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Methods and apparatus involving neutron resonance radiography are used to map the elemental composition of an object. Sets of neutrons having energies within particular energy bands are directed through an object to be imaged. The attenuation of the neutrons passed through the object is detected, and that data can be used to detect explosives, weapons, drugs and other contraband.

The uranium neutron coincidence collar uses thermal neutron interrogation to verify the 235U mass in low-enriched uranium (LEU) fuel assemblies in fuel fabrication facilities. Burnable poisons are ...

RadiaBeam has developed a novel, flexible linac for electrons and X-rays (FLEX) capable of energy variation from 2 to 9 MeV within a single RF pulse. This accelerator employs a robust traveling wave accelerating structure with a large energy and power acceptance that allows the unique features of deep energy and current variation required for novel adaptive cargo inspection techniques and Computed Tomography. Robust RF and water-cooling systems allow average beam powers up to 15 kW, upgradable to 57 kW, at 6 MeV, potentially making this accelerator useful for electron beam irradiation applications. The high peak currents of the electron beam produced by FLEX enable novel FLASH radiotherapy methods with fast dose delivery. In this paper, we present the linac design and its components, as well the results of the experimental demonstration of beam acceleration with energy variation.

Active neutron coincidence systems are commonly used by international inspectorates to verify a material balance across the various stages of the nuclear fuel cycle. The Uranium Neutron Coincidence Collar (UNCL) is one such instrument; it is used to measure the linear density of 235U (g 235U/cm of active length in assembly) in fresh light water reactor fuel in nuclear fuel fabrication facilities. The UNCL and other active neutron interrogation detectors have historically relied on americium lithium (241AmLi) sources to induce fission within the sample in question. Californium-252 is under consideration as a possible alternative to the traditional 241AmLi source. This work relied upon a combination of experiments and Monte Carlo simulations to demonstrate the technical basis for the replacement of 241AmLi sources with 252Cf sources by evaluating the statistical uncertainty in the measurements incurred by each source and assessing the penetrability of neutrons from each source for the UNCL.

Detection of cross-border smuggling of illicit materials and contraband is a challenge that requires rapid, low-dose, and efficient radiographic technology. The work we describe here is derived from a technique which uses monoenergetic gamma rays from low energy nuclear reactions, such as 11B(d,nγ)12C, to perform radiographic analysis of shipping containers. Transmission ratios of multiple monoenergetic gamma lines resulting from several gamma producing nuclear reactions can be employed to detect materials of high atomic number (Z), the details of which will be described in a separate paper. Inherent in this particular nuclear reaction is the production of fast neutrons which could enable neutron radiography and further characterization of the effective-Z of the cargo, especially within the range of lower Z. Previous research efforts focused on the use of total neutron counts in combination with X-ray radiography to characterize the hydrogenous content of the cargo. We present a technique of performing transmitted neutron spectral analysis to reconstruct the effective Z and potentially the density of the cargo. This is made possible by the large differences in the energy dependence of neutron scattering cross-sections between hydrogenous materials and those of higher Z. These dependencies result in harder transmission spectra for hydrogenous cargoes than those of non-hydrogenous cargoes. Such observed differences can then be used to classify the cargo based on its hydrogenous content. The studies presented in this paper demonstrate that such techniques are feasible and can provide a contribution to cargo security, especially when used in concert with gamma radiography.

Recently Silicon Photomultipliers (SiPMs) have become well recognized as the detector of choice for various applications which demand good photon number resolution and time resolution of short weak light pulses in the nanosecond time scale. In the case of longer and more intensive light pulses, SiPM performance gradually degrades due to dark noise, afterpulsing, and non-instant cell recovering. Nevertheless, SiPM benefits are expected to overbalance their drawbacks in applications such as X-ray cargo inspection using Scintillation-Cherenkov detectors and accelerator beam loss monitoring with Cherenkov fibres, where light pulses of a microsecond time scale have to be detected with good amplitude and timing resolution in a wide dynamic range of 105–106. This report is focused on transient characteristics of a SiPM response on a long rectangular light pulse with special attention to moderate and high light intensities above the linear dynamic range. An analytical model of the transient response and an initial consideration of experimental results in comparison with the model are presented.

