spectroscopy after thermalized or fast neutron irradiations to understand the physical mechanisms induced by irradiations. In fact, we have shown that the improvement of electrical properties of devices after thermal neutrons irradiation is linked to a Ga-Ge transmutation effect. Moreover, the evolution of the drain current and access resistance when the AlGaN/GaN heterojunctions are irradiated by fast neutrons can be induced by N vacancies creation and/or a change of the strain state of the layers and/or Ga-Ge transmutation effect.

Description: A Compact Neutron Spectrometer (CNS) has been developed to measure the neutron emission spectra in Joint European Torus (JET) fusion plasma experiments. The spectrometer, based on a liquid scintillation detector (BC501A), is equipped with a Digital Pulse Shape Discrimination (DPSD) acquisition system for neutron (n) and gamma-ray $(gamma)$ separation. The CNS enables recording the n and $gamma$ pulse height spectra (PHS) up to total count rates of ${sim}10^{6}$ s $^{- 1}$ . Energy resolution, after PHS unfolding, will be ${〈}2hbox{%}$ for 14 MeV neutrons and ${〈}4hbox{%}$ for 2.5 MeV neutrons. The work done by ENEA-Frascati and Physikalisch-Technische Bundesanstalt (PTB) respectively in the assembly and test of DPSD and scintillation detector, along with the first results obtained by the spectrometer in JET plasma experiments are presented. The experience obtained with CNS in JET will contribute to the development of neutron spectrometers suitable for applications in the International Thermonuclear Experimental Reactor (ITER).

Description: As technology scales, the protection of Finite State Machines' (FSMs) states against single event upset (SEU) and multiple bit upsets (MBUs) becomes more difficult. In this paper, a self-checking approach to enhance the SEU/MBUs immunity of FSMs' states by replicating One-Hot code $M$ times for state encoding is presented. This approach can correct less than $M$ bit-flip faults in the state register per cycle. Bit-flips are treated as random events and modeled by applying Poisson distribution. Two characteristics of this approach are obtained through probability analysis: first, this approach performs better with the increase of $M$ , whereas worse when an FSM contains more states; second, this approach can offer more enhanced reliability than Binary or One-Hot state encoding with Triple Modular Redundancy (TMR). The former characteristic leads to the further improvement of this approach which is called state-reforming. The reliabilities of this proposed approach and its state-reformed solutions, as well as ${rm One mathchar"702D Hot} +{rm TMR}$ are all evaluated through simulations of fault injections.

Description: Key requirements for the practical implementation of empirical diagnostic systems are the capabilities of incremental learning of new information that becomes available, detecting novel concept classes and diagnosing unknown faults in dynamic applications. In this paper, a dynamic weighting ensembles algorithm, called ${rm Learn}^{++}.{rm NC}$ , is adopted for fault diagnosis. The algorithm is specially designed for efficient incremental learning of multiple new concept classes and is based on the dynamically weighted consult and vote (DW-CAV) mechanism to combine the classifiers of the ensemble. The detection of unseen classes in subsequent data is based on thresholding the normalized weighted average of outputs (NWAO) of the base classifiers in the ensemble. The detected unknown classes are classified as unlabeled until their correct labels can be assigned. The proposed diagnostic system is applied to the identification of simulated faults in the feedwater system of a boiling water reactor (BWR).

Description: We present optical and X-ray radiographical characterization of silica aerogels with refractive index from 1.05 to 1.07 for a Cherenkov radiator. A novel pin-drying method enables us to produce highly transparent hydrophobic aerogels with high refractive index by shrinking wet-gels. In order to investigate the uniformity in the density (i.e., refractive index) of an individual aerogel monolith, we use the laser Fraunhofer method, an X-ray absorption technique, and Cherenkov imaging by a ring-imaging Cherenkov detector in a beam test. We observed an increase in density at the edge of the aerogel tiles, produced by pin-drying.

Description: Because of its strong inherent safety, the modular high temperature gas-cooled nuclear reactor (MHTGR) has been regarded as the central part of the next generation nuclear plants (NGNPs). Power-level control is one of the key techniques which provide safe, stable and efficient operation for the MHTGRs. The physically-based regulation theory is definitely a promising trend of modern control theory and provides a control design method that can suppress the unstable part of the system dynamics and remain the stable part. Usually, the control law designed by the physically-based control theory has a simple form and high performance. Stimulated by this, a novel nonlinear dynamic output feedback power-level control is established in this paper for the MHTGR based upon its own dynamic features. This newly-built control strategy guarantees the globally asymptotic stability and provides a satisfactory transient performance through properly adjusting the feedback gains. Simulation results not only verify the correctness of the theoretical results but also illustrate the high control performance.

