Showing papers in "IEEE Transactions on Nuclear Science in 2006"

Geant4 developments and applications

Abstract: Geant4 is a software toolkit for the simulation of the passage of particles through matter. It is used by a large number of experiments and projects in a variety of application domains, including high energy physics, astrophysics and space science, medical physics and radiation protection. Its functionality and modeling capabilities continue to be extended, while its performance is enhanced. An overview of recent developments in diverse areas of the toolkit is presented. These include performance optimization for complex setups; improvements for the propagation in fields; new options for event biasing; and additions and improvements in geometry, physics processes and interactive capabilities

Total-Ionizing-Dose Effects in Modern CMOS Technologies

Abstract: This review paper discusses several key issues associated with deep submicron CMOS devices as well as advanced semiconductor materials in ionizing radiation environments. There are, as outlined in the ITRS roadmap, numerous challenges ahead for commercial industry in its effort to track Moore's Law down to the 45 nm node and beyond. While many of the classical threats posed by ionizing radiation exposure have diminished by aggressive semiconductor scaling, the question remains whether there may be unknown, potentially worse threats lurking in the deep submicron regime. This manuscript provides a basic overview of some of the materials, devices, and designs that are being explored or, in some cases, used today. An overview of radiation threats and how radiation effects can be characterized is also presented. Last, the paper provides a detailed discussion of what we know now about how modern devices and materials respond to radiation and how we may assess, through the use of advanced analysis and modeling techniques, the relative hardness of future technologies

Charge Collection and Charge Sharing in a 130 nm CMOS Technology

Abstract: Charge sharing between adjacent devices can lead to increased Single Event Upset (SEU) vulnerability. Key parameters affecting charge sharing are examined, and relative collected charge at the hit node and adjacent nodes are quantified. Results show that for a twin-well CMOS process, PMOS charge sharing can be effectively mitigated with the use of contacted guard-ring, whereas a combination of contacted guard-ring, nodal separation, and interdigitation is required to mitigate the NMOS charge sharing effect for the technology studied

A high-resolution time-to-digital converter implemented in field-programmable-gate-arrays

Abstract: A high-resolution time-to-digital converter (TDC) implemented in a general purpose field-programmable-gate-array (FPGA) is presented. Dedicated carry lines of an FPGA are used as delay cells to perform time interpolation within the system clock period and to realize the fine time measurement. Two Gray-code counters, working on in-phase and out-of-phase system clocks respectively, are designed to get the stable value of the coarse time measurement. The fine time code and the coarse time counter value, along with the channel identifier, are then written into a first-in first-out (FIFO) buffer. Tests have been done to verify the performance of the TDC. The resolution after calibration can reach 50 ps

Statistical Analysis of the Charge Collected in SOI and Bulk Devices Under Heavy lon and Proton Irradiation—Implications for Digital SETs

Abstract: The statistical transient response of floating body SOI and bulk devices is measured under proton and heavy ion irradiation. The influence of the device architecture is analyzed in detail for several generations of technologies, from 0.25 mum to 70nm. The effects of the measured transients on SET sensitivity are investigated. The amount of collected charge and the shape of the transient currents are shown to have a significant impact on the temporal width of propagating transients. Finally, based on our measured data, the threshold LET and the critical transient width for unattenuated propagation are calculated for both bulk and floating body SOI as a function of technology scaling. We show that the threshold LETs and the critical transient widths for bulk and floating body SOI devices are similar. Body ties can be used to harden SOI ICs to digital SET. However, the primary advantage of SOI technologies, even with a floating body design, mostly lies in shorter transients, at a given ion LET, for SOI technologies than for bulk technologies

Geometry Description Markup Language for Physics Simulation and Analysis Applications

Abstract: The Geometry Description Markup Language (GDML) is a specialized XML-based language designed as an application-independent persistent format for describing the geometries of detectors associated with physics measurements. It serves to implement "geometry trees" which correspond to the hierarchy of volumes a detector geometry can be composed of, and to allow to identify the position of individual solids, as well as to describe the materials they are made of. Being pure XML, GDML can be universally used, and in particular it can be considered as the format for interchanging geometries among different applications. In this paper we will present the current status of the development of GDML. After having discussed the contents of the latest GDML schema, which is the basic definition of the format, we will concentrate on the GDML processors. We will present the latest implementation of the GDML "writers" as well as "readers" for either Geant4 , or ROOT ,