X-ray Computed Tomography (CT) is a widely used tool for security and industrial non-destructive testing (NDT). Scanned objects in these uses typically contain multiple materials with different atomic numbers. In these cases, Dual-Energy CT (DECT) has numerous advantages over conventional single-energy CT, including improved image quality, reduction of effect of scatter and other artefacts, and better material decomposition. Therefore, DECT has become the standard for inspection of objects containing multiple materials [1–2]. In this paper, we present a new CT technology: Adaptive Computed Tomography with Modulated-energy X-ray pulses (ACTM) [3]. ACTM is based on adaptive cargo radiography techniques [4–6] that have been developed over the last few years. To perform CT imaging, we propose to utilize the exact and fast Katsevich image reconstruction algorithm [7–12].Key enabling ACTM techniques are:•Linear accelerator with deep energy control.•Multi-energy spectrum in each slice provided by packets of short X-ray pulses with end-point energy ramp up (> 1 MHz rate of energy switching).•Fast detectors with reduced sensitivity to scatter radiation.•Detector readout with silicon photomultipliers (SiPM) provides time-resolved measurement of short X-ray pulses.•Electronics and an algorithm for automatic, dynamic adjustment of SiPM responsivity in detector channels provides increased dynamic range of X-ray imaging.•Real-time algorithm for X-ray pulse-by-pulse selection of high and low energy windows for dual-energy material decomposition.•Filtered Backprojection (FBP) helical image reconstruction based on the theoretically exact Katsevich algorithm.The ACTM method for dual- (or, multi-) energy CT mitigates the main disadvantages of the conventional interlaced approach:•Ambiguity and artifacts caused by sampling different regions due to motion of the object between interlaced pulses with distinct energies.•Distortion of CT image of the boundaries between regions with large difference in Z.•Small range of object thicknesses where material decomposition is valid.

At the request of the Domestic Nuclear Detection Office (DNDO), a Study Committee comprised of representatives from the American Physical Society, Panel on Public Affairs, the IEEE, and Nuclear and Plasma Sciences Society performed a technical review of the DNDO Transformational and Applied Research Directorate (TARD) R&D program. TARD's principal objective is to address gaps in the Global Nuclear Detection Architecture (GNDA) through improvements in the performance, cost, and operational burden of detectors and systems. The charge to the Study Committee was to investigate the existing TARD R&D plan and portfolio, recommend changes to the existing plan, and recommend possible new R&D areas and opportunities. This report is the result of an independent, detailed analysis of the current R&D plan and includes, for each application area, observations, and recommendations to focus future investments within the context of the TARD mission.

The security market requirements for state-of-the-art mobile and portal radiography inspection systems include high imaging resolution (better than 5 mm line pair), penetration beyond 300 mm steel equivalent, material discrimination (three groups of Z) at speeds up to 16 km/h with 100% image sampling, low dose and small radiation exclusion zone. New research into radiography methods and systems has been actively pursued in order to achieve these challenging requirements. Recently, a significant portion of the R&D effort has been devoted to re-examining betatron based X-ray inspection systems. The advantages of the betatron-based inspection systems over conventional linac-based designs include small focal spot (which improves resolution), low weight and form-factor, a simpler control system and relatively low cost. A novel, low-dose Multi-Energy Betatron-based Cargo Inspection System, MEBCIS, presented in this paper relies on an innovative technique of extracting two X-ray pulses with lower-and higher-energies within a single betatron acceleration cycle (in contrast to conventional dual-energy betatrons with one X-ray pulse produced during separate betatron acceleration cycles). In addition to the new betatron, new types of fast X-ray Scintillation-Cherenkov detectors, rapid processing of detector signals, an adaptive detector feedback algorithm for control of the betatron, and algorithms for intelligent material discrimination are parts of the overall MEBCIS system. The key advantage of the MEBCIS concept is that the material discrimination data is acquired in a single scan line rather than two. Thus, for the same betatron pulse rate, the scan rate can be twice as fast (better throughput) or can be done with a lower dose, even without adaptive dynamic pulse adjustment. Application of these techniques will maximize material discrimination, penetration, and contrast resolution while simultaneously reducing dose to the environment, resulting in a smaller exclusion zone. Its minimal size and weight will allow MEBCIS to be placed on a lightweight truck chassis.

The Dark Matter Time Projection Chamber (DMTPC) collaboration is developing a low-pressure gas TPC for detecting WIMP-nucleon interactions. DMTPC detectors use optical readout with CCD cameras to search for the daily modulation of the directional signal of the dark matter wind. An analysis of several charge readout channels has been developed to obtain additional information about ionization events in the detector. In order to reach sensitivities required for the WIMP detection, the detector needs to minimize backgrounds from electron recoils. This article shows that by using the readout of charge signals in addition to CCD readout, a preliminary statistics-limited 90% C.L. upper limit on the γ and e[superscript −] rejection factor of 5.6 × 10[superscript −6] is obtained for energies between 40 keV[subscript ee] and 200 keV[subscript ee]., United States. Dept. of Energy (Grant DE-FG02-05ER41360), United States. Dept. of Energy. Advanced Detector Research Program (Contract 6916448), Massachusetts Institute of Technology. James H. Ferry Fund for Innovation in Research Education, MIT Department of Physics Pappalardo Program, Massachusetts Institute of Technology (Charles E. Reed Faculty Initiative Fund), Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology. Department of Physics, Bates Linear Accelerator Center

Radioscintigraphic imaging during sentinel lymph node (SLN) mapping could potentially improve localization; however, parallel-hole collimators have certain limitations. In this study, we explored the use of coded aperture (CA) collimators.Equations were derived for the six major dependent variables of CA collimators (i.e., masks) as a function of the ten major independent variables, and an optimized mask was fabricated. After validation, dual-modality CA and near-infrared (NIR) fluorescence SLN mapping were performed in pigs.Mask optimization required the judicious balance of competing dependent variables, resulting in sensitivity of 0.35%, XY resolution of 2.0 mm, and Z resolution of 4.2 mm at an 11.5-cm field of view. The findings in pigs suggested that NIR fluorescence imaging and CA radioscintigraphy could be complementary, but present difficult technical challenges.This study lays the foundation for using CA collimation for SLN mapping, and also exposes several problems that require further investigation.