Description: Detailed scintillation properties of ${hbox {Sc}}_{2}{hbox {O}}_{3}$ , especially $gamma$ -ray response, are not well studied because of low density and low effective atomic number of this compound. They are reported in this paper. ${hbox {Sc}}_{2}{hbox {O}}_{3}$ single crystals grown by the micro-pulling-down method and ${hbox {Sc}}_{2}{hbox {O}}_{3}$ translucent ceramics produced by the spark plasma sintering are analyzed. Optical, luminescence, and scintillation properties of these single- and poly-crystalline solids are discussed and compared based on examination of their optical transmittance, radio-luminescence spectra, light yields under $gamma$ -ray excitation, non-proportionality, energy resolution, and scintillation decay profiles. Spectrally corrected light yields of the ${hbox {Sc}}_{2}{hbox {O}}_{3}$ single crystals and ${hbox {Sc}}_{2}{hbox {O}}_{3}$ ceramics were approximately 7,700 and 19,200 photons/MeV , respectively.

Description: The application of SRAM-based field-programmable gate arrays (FPGAs) in mission-critical systems requires error-mitigation and recovery techniques to protect them from the errors caused by high-energy radiation, also known as single event upsets (SEUs). For this, modular redundancy and runtime partial reconfiguration are commonly employed techniques. However, the reported solutions feature different tradeoffs in the area overhead and the fault latency. In this paper, we propose a low area-overhead SEU recovery mechanism and describe its application in different self-recoverable architectures, which are experimentally evaluated using a specially designed fault-emulation environment. The environment enables the user to inject faults at selected locations of the configuration memory and experimentally evaluate the reliability of the developed solutions.

Description: We investigated the response linearity and the energy resolution of a silicon based reach-through avalanche photodiode (APD) for low energy ions ranging from 5 keV to 250 keV. We found that space charge affects the APD gain, and that this could be compensated by applying a simple correction formula to the measured pulse height distributions. The comparison between former theoretical or experimental studies and our results showed that there was no evidence of additional performance degradation within the tested energy range in terms of the linearity and the energy resolution compared to conventional non-avalanching silicon detectors. Thanks to the low noise level (equivalent to 0.9 keV in silicon) at the room temperature even for a large detection area (15 mm $^2$ ), APDs would be potentially used for detection of low-energy ions in various environments such as space plasma physics, particle physics, and many industrial applications.

Description: Nonuniformity in charge transport properties is a limiting factor in energy resolution of radiation detectors. In this paper, we investigate variations in the low temperature ambipolar diffusion length and the mobility-lifetime $(mu tau)$ product in bulk doped TlBr using cathodoluminescence (CL) and transport imaging. One TlBr crystal was doped with sodium (Na), aluminum (Al), and silver (Ag). A second TlBr crystal was doped with copper (Cu), iron (Fe), and zinc (Zn). We report the first low temperature high resolution CL spectroscopy and mapping in bulk doped TlBr, showing spatial variation in recombination luminescence on a scale of $sim 10~mu{rm m}$ . Transport imaging is applied to quantify these variations in TlBr at 5 K. Ambipolar diffusion lengths and $mu tau$ products, dominated by the transport of holes, are mapped across a $40~mu{rm m}$ segment of TlBr at a resolution of $2~mu{rm m}$ . Ambipolar diffusion lengths are found to vary between $4.6~mu{rm m}$ and $11.2~mu{rm m}$ , on a spatial scale comparable to the variation observed in the CL map.

Description: A very low power 16-channel ASIC has been designed and fabricated in a standard 0.35 $mu{hbox{m}}$ CMOS technology. It is to be used as the front-end electronics of the micro-channel plates (MCPs) based detector of a 3D space plasma analyzer. Each channel includes a charge sensitive amplifier (CSA) and a discriminator. With a CSA conversion gain of 0.5 mV/fC, the ASIC is able to detect charges emitted by the MCPs over a wide dynamic range of 10 fC to 3.5 pC. The CSA pulse-pair-resolution (PPR) is 170 ns, and the maximum counting rate frequency is 7.5 MHz for input charges limited to 100 fC and 4.6 MHz for full scale inputs. The CSA input devices are optimized for a detector capacitance varying in the range of 2–12 pF. The measured input equivalent noise charge $({hbox{ENC}}_{rm in})$ is 1.3 fC $+$ 0.1 fC/pF rms. These features have been obtained with an unprecedented low power consumption of only 0.64 mW per channel. Experimental tests under the extended temperature range of $-{hbox{40}}~^{circ}{hbox{C}}$ to 85 $~^{circ}{hbox{C}}$ have shown no significant performance variations.

Description: While polycrystalline ceramic of Ce $^{+ 3}$ doped lutetium oxyorthosilicate (LSO) has demonstrated scintillation characteristics equivalent to those of single crystal material, it lacks in optical quality. It is projected that if their grain size could be reduced to the nanometer range they would be smaller than the wavelength of light thereby minimizing scattering and substantially improving optical quality. In this investigation ceramic LSO:Ce that is much more transparent than would be expected from a highly anisotropic material, has been successfully produced by hot pressing at 75 MPa in a graphite die and furnace. The conditions necessary for powder processing and densification were optimized so as to produce dense LSO:Ce ceramic discs with an average grain size of 700 nm. Appreciable improvement in optical properties was observed, with decay and emission levels comparable with LSO single crystals, the light output was some 20% below that of single crystal. The degradation of light output in the nanoceramic is attributed to the formation of quenching centers associated with the loss of oxygen during densification, to which such nanomaterials are highly susceptible.