Digital Single Event Transient Trends With Technology Node Scaling

Abstract: We have measured the single-event-transient (SET) width as a function of cross-section over three CMOS bulk/epitaxial technology nodes (0.25, 0.18 and 0.13 mum) using an identically scaled programmable-delay temporal-latch technique. Both the maximum width of the SET pulse and the cross-section are shown to depend primarily on the supply voltage, with a substantial increase in transient width and cross-section with lower operating potentials

Design and evaluation of the clear-PEM scanner for positron emission mammography

Abstract: The design and evaluation of the imaging system Clear-PEM for positron emission mammography, under development by the PEM Consortium within the framework of the Crystal Clear Collaboration at CERN, is presented. The proposed apparatus is based on fast, segmented, high atomic number radiation sensors with depth-of-interaction measurement capabilities, and state-of-the-art data acquisition techniques. The camera consists of two compact and planar detector heads with dimensions 16.5/spl times/14.5 cm/sup 2/ for breast and axilla imaging. Low-noise integrated electronics provide signal amplification and analog multiplexing based on a new data-driven architecture. The coincidence trigger and data acquisition architecture makes extensive use of pipeline processing structures and multi-event memories for high efficiency up to a data acquisition rate of one million events/s. Experimental validation of the detection techniques, namely the basic properties of the radiation sensors and the ability to measure the depth-of-interaction of the incoming photons, are presented. System performance in terms of detection sensitivity, count-rates and reconstructed image spatial resolution were also evaluated by means of a detailed Monte Carlo simulation and an iterative image reconstruction algorithm.

TUKAN-an 8K pulse height analyzer and multi-channel scaler with a PCI or a USB interface

Abstract: In this paper we present two types of 8K-channel analyzers designed for spectroscopy and intensity versus time measurements. The first type (Tukan-8K-PCI) incorporates a PCI interface and is designed to be plugged into a PCI slot of a normal PC. The second type (Tukan-8K-USB) incorporates a USB interface. It is mounted in a separate screened box and can be powered either directly from the USB port or from an external dc source (wall adapter or battery). Each type of device may operate in either of two independent operational modes: Multi Channel Analysis (MCA) and Multi-Channel Scaling (MCS). The most crucial component for the MCA mode-the Peak Detect and Hold circuit-is featuring a novel architecture based on a diamond transistor. Its analog stage can accept analog pulses with rise times as short as 100 ns and has a differential linearity below 1% with sliding scale averaging over the full scale. The functionality includes automatic stop on a programmable count in the Region-Of-Interest (ROI) and on preset live- or real time. The MCS mode works at medium counting rates of up to 8 MHz. The dwell time, the number of channels and single or multi-sweep mode may be preset. Each of these parameters can also be controlled externally via four user configurable logical I/O lines. A single Altera FLEX 10KE30 FPGA provides all control functions and incorporates PCI interface. The USB interface is based on FTDI FIFO controller. Advanced and user-friendly software has been developed for the analyzer

SEE and TID Characterization of an Advanced Commercial 2Gbit NAND Flash Nonvolatile Memory

Abstract: An advanced commercial 2Gbit NAND flash memory (90 nm technology, one bit/cell) has been characterized for TID and heavy ion SEE Results are qualitatively similar to previous flash results in most respects, but we also detected a new dynamic failure mode

Model-based registration of X-ray mammograms and MR images of the female breast

Abstract: We present a new approach for automatic registration of X-ray mammograms and MR images. Multimodal breast cancer diagnosis is supported by automatic localization of small lesions, which are only visible in the mammograms or in the MR image. To cope with the huge deformation of the breast during mammography, a finite element model of the deformable behavior of the breast is applied during the registration. An evaluation of the registration with six clinical data sets resulted in an accurate localization with a mean displacement of 4.3 mm (/spl plusmn/1 mm) and 3.9 mm (/spl plusmn/1.7 mm) for predicting the lesion position in mammograms and in the MR images, respectively.