The trimodal imager (TMI) images gamma-ray sources from a mobile platform using both coded aperture (CA) and Compton imaging (CI) modalities. In this paper we will discuss development and performance of image reconstruction algorithms for the TMI. In order to develop algorithms in parallel with detector hardware we are using a GEANT4 [J. Allison, K. Amako, J. Apostolakis, H. Araujo, P.A. Dubois, M. Asai, G. Barrand, R. Capra, S. Chauvie, R. Chytracek, G. Cirrone, G. Cooperman, G. Cosmo, G. Cuttone, G. Daquino, et al., IEEE Trans. Nucl. Sci. NS-53 (1) (2006) 270] based simulation package to produce realistic data sets for code development. The simulation code incorporates detailed detector modeling, contributions from natural background radiation, and validation of simulation results against measured data. Maximum likelihood algorithms for both imaging methods are discussed, as well as a hybrid imaging algorithm wherein CA and CI information is fused to generate a higher fidelity reconstruction.

Direction measurement of weakly interacting massive particles in time-projection chambers can provide definite evidence of their existence and help to determine their properties. This article demonstrates several concepts for charge amplification in time-projection chambers that can be used in direction-sensitive dark matter search experiments. We demonstrate reconstruction of the 'head-tail' effect for nuclear recoils above 100keV, and discuss the detector performance in the context of dark matter detection and scaling to large detector volumes., 15 pages, 9 figures

We report on tests of a radionuclide imaging system for in vivo investigations in small animals with low-energy photons as from 125-I (27–35 keV). Imaging optics features a high-resolution coded aperture mask and a fine pitch hybrid pixel detector (silicon 300- micron or 700- micron thick, or CdTe 1 mm thick) of the Medipix2 series (55 micron pitch, 256X256 pixels). The coded aperture had 480 70- micron holes in 100- micron-thick tungsten. Laboratory tests with a 109-Cd 22 keV source and a microfocus X-ray tube (35 kVp, Mo anode) show a system resolution of about 110 micron at magnification m= 2.12 and a sensitivity improvement of 30:1 as compared to a 300- micron pinhole collimator. The field of view also depends on magnification: in the experiments presented, it varied from 6 mm ( m= 2.12) to 21 mm (m = 0.66). 125-I in vivo mouse thyroid imaging with the 70 micron coded aperture, a 300 micron pinhole and a 100 micron parallel hole collimator was also performed to obtain a qualitative comparison. This low energy, semiconductor-based, compact gamma-ray imaging system can be used as a gamma-ray sub-millimeter resolution imager for energies below about 35 keV and it is the basic imaging unit of a small animal Single Photon Emission Computed Tomography system (MediSPECT) built at University of Napoli Federico II and Istituto Nazionale Fisica Nucleare (INFN), Napoli.

High-performance large area imaging detectors for fast neutrons in the 5–14 MeV energy range do not exist at present. The aim of this project is to combine microchannel plates or MCPs (or similar electron multiplication structures) traditionally used in image intensifiers and X-ray detectors with amorphous silicon (a-Si) pixel arrays to produce a composite converter and intensifier position sensitive imaging system. This detector will provide an order of magnitude improvement in image resolution when compared with current millimetre resolution limits obtained using phosphor or scintillator-based hydrogen rich converters. In this study we present the results of the initial experimental evaluation of the prototype system. This study was carried out using a medical X-ray source for the proof of concept tests, the next phase will involve neutron imaging tests. The hybrid detector described in this study is a unique development and paves the way for large area position sensitive detectors consisting of MCP or microsphere plate detectors and a-Si or polysilicon pixel arrays. Applications include neutron and X-ray imaging for terrestrial applications. The technology could be extended to space instrumentation for X-ray astronomy.