Description: Thin-film-on-ASIC (TFA) detectors are monolithic pixel devices that consist of amorphous silicon detecting diodes directly deposited on readout electronics.

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

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: This form is intended for original material submitted to the IEEE and must accompany any such material in order to be published by the IEEE.

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Description: Provides a listing of current society officers.

Description: The quest for choosing the suitable detector for a specific homeland security application that takes an advantage of the neutron activation analysis technique prompted us to investigate properties of three 3 '' × 3 '' cylindrical scintillation detectors. The emphasis was put on the detectors' properties in the multi-MeV energy region and their response to the neutron radiation. In this work we compare the energy resolution, efficiency and timing properties of BGO, LaBr 3 and NaI(Tl) scintillation detectors coupled to Photonis spectrometric photomultiplier tubes.

Description: In recent years, progress in processing and crystal growth methods have led to a significant increase in the mobility-lifetime product of electrons in thallium bromide (TlBr). This has enabled single carrier collection devices with thickness greater than 1-cm to be fabricated. In this paper we report on our latest results from pixellated devices with depth correction as well as our initial results with Frisch collar devices. After applying depth corrections, energy resolution of approximately 2% (FWHM at 662 keV) was obtained from a 13-mm thick TlBr array operated at -18°C and under continuous bias and irradiation for more than one month. Energy resolution of 2.4% was obtained at room temperature with an 8.4-mm thick TlBr Frisch collar device.

Description: TID test results of CMOS Flash-based FPGAs in gamma-rays are presented. The use of realistic low dose-rates and oriented bias-conditions are shown to extend the FPGA TID tolerance. Implications to qualification methods and to most of the new CMOS technologies are noted.

Description: This work is intended to provide a set of guidelines for the design of digital-to-analog converters enabling the reduction of threshold dispersion in multichannel readout circuits for radiation detectors. The design criteria are first established through a theoretical approach and then confirmed by means of a simulation tool based on Monte Carlo methods. This latter tool provides a fast and flexible way to predict the performance of a DAC for threshold correction, also accounting for possible non-idealities, such as differential and integral non linearities and gain and offset errors. The proposed guidelines have been validated through simulations on front-end circuits for a real application, the silicon vertex tracker for the SuperB Factory, and through comparison with data available in the literature.

Description: An increasing number of civil nuclear reactors world wide are approaching, and have in many cases exceeded, their original design lives. In order to satisfy regulatory requirements and ensure that the reactors are safe to operate, whilst maximizing availability and ensuring economic viability, the volume of installed condition monitoring has increased significantly in recent years. Due to the age of many stations however, there is often the lack of a modern, integrated IT infrastructure with many, often overlapping, data sources of varying measurement types and sample rates. This paper describes a method for the distributed condition monitoring of nuclear reactors using intelligent software agents, which by means of a common ontology can autonomously collect and analyze data from multiple locations. The use of data and information fusion to derive more detailed condition monitoring results is shown to be a task well suited to agent based condition monitoring and a prototype system designed along these principles is described. Case studies are presented of the application of the prototype system to condition monitoring analysis of real data sets from nuclear reactors in the UK.

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 herein. Affiliates pay a special fee and have all Society privileges except that of holding elective office. Affiliates receive the IEEE Transactions on Plasma Science.

Description: An ultrasonic under-sodium scanner has been developed for deployment in Prototype Fast Breeder Reactor (PFBR) which is in advanced stage of construction at Kalpakkam, India. Its purpose is to scan the above-core plenum for detection, if any, of displacement of sub-assemblies. During its burn-up in the reactor, the head of a Fuel Sub-Assembly (FSA) may undergo a lateral shift from its original position (called `bowing') due to the fast neutron induced damage on its structural material. A simple scanning technique has been developed for measuring the extent of bowing in-situ. This paper describes a PC-controlled mock-up of the scanner used to implement the scanning technique and the results obtained of scanning a mock-up FSA head under water. The details of the liquid-sodium proof transducer developed for use in the PFBR scanner and its performance are also discussed.