A Hardened-by-Design Technique for RF Digital Phase-Locked Loops

Abstract: A RHBD topology for digital phase-locked loops (DPLLs) has been developed for single-event transient (SET) mitigation. By replacing the vulnerable current-based charge pump with a SET-resistant tri-state voltage-switching charge pump and a low-pass filter, the DPLL single-event susceptibility was considerably reduced, while simultaneously decreasing the lock-in time of the DPLL. The design results in a decreased area requirement with minimal impacts on phase jitter and power consumption. Furthermore, the design eliminates the charge pump as the most vulnerable module and significantly hardens the DPLL

A study of the bootstrap method for estimating the accuracy of artificial neural networks in predicting nuclear transient processes

Abstract: The quantification of the uncertainty associated to the results provided by artificial neural networks is essential for their confident and reliable use in practice. This is particularly true for control and safety applications in critical technologies such as those of the nuclear industry. In this paper, the results of a study concerning the use of the bootstrap method for quantifying the uncertainties in the output of supervised neural networks are reported. A thorough parametric analysis is performed with reference to a literature problem. A case study is then provided, concerning the prediction of the feedwater flow rate in a Boiling Water Reactor.

Multiple-Bit Upset in 130 nm CMOS Technology

Abstract: The probability of proton-induced multiple-bit upset (MBU) has increased in highly-scaled technologies because device dimensions are small relative to particle event track size. Both proton-induced single event upset (SEU) and MBU responses have been shown to vary with angle and energy for certain technologies. This work analyzes SEU and MBU in a 130 nm CMOS SRAM in which the single-event response shows a strong dependence on the angle of proton incidence. Current proton testing methods do not account for device orientation relative to the proton beam and, subsequently, error rate prediction assumes no angular dependencies. Proton-induced MBU is expected to increase as integrated circuits continue to scale into the deep sub-micron regime. Consequently, the application of current testing methods will lead to an incorrect prediction of error rates

First results of scintillator readout with silicon photomultiplier

Abstract: A new type of silicon device has been realized that has many properties comparable to, or better than, a conventional PMT (Photomultiplier Tube). This paper presents the first results of using these photodetectors in place of a PMT in the readout of scintillators for possible PET (Positron Emission Tomography) applications. This device, the Silicon Photomultiplier (SiPM), is effectively an avalanche photodiode operated in Geiger mode. In Geiger-mode detectors, a very large current signal is produced regardless of the size of the input, giving just logical rather than proportional information. However, the SiPM is subdivided into a large number (1440) of microcells that act as independent and virtually identical Geiger-mode photodiodes. The outputs of all these individual microcells are connected so that the total output signal is the sum of the signals from all of the microcells that were activated. In this way proportional information can be obtained. As a consequence of their design, these detectors have potentially very fast timing, high gain (105-106) at low bias voltage (~50 V), a high quantum efficiency (35% at 500 nm), excellent single photoelectron resolution and are cheap to manufacture. Here we present results obtained with this new photodetector when used with pulsed LED and scintillator pixels

Efficiencies of coated and perforated semiconductor neutron detectors

Abstract: Previous experimental results indicated that boron-filled perforations within a semiconductor diode detector increase the thermal neutron detection efficiency. In this paper, two basic perforation designs, circular holes and parallel trenches, are analyzed using a simple Monte Carlo model to estimate their potential as high-efficiency thermal neutron detectors. The modeling results indicate that thermal-neutron intrinsic detection efficiencies exceeding 25% can be realized for single coated devices, and efficiencies exceeding 50% can be realized for doubled or "sandwiched" devices.