We report on the tests of a prototype (MediSPECT) system developed at University & INFN Napoli, for Single Photon Emission Computed Tomography (SPECT) imaging on small animals with a small Field of View (FoV) and high spatial resolution. MediSPECT is a SPECT imaging system based on a 1-mm-thick CdTe pixel detector, bump-bonded to the Medipix2 CMOS readout circuit operating in single-photon counting. The CdTe detector has 256×256 square array of pixels arranged with a 55 μm pitch, for a sensitive area of 14×14 mm 2 . In its present version, this system implements a single detector head, mounted on a rotating gantry. For preliminary testing and calibration of the acquisition equipment and image reconstruction algorithms, 90 projections of a γ-ray point source ( 109 Cd) through a single pinhole (diameter 0.4 mm; radius of rotation about 2.5 cm; focal length about 4.5 cm) were acquired for 20 min each in a step-and-shoot mode. Capillaries, 800 μm in diameter, were arranged in a Y-shape to form a more complex phantom ( 125 I, 1 mm pinhole diameter, 45 projections, each acquired for 25 min). Images were reconstructed with a custom algorithm implementing standard OS-EM with center of rotation correction and spatial resolution of 0.2 mm over a FoV of 2 mm was obtained.

The security market requirements for high throughput rail cargo radiography inspection systems include better than 5 mm line pair imaging resolution, penetration beyond 400 mm steel equivalent, scan speeds of up to 60 km/h, material discrimination (four groups of Z) in 100 % of cargo at speeds reaching 45 km/h, low dose and small radiation exclusioi zone. In order to achieve these requirements, which cannot be met t conventional dual energy radiography systems, a team lead by RadiaBeam Technologies, LLC (RBT) has initiated a research into new radiography methods and imaging detector materials with the goal of developing an Adaptive Railroad Cargo Inspection System (ARCIS). The ARCIS technical concept relies on linac-based, adaptive, ramped energy source of packets of short X-ray pulses sampled by a new type of fast X-ray detectors with rapid hardware processing for intelligent linac control, and advanced radiography image processing and material discrimination analysis. The following ARCIS key enabling technologies overcome the limitations of the conventional dual energy interlaced cargo inspection systems: • Multi-energy material discrimination in a single scan line provided by packets of short pulses from an X-ray source with end-point energy ramp up (> 1 MHz rate of energy switching); • Real-time intelligent setting of packet's maximum energy depend on X-ray attenuation in cargo; • Fast Scintillation-Cherenkov detectors with reduced sensitivity to scatter radiation; • Detector readout with Silicon Photomultiplier (SiPM) provides time-resolving of short X-ray pulses; • Self-control adaptive dynamic adjustment of SiPM responsivity in detector channel for increased dynamic range.

This paper presents an overview of the engineering upgrades being made to optimize the AIMS diagnostic on the Alcator C-Mod tokamak, a novel, particle accelerator-based diagnostic that can nondestructively measure the evolution of material surface compositions inside magnetic fusion devices. Three major AIMS subsystems are presented: the RFQ deuteron accelerator; the particle detectors; and the Alcator C-Mod tokamak. The combined results of the upgrades will enable AIMS to routinely map critical plasma-material interaction quantities, such as net erosion/redeposition and fusion fuel retention, over large areas of PFC surfaces between plasma shots and after the run day.

We have recently completed a large-area, coded-aperture, gamma-ray imager for use in searching for radiation sources. The instrument was constructed to verify that weak point sources can be detected at considerable distances if one uses imaging to overcome fluctuations in the natural background. The instrument uses a rank-19, one-dimensional coded aperture to cast shadow patterns onto a 0.57 m/sup 2/ NaI(Tl) detector composed of 57 individual cubes each 10 cm on a side. These are arranged in a 19/spl times/3 array. The mask is composed of four-cm thick, one-meter high, 10-cm wide lead blocks. The instrument is mounted in the back of a small truck from which images are obtained as one drives through a region. Results of first measurements obtained with the system are presented.

High-performance large-area imaging detectors for fast neutrons in the 5–14 MeV energy range do not exist at present. The aim of this project is to combine microchannel plates or MCPs (or similar electron multiplication structures) traditionally used in image intensifiers and X-ray detectors with amorphous silicon pixel arrays to produce a composite converter and intensifier position-sensitive imaging system. This detector will provide an order of magnitude improvement in image resolution when compared with current millimetre resolution limits obtained using phosphor- or scintillator-based hydrogen-rich converters. In this study the detection of fast neutrons is based on neutron capture in silicon rather than proton recoil in hydrogen-rich converters. This will reduce the effect that light spreading has on image resolution when using conventional phosphor-based converters. The threshold in the silicon capture cross-section will reduce the effect of neutron scatter on the detectability of small features in fast neutron radiographs. In this study we highlight the prototype detector design, present its main advantages and the current status of the detector build phase.