Description: Silicon photomultipliers (SiPMs) are expected to replace photomultiplier tubes (PMTs) in several applications that require scintillation detectors with excellent timing resolution, such as time-of-flight positron emission tomography (TOF-PET). However, the theory about the timing resolution of SiPM-based detectors is not yet fully understood. Here we propose a comprehensive statistical model to predict the timing resolution of SiPM-based scintillation detectors. It incorporates the relevant SiPM-related parameters (viz. the single cell electronic response, the single cell gain, the charge carrier transit time spread, and crosstalk) as well as the scintillation pulse rise and decay times, light yield, and energy resolution. It is shown that the proposed model reduces to the well-established Hyman model for timing with PMTs if the number of primary triggers (photoelectrons in case of a PMT) is Poisson distributed and crosstalk and electronic noise are negligible. The model predictions are validated by measurements of the coincidence resolving times (CRT) for 511 keV photons of two identical detectors as a function of SiPM bias voltage, for two different kinds of scintillators, namely LYSO:Ce and LaBr 3 :5%Ce. CRTs as low as 138 ps ± 2 ps FWHM for LYSO:Ce and 95 ps ± 3 ps FWHM for LaBr 3 :5%Ce were obtained, demonstrating the outstanding timing potential of SiPM-based scintillation detectors. These values were found to be in good agreement with the predicted CRTs of 140 ps FWHM and 95 ps FWHM, respectively. Utilizing the proposed model, it can be shown that the CRTs obtained in our experiments are mainly limited by photon statistics while crosstalk, electronic noise and signal bandwidth have relatively little influence.

Description: With decreasing circuit lithography dimensions and increasing memory densities, an SEU may affect multiple adjacent memory cells. This paper presents an SEU hardened memory using error correction code that can correct single errors, double-adjacent errors, triple-adjacent errors and double-almost-adjacent errors. The proposed memory introduces small area, power and delay overheads.

Description: Non-proportionality of light yield and energy resolution of Compton electrons in three scintillators (LaBr 3 :Ce, LYSO:Ce and CsI:Tl) were studied in a wide energy range from 10 keV up to 1 MeV. The experimental setup was comprised of a High Purity Germanium detector and tested scintillators coupled to a photomultiplier. Probing the non-proportionality and energy resolution curves at different energies was obtained by changing the position of various radioactive sources with respect to both detectors. The distance between both detectors and source was kept small to make use of Wide Angle Compton Coincidence (WACC) technique, which allowed us to scan large range of scattering angles simultaneously and obtain relatively high coincidence rate of 100 cps using weak sources of about 10 μCi activity. The results are compared with those obtained by direct irradiation of the tested scintillators with gamma-ray sources and fitting the full-energy peaks.

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

Description: Silicon diodes with large aspect ratio trenched microstructures, backfilled with 6 LiF, show a dramatic increase in thermal neutron detection efficiency beyond that of conventional thin-film coated planar devices. Described in this work are advancements in the technology using detector stacking methods to increase thermal neutron detection efficiency, along with the current process to backfill 6 LiF into the silicon microstructures. The highest detection efficiency realized thus far is over 42% intrinsic thermal neutron detection efficiency by device-stacking methods. The detectors operate as conformally diffused pn junction diodes each having 1 cm 2 area. Two individual devices were mounted back-to-back with counting electronics coupling the detectors together into a single dual-detector device. The solid-state silicon device was operated at 3 V and utilized simple signal amplification and counting electronic components that have been adjusted from previous work for slow charge integration time. The intrinsic detection efficiency for normal-incident 0.0253 eV neutrons was found by calibrating against a 3 He proportional counter.

Description: Colloidal semiconductor nanocrystals exhibit physical properties that are characteristic of intermediate size scales between molecular states and solid state materials, and are often called quantum dots. Solid state semiconductor materials have been used extensively as scintillation detectors for ionizing radiation. We describe the use of semiconductor quantum dot-organic polymer composites for use as scintillation detectors and report the use of quantum dot-polymer composite thin films for X-ray imaging.

Description: Two 20 mm × 20 mm × 15 mm pixelated CZT detectors made by eV-Products were characterized using the new H3D Application Specific Integrated Circuits (ASIC) readout system developed by the Instrumentation Division at Brookhaven National Laboratory. The ASIC is capable of reading out energy and timing signals from 121 anode pixels and the planar cathode electrode of one CZT detector simultaneously. The system has a measured electronic noise of ~2.2 keV FWHM with a dynamic range from 20 keV to 3.0 MeV. The two detectors achieved energy resolution of 0.48% FWHM and 0.60% FWHM, respectively, at 662 keV for single-pixel events from the entire 6.0 cm 3 detection volume at room temperature with an un-collimated 137 Cs source. The average (μτ) e of both detectors were measured to be 〉; 10 -2 cm 2 /V. The detection efficiency of the two detectors was evaluated at several different energies up to 1.3 MeV by comparing with simulated data. It was found that the total counts agree well between the measured data and the simulated data over the studied energy range. However, the measured photopeak counts were 10-15% lower than simulated photopeak counts at high gamma-ray energies. The analysis shows that the loss of photopeak efficiency is likely due to the charge loss from peripheral pixels to the boundary of detectors.

Description: This paper presents an SEU hardened latch that can mitigate SEU based on an error detection circuit and a multiplexer. During the hold phase, an SEU on an internal node may upset the logic state of the latch. But the error detection circuit can detect this fault and generate fault indication signals via precharge and discharge operations. The fault indication signals control a multiplexer to select a correct output. Therefore, each latch has some error detection and correction capability.