Numerical Simulation of Radiation Damage Effects in p-Type and n-Type FZ Silicon Detectors

Abstract: In the framework of the CERN-RD50 Collaboration, the adoption of p-type substrates has been proposed as a suitable mean to improve the radiation hardness of silicon detectors up to fluencies of 1times10 16 n/cm2. In this work two numerical simulation models will be presented for p-type and n-type silicon detectors, respectively. A comprehensive analysis of the variation of the effective doping concentration (Neff), the leakage current density and the charge collection efficiency as a function of the fluence has been performed using the Synopsys T-CAD device simulator. The simulated electrical characteristics of irradiated detectors have been compared with experimental measurements extracted from the literature, showing a very good agreement. The predicted behaviour of p-type silicon detectors after irradiation up to 1016 n/cm2 shows better results in terms of charge collection efficiency and full depletion voltage, with respect to n-type material, while comparable behaviour has been observed in terms of leakage current density

The fast neutron response of 4H silicon carbide semiconductor radiation detectors

Abstract: Fast neutron response measurements are reported for radiation detectors based on large-volume SiC p-i-n diodes. Multiple reaction peaks are observed for 14-MeV neutron reactions with the silicon and carbon nuclides in the SiC detector. A high degree of linearity is observed for the /sup 28/Si(n,/spl alpha//sub i/) reaction set of six energy levels in the product /sup 25/Mg nucleus, and pulse height defect differences between the observed /sup 12/C(n,/spl alpha//sub 0/)/sup 28/ Si(n,/spl alpha//sub i/) energy responses are discussed. Energy spectrometry applications in fission and fusion neutron fields are also discussed.

An Area and Power Efficient Radiation Hardened by Design Flip-Flop

Abstract: A radiation hardened by design flip-flop with high single event effect immunity is described. Circuit size and power are reduced by a combination of proven SEE hard techniques, i.e., a temporal latch master and DICE slave are used. Two shift register chains each comprised of 1920 flip-flops have been implemented in the IBM 0.13 mum bulk CMOS process. Measured SEE immunity in accelerated heavy ion testing, and power results are described. A threshold LET over 45 LET (MeV-cm2 /mg) at VDD=1.5 V is demonstrated. High layout density and the likely high LET failure mechanisms are described

Total Ionizing Dose Effects on Triple-Gate FETs

Abstract: This paper investigates the total ionizing dose response of advanced nonplanar triple-gate transistors with short gate length, as a function of device geometry. Experiments and three-dimensional (3-D) simulations using a radiation dedicated code are used to analyze the buildup of a trapped charge in the buried oxide and its impact on the device electrical characteristics. The behaviors of three prospective nonplanar devices are detailed and compared to the total ionizing dose degradation of a planar fully depleted single-gate architecture. The Omega-gate FET is shown to be the most tolerant to a 500 krad(SiO2) total dose exposure thanks to the efficient control provided by the lateral gates over the electrostatic potential throughout the Si film and essentially at the Si fin/BOX interface

Performance evaluation of a subset of a four-layer LSO detector for a small animal DOI PET scanner: jPET-RD

Abstract: Previously, we proposed a new depth of interaction (DOI) encoding method and proved that it worked successfully with four-layered Gd/sub 2/SiO/sub 5/ crystals for a small animal positron emission tomography (PET) detector. We are now planning to develop a small animal PET scanner, jPET-RD (for rodents with DOI detectors), which has both high resolution and high sensitivity by the use of a DOI detector with a 32/spl times/32/spl times/4 crystal array. The scintillator for the detector will be Lu/sub 2(1-x)/Y/sub 2x/SiO/sub 5/ (LYSO). In this work, we evaluated performance of a DOI detector composed of four layers of a 12/spl times/12 LYSO (Lu: 98%, Y: 2%) crystal array by irradiating 511 keV gamma rays uniformly. The new encoding method was used for crystal identification. The size of each crystal was 1.46 mm/spl times/1.46 mm/spl times/4.5 mm. The crystal block was coupled to a 256-channel flat panel position sensitive photomultiplier tube, which has 16/spl times/16 multi anodes at intervals of 3.04 mm. As we expected, all crystals are expressed on a single two-dimensional position histogram without overlapping. Energy resolution of all events is 21.8% and time resolution of all events is 0.69 ns in FWHM. When layers are counted from the top, the energy resolutions of the first, second, third, and fourth layer events are 11.6%, 12.3%, 13.3%, and 19.1% and the time resolutions are 0.60ns, 0.59ns, 0.60ns, and 0.66ns, respectively.