Geological processes on Earth can be related to those that may have occurred in past epochs on Mars, if analytical methods used on Earth can be operated remotely on the surface of the Red Planet. Nuclear analytical techniques commonly used in terrestrial geology are neutron activation analysis (NAA) and gamma-ray spectroscopy (GRS), which determine the elemental composition, elemental concentration and stratigraphical distribution of water in rocks and soils. We describe a detector concept called GEORAD (GEOlogical and RADiation environment package) for the proposed ExoMars rover within the ESA's Aurora Programme for the exploration of the Solar System. GEORAD consists of a compact neutron source for the NAA of rocks and soils and a GRS. The GRS has a dual role since it can be used for natural radioactivity studies and NAA. A fully depleted silicon detector coupled to neutron sensitive converters measures the solar particle and neutron flux interacting with the Martian surface. We describe how the GEORAD detector suite could contribute to the geological and biological characterisation of Mars both for the detection of extinct or extant life and to evaluate potential hazards facing future manned missions. We show how GEORAD measurements complement the astrobiological objectives of the Aurora programme.

Recent events highlight the increased risk of a terrorist attack using either a nuclear or a radiological weapon. One of the key needs to counter such a threat is long-range detection of nuclear material. Theoretically, gamma-ray emissions from such material should allow passive detection to distances greater than 100 m. However, detection at this range has long been thought impractical due to spatially fluctuating levels of natural background radiation. These fluctuations are the major source of uncertainty in detection and mean that sensitivity cannot be increased simply by increasing detector size. Recent work has shown that this problem can be overcome through the use of imaging techniques. In this paper we describe the background problems, the advantages of imaging and the construction of a prototype, large-area (0.57 m/sup 2/) gamma-ray imager to detect nuclear materials at distances of /spl sim/ 100 m.

In vivo imaging of pharmaceuticals labeled with radionuclides has proven to be a powerful tool in human subjects. The same imaging methods have often been applied to small animal but usually only within the nuclear medicine (NM) community, and usually only to evaluate the efficacy of new radiopharmaceuticals. We have built a compact mini gamma camera, a pixellated array of NaI(Tl) crystals coupled to 3′′ R2486 Hamamatsu Position Sensitive PMT; in combination with a pinhole collimator, which allows for high resolution in vivo SPECT imaging. Calculations show that reasonable counting rates are possible. The system has been tested and preliminary measurements on mice have been done. The performances of the camera are in the expectations. Improvements will be done both on the collimation technique and on the detector. Simulations have been performed to study a coded aperture collimator. The results show that the efficiency can be greatly improved without sacrificing the spatial resolution. A dedicated mask has been designed and will be used soon.

We introduce and demonstrate the utility of coded aperture (CA) nuclear scintigraphy for imaging small animals. CA imaging uses multiple pinholes in a carefully designed mask pattern, mounted on a conventional gamma camera. System performance was assessed using point sources and phantoms, while several animal experiments were performed to test the usefulness of the imaging system in vivo, with commonly used radiopharmaceuticals. The sensitivity of the CA system for 99m Tc was 4.2 � 10 3 cps/Bq (9400 cpm/MCi), compared to 4.4 � 10 4 cps/Bq (990 cpm/MCi) for a conventional collimator system. The system resolution was 1.7 mm, as compared to 4 – 6 mm for the conventional imaging system (using a high-sensitivity low-energy collimator). Animal imaging demonstrated artifact-free imaging with superior resolution and image quality compared to conventional collimator images in several mouse and rat models. We conclude that: (a) CA imaging is a useful nuclear imaging technique for small animal imaging. The advantage in signalto-noise can be traded to achieve higher resolution, decreased dose or reduced imaging time. (b) CA imaging works best for images where activity is concentrated in small volumes; a low count outline may be better demonstrated using conventional collimator imaging. Thus, CA imaging should be viewed as a technique to complement rather than replace traditional nuclear imaging methods. (c) CA hardware and software can be readily adapted to existing gamma cameras, making their implementation a relatively inexpensive retrofit to most systems. Mol Imaging (2002) 1, 344 – 353.

Fast neutron resonance radiography (NRR) has been devised as an elemental imaging method with applications such as contraband detection and mineral analysis. In NRR, a two-dimensional (2-D) elemental mapping of hydrogen, carbon, nitrogen, oxygen, and the sum of other elements is obtained from fast neutron radiographic images, taken at different neutron energies and chosen to cover the resonance cross-section features of one or more elements. Images are formed using a lens-coupled plastic scintillator charged coupled device (CCD) combination. In preliminary experiments, we have produced NRR images of various simulants using a variable energy beam based on the Li(p,n)Be reaction and a variable energy proton beam. As an alternative to this method, we have studied NRR imaging using the D-D reaction, d(d,He)n, at fixed incident D energy and scanning through various neutron energies by using the angular variation in neutron energy. The object and detector rotate together around the neutron source; different energy (2-6 MeV) neutrons can be obtained at different angles from the target. The radiographic transmission image provides a 2-D mapping of the sum of elemental contents (weighted by the attenuation coefficients). Transmission measurements taken at different neutron energies (angles) then form a set of linear equations, which can then be solved to map individual elemental contents.