Description: The scanning of cargo for radiological and nuclear material is vital in detecting the illicit trafficking of such materials. The deployment of technologies such as Radiation Portal Monitors (RPMs) has enabled screening for the presence of gamma and neutron emitting radionuclides. Although the development of radionuclide detection algorithms is vital to the development of RPMs, only a small amount of the work exists in the published literature. This paper describes the development of an anomalous signature detection algorithm based on Principal Component Analysis (PCA). PCA involves the eigen decomposition of the correlation matrix of a training data set. The distance of an unknown observed spectrum from Naturally Occurring Radioactive Materials (NORM), in a 14 dimensional space, was used to assess the algorithm performance. The PCA algorithm showed an excellent 'anomaly detection' performance for a number of threat sources including Special Nuclear Materials (SNM's). The PCA algorithm has also demonstrated an improved performance over that of a commercially available peak search algorithm. The discrimination of the SNM's sources, from the NORM, consistently improved with increased counts, which is not always true for peak search based algorithms. The algorithm also performed well in count starved spectra, which is of relevance to border security applications of RPMs.

Description: Response measurements of a Bonner sphere spectrometer (BSS) were performed for high-energy neutrons up to 400 MeV in quasi-monoenergetic neutron fields at the Research Center for Nuclear Physics (RCNP), Osaka University. The quasi-monoenergetic neutron field was generated by a 7 Li(p,n) reaction with the resulting spectra consisting of a monoenergetic high-energy peak followed by an unwanted continuum tail down to the low-energy region. Two-angle differential measurements for a variety of Bonner spheres were performed to obtain monoenergetic responses by subtracting the tail contributions. Discussions were made on data analysis for tail subtraction. While each Bonner sphere had a different energy response, good agreements were seen in the responses between the MCNPX calculations and the measurements with a suitable subtraction. Response calculations were also made for the whole spectra obtained by unfolding the measured BSS data, with results that reproduce well the measured responses.

Description: Novel fabrication methods for cost-effective and large-volume production of important lanthanide halide scintillators are currently being explored.

Description: Positron emission tomography (PET) detectors based on continuous scintillation crystals can achieve very good performance and have a number of practical advantages compared to detectors based on a pixelated array of crystals. Our goal is to develop a thick continuous detector with high energy and spatial resolution, along with high $gamma$ -photon capture efficiency. We examine the performance of two crystal blocks: a 46 $,times,$ 46 $,times,$ 14 mm $^{3}$ and a 48 $,times,$ 48 $,times,$ 25 mm $^{3}$ block of LYSO (Lutetium Yttrium Orthosilicate). Using Maximum Likelihood (ML) positioning based upon the light response function (LRF) in the 14 mm thick crystal, we measure a spatial resolution of 3 mm in the central region of the crystal with degradation near the edges due to reflections off the crystal sides. We also show that we can match the spatial resolution achieved using a 14 mm thick crystal by using a 25 mm thick crystal with slots cut into the gamma entrance surface to narrow the LRF. We also find that we can improve the spatial resolution performance near the detector edges by reducing the reflectivity of the crystal sides, albeit with some loss in energy resolution.

Description: We demonstrate a new scintillator material that has a one-dimensional eutectic structure and optical light-guiding properties. Our light propagation calculations predicted that a structure where high refractive index luminescence cylinders are embedded in a matrix should show effective light-guiding properties. An inverse structure where a high refractive index luminescence matrix contains low refractive index cylinders was also predicted to possess light-guiding properties. A CsI—NaCl:Tl eutectic phase, which contained NaCl cylinders in a CsI matrix, was grown by a one-dimensional solidification method. This material showed high spatial resolution because of the difference in the refractive indices of NaCl and CsI.

Description: We are proposing a novel design for a module with depth of interaction (DOI) capability for gamma rays by measuring the pulse-height ratio of double-sided Multi-Pixel Photon Counters (MPPCs) coupled at both ends of a scintillation crystal block. Thanks to newly developed monolithic MPPC arrays consisting of 4 $times$ 4 channels with a three-side buttable package, the module is very thin and compact, thereby enabling less dead space between each module when arranged into a fully designed gantry. To demonstrate our concept of a DOI measuring technique, we first made a 1-D crystal array consisting of five Ce-doped ${rm Gd}_{3}{rm Al}_{2}{rm Ga}_{3}{rm O}_{12}$ (Ce:GAGG) cubic crystals measuring $3times 3times 3 {rm mm}^{3}$ in size, separated by a layer of air approximately 10 $mu{rm m}$ -thick. When the light signals output from both ends are read with the $3times 3 {rm mm}^{2}$ MPPCs, the position of each crystal is clearly distinguished. The same measurements were also made using Ce-doped $({rm Lu},{rm Y})_{2}({rm SiO}_{4}){rm O}$ (Ce:LYSO), achieving a similarly good separation. We then fabricated thin Ce:GAGG 2-D crystal arrays consisting of two types: [A] 4 $times$ 4 matrix of $3times 3times 3 {rm mm}^{3}$ pixels, and [B] 10 $times$ 10 matrix of $0.8times 0.8times 5 {rm mm}^{3}$ pixe- s, with each pixel divided by a ${rm BaSO}_{4}$ reflector 0.2 mm-thick. Then four arrays are laid on top of each other facing the DOI direction through a layer of air 10 $mu{rm m}$ -thick. We demonstrated that the 3-D position of each Ce:GAGG pixel is clearly distinguished in both the 2-D and DOI directions for type A and B when illuminated by 662 keV gamma rays. Average energy resolutions of 9.8 $pm$ 0.8% and 11.8 $pm$ 1.3% were obtained for types A and B, respectively. These results suggest that our proposed method is simple and offers promise in achieving both excellent spatial and energy resolutions for future medical imaging, particularly in positron emission tomography (PET).