Experimental characterization of monolithic-crystal small animal PET detectors read out by APD arrays

Abstract: Minimizing dead space is one way to increase the detection efficiency of small-animal PET scanners. By using monolithic scintillator crystals (e.g., 20 mm/spl times/10 mm/spl times/10 mm LSO), loss of efficiency due to inter-crystal reflective material is minimized. Readout of such crystals can be performed by means of one or more avalanche photo-diode (APD) arrays optically coupled to the crystal. The entry point of a gamma photon on the crystal surface can be estimated from the measured distribution of the scintillation light over the APD array(s). By estimating the entry point, correction for the depth-of-interaction (DOI) is automatically provided. We are studying the feasibility of such detector modules. To this end, a 64-channel test setup has been developed. Experiments to determine the effect on the spatial resolution of crystal surface finish and detector geometry have been carried out. The first results of these experiments are presented and compared to simulation results. The crystal surface finish has only a small influence on the spatial resolution. The spatial resolution of 20 mm/spl times/10 mm/spl times/10 mm detectors is significantly better when read out on the front side than when read out on the back side. With a 20 mm/spl times/10 mm/spl times/20 mm crystal coupled to two APD arrays, a very small resolution degradation of only /spl sim/0.2 mm is observed for an incidence angle of 30/spl deg/ compared to normal incidence.

The data acquisition system of ClearPET neuro - a small animal PET scanner

Abstract: The Crystal Clear Collaboration has developed a modular system for a small animal PET scanner (ClearPET). The modularity allows the assembly of scanners of different sizes and characteristics in order to satisfy the specific needs of the individual member institutions. The system performs depth of interaction detection by using a phoswich arrangement combining LSO and LuYAP scintillators which are coupled to Multichannel Photomultipliers (PMTs). For each PMT a free running 40 MHz ADC digitizes the signal and the complete scintillation pulse is sampled by an FPGA and sent with 20 MB/s to a PC for preprocessing. The pulse provides information about the gamma energy and the scintillator material which identifies the interaction layer. Furthermore, the exact pulse starting time is obtained from the sampled data. This is important as no hardware coincidence detection is implemented. All single events are recorded and coincidences are identified by software. The system in Ju/spl uml/lich (ClearPET Neuro) is equipped with 10240 crystals on 80 PMTs. The paper will present an overview of the data acquisition system.

PET reconstruction with system matrix derived from point source measurements

Abstract: The quality of images reconstructed by statistical iterative methods depends on an accurate model of the relationship between image space and projection space through the system matrix. The elements of a system matrix on the HiRez scanner from CPS Innovations were acquired by positioning a point source at different positions in the scanner field of view. Then, a whole system matrix was derived by processing the responses in projection space. Such responses included both geometrical and detection physics components of the system matrix. The response was parameterized to correct for point source location, smooth projection noise and the whole system matrix was derived. The model accounts for axial compression (span) used on the scanner. The projection operator for iterative reconstruction was constructed using the estimated response parameters. Computer-generated and acquired data were used to compare reconstruction obtained by the HiRez standard software and that produced by better modeling. Results showed that better resolution and noise property can be achieved with the modeled system matrix.

Anomalous Charge Collection in Silicon Carbide Schottky Barrier Diodes and Resulting Permanent Damage and Single-Event Burnout

Abstract: It was demonstrated that Silicon Carbide Schottky Barrier Diodes exhibited anomalous charge collection with heavy ion irradiation. Consequently, the permanent damage and Single-Event Burnout was observed in spite of no known current sustaining mechanism. A model for the mechanism was proposed based on the device simulation

Single-Event Burnout and Avalanche Characteristics of Power DMOSFETs

Abstract: Analyses of quasi-stationary avalanche simulations on radiation-hardened power MOSFETs suggest that the single-event burnout (SEB) failure is determined by the device's avalanche characteristics and confirm SEB failure mechanism is due to the turn-on of parasitic bipolar transistor. The heavy ion beam is only acting as a trigger. Simulation results on various 600 V and 250 V radiation-hardened power MOSFETs from International Rectifier are compared to an extensive set of single event effect test results and prove quasi-stationary avalanche simulation is capable of evaluating and predicting SEB susceptibility