Coded apertures have been investigated in the past for their promise of an improved signal-to-noise ratio (SNR) over pinhole and collimator systems. We describe a coded aperture camera designed for high-resolution (1.66-mm) imaging of low energy (140 keV) gamma-ray emitters with a conventional Anger camera. The aperture pattern was chosen to maximize the SNR and to allow a simple implementation of a new near-field artifact compensation technique based on the use of an antisymmetric array. Experimental results show that coded aperture imaging can produce good quality high-resolution planar images with high SNR while keeping exposure times and injected doses at reasonable levels.

During a Nuclear Medicine project that called for the optimal design of a coded aperture we found that lowthroughput masks do not always provide a Signal-to-Noise Ratio (SNR) advantage. In this paper, we present the simulations of the performance of some coded aperture patterns chosen from different families and compare the results with theoretical predictions. A general expression for the SNR and its particular form for different patterns are provided. The choice of the optimal pattern family is discussed with reference to the characteristics of the object to be imaged and in light of the effect of near-field artifacts. No-Two-Holes-Touching (NTHT) arrays based on Modified Uniformly Redundant Arrays (MURAs) proved to offer the best compromise between SNR performance and practical fabrication constraints. r 2001 Elsevier Science B.V. All rights reserved.

An X-ray computed tomography (CT) system was developed for monitoring the solidification front in metal casting. The X-ray source was a 6 MeV linear accelerator (linac) emitting photons in 5 µs pulses at a rate of 180 Hz. The source intensity was 300 R/min at 1 m. The X-ray beam was collimated in a 30 deg fan shape with a 10-mm height. A detector array comprising 128 elements was located 845 mm from the source. Pure aluminum in a clay-graphite crucible (178-mm o.d., 146-mm i.d.) was melted in a resistance heater furnace, and a cooling tube at the center of the crucible solidified the molten aluminum to simulate the casting process. A solidification front formed around the tube and progressed outward over an hour until the aluminum was completely solidified. X-ray attenuation measurements were taken every minute during this time. Density images were later reconstructed from these measurements using CT. From these images, the progression of the solidification front was determined with a planar resolution of 1.3 mm and a sensitivity of 3.7 pct. The density maps agree with expected values and correlate well with temperature measurements obtained independently by thermocouples.

A non-invasive sensor based on high-energy x-ray computed tomography has been developed for monitoring the progression of solidification in metal casting. The sensor comprised a 6 MeV linear accelerator and a 128-channel CdWO 4 detector array. Laboratory experiments were performed on cylindrical castings of pure aluminum and its alloys. The sensor produced a series of time-lapse images showing the movement of the liquid/solid interface during solidification. The solidification front was imaged every two minutes with a planar spatial resolution of 1.6 mm and a contrast sensitivity of 1.5%. The tomography results agreed well with those obtained by thermocouple measurements.

Existing requirements for high throughput cargo radiography inspection include high resolution images (better than 5 mm line pair resolution), penetration beyond 400 mm steel equivalent, material discrimination (organic, inorganic, high Z), high scan speeds (> 10kph, up to 60kph), low dose and small radiation exclusion zone; all in a cost effective system. To meet and exceed these requirements research into a number of new radiography methods has been initiated. Novel concepts relying on intrapulse modulated energy X-ray sources, mono-energetic gamma-ray sources, and new types of fast X-ray detectors, Scintillation-Cherenkov Detectors, are expected to be more beneficial being combined with unique features of Silicon Photomultiplier (SiPM) technology.

We have developed a neutron detection system for accelerator based neutron radiography and tomography based on a combination of scintillation screen and large aperture optics and a cooled CCD camera. The system is capable of detecting single neutron events and can therefore be considered as a possible detector for neutron scattering as well as conventional imaging. The system has a resolution of 0.1 mm or 1242/spl times/1152 pixels. The limit of image size is set by the light output of the scintillator, the light collection of the optical system, the size of the CCD and the desired signal to noise ratio. The lower limit on neutron flux is determined by the dark current of the chip. Equations for these limits have been derived and can be used to predict and optimize performance. The scintillation light output per incident neutron is large enough to permit the use of lens coupled systems with their increased flexibility and ease of implementation. The system can approach a quantum limited noise level, depending on the particular geometry used. For our current system, based on the use of NE-426 scintillator, a 1242/spl times/1152 pixel (27.9/spl times/25.9 mm) EEV 05-30 CCD operating at -50 C, and using a 100 mm focal length, F/0.9 lens, the maximum size for the imaging screen is 0.7 m (based on 10 photoelectrons for a single detected neutron), and the lower limit for flux is 0.1 n/pixel/s based on this size screen and a typical dark current of 1 e/pixel/s.

In the continuous and semi-continuous casting of metals and alloys, the shape and location of the solidification front greatly affect the quality of castings. Yet, there is no real-time sensor available to the casting industry for monitoring the solidification front. A recently invented three-dimensional imaging technique for tracking the liquid/solid interface in the solidifying casting is presented. Issues involved in the application of the technique to the feedback control of continuous casting processes are also addressed.