Description: We developed SPECT imaging capability on a LabPET animal scanner to provide an integrated PET/SPECT dual-modality imaging system. The add-on SPECT sub-system was enabled by 1) mechanically integrating a multiple-pinhole collimator in the PET detector ring, and 2) configuring the detectors to acquire singles events in the 120–160 keV range. We report on the design parameters, data acquisition protocols and initial performance assessment of this cost-effective SPECT imaging solution. Phantom and animal images demonstrating the relevance of the system for various imaging tasks in preclinical research are presented.

Description: Collimation can improve both the spatial resolution and sampling properties compared to the same scanner without collimation. Spatial resolution improves because each original crystal can be conceptually split into two (i.e., doubling the number of in-plane crystals) by masking half the crystal with a high-density attenuator (e.g., tungsten); this reduces coincidence efficiency by 4 $times$ since both crystals comprising the line of response (LOR) are masked, but yields 4 $times$ as many resolution-enhanced (RE) LORs. All the new RE LORs can be measured by scanning with the collimator in different configurations.

Description: Images taken with time-of-flight (TOF) positron emission tomography (PET) scanners are of improved quality compared to equivalent non-TOF images. This improvement is dependent on the scanner time resolution. The present generation of commercial TOF scanners has a time resolution in the range of 500–600 ps full width half maximum. In this work we investigate how the image characteristics will improve for future generations of TOF PET. We performed a Geant4 simulation of a 30-cm uniform cylinder containing hot spheres, with time resolution ranging from 600 to 200 ps. Data were reconstructed using TOF filtered back projection (FBP) and TOF ordered subsets expectation maximization (OSEM), with nonTOF reconstruction as a reference. Images were compared in terms of contrast recovery and variance in the image. The TOF gain was evaluated for both reconstruction methods. The TOF gain was also evaluated vs. counts in the scan, in order to understand the behavior of such gain at very low statistics. Using TOF FBP, it was shown that the TOF gain can be used as a sensitivity amplifier, reducing (according to the expected TOF gain) the number of counts necessary to produce an image of the same characteristics. Some limitations in the TOF gain were observed at very low counts, particularly if using iterative methods.

Description: We investigate the capability to perform K-edge imaging with the newly developed micro-CT PIXSCAN based on the XPAD3 hybrid pixel detector. The XPAD3 detector surface of $8~{rm cm} times 11~{rm cm}$ makes it possible to perform whole body mouse imaging. We present a proof of principle of K-edge imaging of mouse-size phantoms filled with Silver and Iodine solutions. Results are compared with standard X-ray absorption tomography for several solution densities.

Description: We are currently investigating the feasibility of using highly pixelated Cadmium Zinc Telluride (CdZnTe) detectors for sub-500 $mu$ m resolution PET imaging applications. A 20 mm $,times,$ 20 mm $,times,$ 5 mm CdZnTe substrate was fabricated with 350 $mu$ m pitch pixels (250 $mu$ m anode pixels with 100 $mu$ m gap) and coplanar cathode. Charge sharing among the pixels of a 350 $mu$ m pitch detector was studied using collimated 122 keV and 511 keV gamma ray sources. For a 350 $mu$ m pitch CdZnTe detector, scatter plots of the charge signal of two neighboring pixels clearly show more charge sharing when the collimated beam hits the gap between adjacent pixels. Using collimated Co-57 and Ge-68 sources, we measured the count profiles and estimated the intrinsic spatial resolution of 350 $mu$ m pitch detector biased at ${-}1000$ V. Depth of interaction was analyzed based on two methods, i.e., cathode/anode ratio and electron drift time, in both 122 keV and 511 keV measurements. For single-pixel photopeak events, a linear correlation between cathode/anode ratio and electron drift time was shown, which would be useful for estimating the DOI information and preserving image resolution in CdZnTe PET imaging applications.