Analysis of spectroscopic radiation portal monitor data using principal components analysis

Abstract: Many international border crossings screen cargo for illicit nuclear material using radiation portal monitors (RPMs) that measure the gamma-ray flux emitted by vehicles. Screening often consists of primary, which acts as a trip-wire for suspect vehicles, and secondary, which locates the radiation source and performs isotopic identification. The authors present a method of anomaly detection for primary screening that uses past observations of gamma-ray signatures to define an expected benign vehicle population. Newly acquired spectra are then compared to this expected population using statistical criteria that reflect acceptable alarm rates and probabilities of detection. Shown here is an analysis of spectroscopic RPM data collected at an international border crossing using this technique. The raw data were analyzed to develop an expected benign vehicle population by decimating the original pulse-height channels, extracting composite variables with principal components analysis, and estimating variance-weighted distances from the "mean vehicle spectra" with the Mahalanobis distance metric. The following analysis considers data acquired with both NaI(Tl)-based and plastic scintillator-based RPMs. For each system, performance estimates for anomaly sources are compared to common nuisance sources. The algorithm reported here shows promising results in that it is more sensitive to the anomaly sources than common nuisance sources for both RPM types.

Propagating SET Characterization Technique for Digital CMOS Libraries

Abstract: A circuit architecture based on simple logic gates is described which uses small chip areas and low speed testing to characterize single event transients for digital applications. Utility of this architecture is demonstrated with heavy ion data on a 130 nm library

Performance assessment of pixelated LaBr/sub 3/ detector modules for time-of-flight PET

Abstract: Our recent measurements with pixelated LaBr/sub 3/ Anger-logic detectors for use in time-of-flight (TOF) PET have demonstrated excellent energy resolution (5.1% at 511 keV) and coincidence time resolution (313 ps full width at half maximum, FWHM) with small prototype configurations . A full size detector module suitable for a whole-body 3D PET scanner has been constructed based on the prototype designs and consists of 1620 4/spl times/4/spl times/30 mm/sup 3/ LaBr/sub 3/ crystals. We have utilized simulations to guide experimental measurements with the goal of optimizing energy and time resolution in evaluating triggering configurations and pulse shaping needed in a full system. Experimental measurements with the detector module indicate energy and time resolution consistent with our earlier prototypes when measured at low count rate. At very high count rate the energy, time and spatial resolution degrade due to pulse pileup. While it is possible to reduce pulse pileup by using smaller photomultiplier tubes (i.e., 39 mm instead of 50 mm diameter), we are trying to limit the total number of PMTs needed for a full-scale PET scanner with a large axial field-of-view. Therefore, we have designed and tested a pulse shaping circuit to improve the detector response and performance at high count rate. Simulations of a complete LaBr/sub 3/ scanner indicate significant improvements in noise equivalent count rate (NEC) and spatial resolution can be achieved using pulse shaping.

Radiation Detection Properties of 4H-SiC Schottky Diodes Irradiated Up to $10^16$ n/cm $^2$ by 1 MeV Neutrons

Abstract: We report the results of an experimental study on the radiation hardness of 4H-SiC diodes used as alpha-particle detectors with 1 MeV neutrons up to a fluence of 8times1015 n/cm2. As the irradiation level approaches the range 1015 n/cm2 , the material behaves as intrinsic due to a very high compensation effect and the diodes are still able to detect with a reasonable good Charge Collection Efficiency (CCE=80%). For fluences >1015 n/cm2 CCE decreases monotonically to ap20% at the highest fluence. Heavily irradiated SiC diodes have been studied by means of Photo Induced Current Transient Spectroscopy (PICTS) technique in order to characterize the electronic levels associated with the irradiation-induced defects. The dominant features of the PICTS spectra occur between 400-700 K; in this temperature range the deep levels associated with the induced defects play the main role in degradation of the CCE. Enthalpy, capture cross-section and concentration of such deep levels were calculated and we found that two deep levels (Et=1.18 eV and Et=1.50 eV) are responsible for the decrease in CCE. They have been associated to an elementary defect involving a carbon vacancy and to a defect complex involving a carbon and a silicon vacancy, respectively