A neutron spectroscopic technique for plutonium content measurement is described. The technique exploits the kinematic cutoff of neutron emission in (α,n) reactions on oxygen. The Watt spectrum of fission neutron emission extends to higher energies without such a cutoff. 4He scintillation detectors were calibrated with an energy cut to reject neutrons of low energies, thereby making the detectors sensitive only to fission neutrons but not to neutrons from the (a,n) reaction on oxygen.

Water-based Cherenkov counters are considered for remote detection of special nuclear materials with aid of active interrogation. We designed and manufactured a detector capable of gamma ray detection and demonstrated particle energy discrimination ability. Background reduction techniques based on energy threshold and photomultiplier tube multiplicity were implemented in particle detection. Both approaches resulted in a significant suppression of low-level background.

High energy protons can be a powerful probe for standoff detection of Special Nuclear Materials (SNM). In particular, the use of protons of 500 MeV and up with modest beam currents, 10 to 100 μA, can be far more efficient in the production of fission neutrons than conventional bremsstrahlung based electron linacs. Such beams can provide both the range and, more importantly, the sensitivity to fissile materials required for remote detection at distances of hundreds of meters or more. The practical application of this technique has been limited by the requirements of producing such high energy protons using conventional proton accelerators—typically very large, fixed installations. The on‐going development at MIT of a new generation of very compact superconducting cyclotrons makes a compelling case for examining this approach for a practical standoff detection system where large numbers of neutrons can be produced using an accelerator with ∼1 GeV energy and modest beam currents in the 1 to 100 μA range. We will describe current work in the design of a 250 MeV, 1 mA superconducting accelerator and its extension to higher energies, and make estimates of sensitivity to reasonable amounts of shielded fissile material.

many nondestructive testing applications, high resolution images are desired of large engineering superstructures, such as aircraft. Traditionally, this is done by sequentially imaging small segments of the objects using small area detectors. Recently, we have developed a position sensitive neutron detector system using a LiF-ZnS scintillator screen and a cooled charge coupled device (CCD) camera. Large arrays of these individual detectors can be assembled to image large areas simultaneously at high resolution. For tomography, radiographs are obtained from multiple viewing angles with the large area detector. Tomographic reconstruction of large arrays is prohibitively time consuming and has several associated practical problems. By using the inherent segmentation of the detector, the reconstruction problem can be reduced to one of several small area reconstructions performed in parallel. A parallel tomographic reconstruction scheme based on segmented arrays is presented. It is shown that the parallel algorithm produces images that are identical to images produced without segmentation, however, using smaller individual arrays. The intrinsically parallel segmented array reconstruction provides a means of rapidly reconstructing images of any dimension using small, tractable arrays. An N x N two-dimensional tomographic reconstruction can be performed with m individual detector segments and m2 processors each reconstructing 2N/m x 2 x N/m image segments. This approach is demonstrated for neutron tomography; however, it is applicable to any tomographic imaging problem.

The Dark Matter Time Projection Chamber (DMTPC) is a low pressure (75 Torr CF 4 ) 10 liter detector capable of measuring the vector direction of nuclear recoils with the goal of directional dark matter detection. In this Letter we present the first dark matter limit from DMTPC from a surface run at MIT. In an analysis window of 80-200 keV recoil energy, based on a 35.7 g-day exposure, we set a 90% C.L. upper limit on the spin-dependent WIMP-proton cross section of 2.0×10 -33 cm2 for 115 GeV/c 2 dark matter particle mass. Keywords: Dark matter; WIMP; Direction-sensitive; Time projection chamber, United States. Department of Energy (Contract 6916448)

We present the case for a dark matter detector with directional sensitivity. This document was developed at the 2009 CYGNUS workshop on directional dark matter detection, and contains contributions from theorists and experimental groups in the field. We describe the need for a dark matter detector with directional sensitivity; each directional dark matter experiment presents their project's status; and we close with a feasibility study for scaling up to a one ton directional detector, which would cost around $150M., 48 pages, 37 figures, whitepaper on direct dark matter detection with directional sensitivity

We show data from a new type of detector that can be used to determine the neutron flux, the energy distribution, and the direction of motion neutron for both fast and thermal neutrons. Many neutron detectors are plagued by large backgrounds from X-rays and gamma rays, and most current neutron detectors lack single-event energy sensitivity or any information on neutron directionality. Even the best detectors are limited by cosmic ray neutron backgrounds. All applications (neutron scattering and radiography, measurements of solar and cosmic ray neutron flux, measurements of neutron interaction cross-sections, monitoring of neutrons at nuclear facilities, oil exploration, and searches for fissile weapons of mass destruction) will benefit from the improved neutron detection sensitivity and improved measurements of neutron properties made possible by this detector. The detector is free of backgrounds from X-rays, gamma rays, beta particles, relativistic singely charged particles, and cosmic ray neutrons. It is sensitive to thermal neutrons, fission neutrons, and high energy neutrons with detection features distinctive for each energy range. It is capable of determining the location of a source of fission neutrons based on the characteristics of elastic scattering of neutrons by helium nuclei. The detector we have constructed could identify 1 g of reactor grade plutonium, 1 m away, with less than 1 min of observation time., National Science Foundation (U.S.), United States. Dept. of Energy, Massachusetts Institute of Technology. Dept. of Physics, United States. Dept. of Homeland Security, Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies

The Raytheon Trimodal Imager (TMI) uses coded aperture and Compton imaging technologies as well as the nonimaging shadow technology to locate an SNM or radiological threat in the presence of background. The heart of the TMI is two arrays of NaI crystals. The front array serves as both a coded aperture and the first scatterer for Compton imaging. It is made of 35 5x5x2" crystals with specially designed low profile PMTs. The back array is made of 30 2.5x3x24" position-sensitive crystals which are read out at both ends. These crystals are specially treated to provide the required position resolution at the best possible energy resolution. Both arrays of detectors are supported by aluminum superstructures. These have been efficiently designed to allow a wide field of view and to provide adequate support to the crystals to permit use of the TMI as a vehicle-mounted, field-deployable system. Each PMT has a locally mounted high-voltage supply that is remotely controlled. Each detector is connected to a dedicated FPGA which performs automated gain alignment and energy calibration, event timing and diagnostic health checking. Data are streamed, eventby- event, from each of the 65 detector FPGAs to one master FPGA. The master FPGA acts both as a synchronization clock, and as an event sorting unit. Event sorting involves stamping events as singles or as coincidences, based on the approximately instantaneous detector hit pattern. Coincidence determination by the master FPGA provides a pre-sorting for the events that will ultimately be used in the Compton imaging and coded aperture imaging algorithms. All data acquisition electronics have been custom designed for the TMI.

The Raytheon Trimodal Imager (TMI) uses coded aperture and Compton imaging technologies as well as the nonimaging shadow technology to locate an SNM or radiological threat in the presence of background. The coded aperture imaging is useful for locating and identifying radiological threats as these threats generally emit lower energy gammas whereas the Compton imaging is useful for SNM threats as in addition to low energy gammas which can be shielded, SNM threats emit higher energy gammas as well. The shadow imaging technology utilizes the structure of the instrument and its vehicle as shadow masks for the individual detectors which shadow changes as the vehicle moves through the environment. Before a radioactive source comes into the fields of view of the imagers it will appear as a shadow cast on the individual detectors themselves. This gives the operator advanced notice that the instrument is approaching something that is radiological and on which side of the vehicle it is located. The two nuclear images will be fused into a combined nuclear image along with isotope ID. This combined image will be further fused with a real-time image of the locale where the vehicle is passing. A satellite image of the locale will also be made available. This instrument is being developed for the Standoff Radiation Detection System (SORDS) program being conducted by Domestic Nuclear Detection Office (DNDO) of the Department of Homeland Security (DHS).

A prototype position-sensitive neutron detector was designed and built for two- and three-dimensional tomographic imaging of materials and complex assemblies. The detector system consists of an LiF-ZnS scintillator screen optically coupled to a cooled charge-coupled device (CCD). Practical resolution limits of the single-screen system were calculated to be approximately 100 mu m, determined by the neutron-beam divergence and the resolution of the scintillator screen. Contrast resolution in a (200- mu m)/sup 3/ volume element was calculated to be 1% of the cross section in small samples. The system included the MIT Research Reactor as a thermal neutron source (nominal flux approximately 2.4*10/sup 8/ n degrees /cm-/sup 2/s), a rotating sample holder, and the two-dimensional position-sensitive detector. The effects of scatter were estimated and compared to data. Two- and three-dimensional tomograms of phantoms and several demonstration objects, including a control valve and an oil well dolomite core sample, were obtained. >

This paper presents a measurement of the ratio of photon to electron production and the scintillation spectrum in a popular gas for time pro jection chambers, carbon tetrafluoride (CF4), over the range of 200 to 800 nm; the ratio is measured to be 0.34+/-0.04. This result is of particular importance for a new generation of dark matter time projection chambers with directional sensitivity which use CF4 as a fill gas., 19 pages, including appendix. 8 figures

We present new results with a prototype detector that is being developed by the DMTPC collaboration for the measurement of the direction tag (head-tail) of dark matter wind. We use neutrons from a Cf-252 source to create low-momentum nuclear recoils in elastic scattering with the residual gas nuclei. The recoil track is imaged in low-pressure time-projection chamber with optical readout. We measure the ionization rate along the recoil trajectory, which allows us to determine the direction tag of the incoming neutrons., Comment: Contributed to the International Conference on Topics in Astroparticle and Underground Physics (TAUP) 2007, Sendai, Japan (3 pages, 4 figures)