Description: This article describes a compact single-photon emission computed tomography (SPECT) system that consists of a high-resolution detector combined with a lofthole collimator. The detector is based on a NaI(Tl) scintillator, a position sensitive photomultiplier (PSPMT), dedicated read-out electronics that digitize all PSPMT anodes and finally, a maximum likelihood algorithm for position estimation. The collimator has a new pinhole geometry, called the lofthole. Our choice of magnification (1.06 for the mouse setup, 0.63 for the rat setup) results in a small system with a footprint of 45 cm $,times,$ 25 cm.

Description: The redundancy in 3D time-of-flight (TOF) PET data can be exploited to reduce data storage or to estimate unmeasured data samples caused by defective or missing detectors. Mathematically, redundancy is expressed by consistency conditions which can be expressed either in terms of the 3D Fourier transform of the data or as a pair of partial differential equations (PDE). The benefit of the latter is that the PDEs are local and therefore can be applied even if some data samples are missing.

Description: While the performance of most current commercially available PET scanners is sufficient for many standard clinical applications, some specific tasks likely require specialized imaging systems. The goal of this project is to explore the capabilities and limitations of a small, high-resolution prototype system for obtaining PET images. The scanner consists of a tandem of detectors. One is a small detector consisting of a 20 $,times,$ 20 array of $0.7times 0.7times 3~{hbox {mm}}^{3}$ (pitch 0.8 mm) LYSO elements. The scintillator array is coupled to an array of silicon photomultipliers. The second detector is a 96 $,times,$ 72 array of $2times 2times 15~{hbox {mm}}^{3}~({rm pitch}=2.1~{hbox {mm}})$ LYSO elements coupled to PSPMTs. Separation between the two devices is 180 mm. The detectors are operated in coincidence with each other. Image reconstruction is performed using a limited angle, Maximum Likelihood Expectation Maximization (MLEM) algorithm. Evaluation of the device included measurements of spatial resolution and detection sensitivity as a function of distance. The transaxial radial and tangential spatial resolution of the system ranged from 0.6 mm to 0.9 mm FWHM; axial resolution ranged from 2.7 mm to 4.6 mm FWHM. Detection sensitivity ranged from 0.05 to 0.28%. Spatial resolution and field-of-view vary as a function of distance from the small detector. The tandem detector insert permitted differentiation of the smallest (1 mm diameter) rods in a mini-hot rod phantom. The results indicate that a tandem PET imaging scheme can be potentially employed in applications where high-resolution images over a small region are required.

Description: Positron Emission Tomography (PET) is an imaging method affected by artifacts caused by patient motion. PET-MR simultaneous acquisition may provide the means to correct for the effects of motion. This study investigates the creation of a deformable PVA cryogel phantom for motion correction purposes in PET-MR. This phantom has to contain the appropriate concentration of PVA and a sufficient amount of radioactive tracer along with gadolinium contrast agent. The effect of modifying the standard PVA cryogel process were assessed by measuring differences in the Young's modulus and also the diffusion of radiotracer inside the phantom. The alteration of the freeze-thaw cycle decreased the Young's modulus up to 50% by comparison with the standard MRI cryogel phantom. The diffusion speed on the other hand was found to be at 2 mm h $^{-1}$ inside a 10% p.w. cryogel. The results are demonstrated with a simultaneous PET-MR experiment. The new approach of cryogel preparation provides the opportunity to create a PET and MR visible phantom with structural complexity and customized shape, which is capable of reproducible deformations when reproducible pressure is applied. The methodology to build the phantom can be used in other simultaneous or sequential imaging modalities such as SPECT and ultrasound.

Description: Most of the regularized iterative reconstruction schemes employed in emission tomography (such as penalized maximum-likelihood, PML) usually require the adjustment of a scalar parameter $beta$ that determines the strength of the a priori information regarding the studied object. Empirical selection of $beta$ remains hazardous since its optimal value depends on the morphological structure of the reconstructed image and the data signal to noise ratio (SNR), which explains partly the scarce utilization of penalized reconstruction in clinical routine. In this paper, we derive a simple optimization criterion for $beta$ that relies on a statistical description of the noise propagation when iteratively updating the image estimate and on a surrogate algebraic formulation holding for both PML and expectation-maximization-smooth (EMS) iterative reconstruction. When incorporated into each iteration step, the statistic-algebraic tuning optimization (SATO) yields two new optimized regularized iterative methods: SATO-PML and SATO-EMS. These methods are compared with classical MLEM reconstruction followed by optimal Gaussian post-filtering (ML-opt) through Monte-Carlo experiments involving the Hoffman brain phantom and the Shepp-Logan phantom. It is shown that, whatever the studied object and the count rate, SATO-PML and SATO-EMS are convergent in terms of $beta$ and produce images with bias, variance and contrast properties that are at least as good as those of the ML-opt images. The two proposed algorithms are also evaluated using realistic PET data from a Hoffman phantom produced using the GATE platform in order to demonstrate the feasibility of our SATO scheme with actual data.

Description: Currently, radiotherapy with electrons and photons beams is the most common approach in health care facilities; it allows widespread use of technology. Only a fast and accurate verification of the dose characteristics of the beams provides a safe and effective use of the methodology. We have designed, built and tested a new instrument based on a layer of square scintillating fibers of 0.5 mm thickness that can run a scan of the beam. The system provides the dosage profiles, related to a plane orthogonal to the beam axis at a fixed depth. The device was tested with a photon beam of 6 MV delivered by a linear accelerator Varian Clinac DHX 2100. The data collected were processed for the tomographic reconstruction of the dose by means of the FBP (filtered back projection) algorithm with different filters. An iterative reconstruction algorithm was also tested. In this paper, the results are presented and suggestions for future developments are made.

Description: We describe a GPU-accelerated framework that efficiently models spatially (shift) variant system response kernels and performs forward- and back-projection operations with these kernels for the DIRECT (Direct Image Reconstruction for TOF) iterative reconstruction approach. Inherent challenges arise from the poor memory cache performance at non-axis aligned TOF directions. Focusing on the GPU memory access patterns, we utilize different kinds of GPU memory according to these patterns in order to maximize the memory cache performance. We also exploit the GPU instruction-level parallelism to efficiently hide long latencies from the memory operations. Our experiments indicate that our GPU implementation of the projection operators has slightly faster or approximately comparable time performance than FFT-based approaches using state-of-the-art FFTW routines. However, most importantly, our GPU framework can also efficiently handle any generic system response kernels, such as spatially symmetric and shift-variant as well as spatially asymmetric and shift-variant, both of which an FFT-based approach cannot cope with.

Description: The spatial resolution in positron emission tomography (PET) can be improved by the addition of depth-of-interaction (DOI) information. This can be achieved by using the phoswich approach in which depth identification relies on differences in scintillation decay time and pulse shape discrimination techniques. In this paper we have looked at a special phoswich combination LuAP/LSO or LuYAP/LSO. This combination of scintillators is especially interesting since LuAP and LuYAP have emission in the excitation band of LSO, which may have an impact on the timing resolution of the detector. As will be shown in this paper, the phoswich concept based on these two scintillators can be utilized, however, with some limitations. This paper is an extension of our previous phoswich investigation .

Description: Maximum Likelihood (ML) reconstruction estimators are non biased and achieve the lowest variance, called the Cramer-Rao lower bound (CRLB), in the asymptotic regime, which in positron emission tomography (PET) or in single photon emission tomography (SPECT) corresponds to measuring an infinite number of counts. At finite number of counts or iterations, practical reconstruction algorithms are however biased, and nothing guarantees that the minimum variance expressed by the CRLB is achieved. We study the two dimensional Ordered Subsets Expectation Maximization (2D OSEM) algorithm with a finite number of counts and iterations, and investigate the question: given its bias, does this algorithm achieve the minimum variance predicted by the biased Cramer-Rao lower bound?

Description: Stationary small-animal SPECT systems are being developed for rapid dynamic imaging from limited angular views. This work quantified, through simulations, the performance of Maximum Likelihood Expectation Maximization (MLEM) for reconstructing a time-activity curve (TAC) with uptake duration of a few seconds from a stationary, three-camera multi-pinhole SPECT system. The study also quantified the benefits of a heuristic method of initializing the reconstruction with a prior image reconstructed from a conventional number of views, for example from data acquired during the late-study portion of the dynamic TAC. We refer to MLEM reconstruction initialized by a prior-image initial guess (IG) as ${rm MLEM}_{ig}$ . The effect of the prior-image initial guess on the depiction of contrast between two regions of a static phantom was quantified over a range of angular sampling schemes. A TAC was modeled from the experimentally measured uptake of $^{99m}{rm Tc}$ -hexamethylpropyleneamine oxime (HMPAO) in the rat lung. The resulting time series of simulated images was quantitatively analyzed with respect to the accuracy of the estimated exponential washin and washout parameters. In both static and dynamic phantom studies, the prior-image initial guess improved the spatial depiction of the phantom, for example improved definition of the cylinder boundaries and more accurate quantification of relative contrast between cylinders. For example in the dynamic study, there was ${sim}50%$ error in relative contrast for MLEM reconstructions compared to ${sim}{25}$ -30% error for ${rm MLEM}_{ig}$ . In the static phantom study, the benefits of the initial gues- decreased as the number of views increased. The prior-image initial guess introduced an additive offset in the reconstructed dynamic images, likely due to biases introduced by the prior image. MLEM initialized with a uniform initial guess yielded images that faithfully reproduced the time dependence of the simulated TAC; there were no statistically significant differences in the mean exponential washin/washout parameters estimated from MLEM reconstructions compared to the true values. Washout parameters estimated from ${rm MLEM}_{ig}$ reconstructions did not differ significantly from the true values, however the estimated washin parameter differed significantly from the true value in some cases. Overall, MLEM reconstruction from few views and a uniform initial guess accurately quantified the time dependance of the TAC while introducing errors in the spatial depiction of the object. Initializing the reconstruction with a late-study initial guess improved spatial accuracy while decreasing temporal accuracy in some cases.