In this paper, we discuss hard x-ray optics, in general, and lobster-eye focusing optics, in particular, for concealed object
detection, at longer distances. The longer distance (~50m) scenario is important for Improvised Explosives Detection
(IED), "seeing through walls," "seeing objects under ground," and related applications.
There is a worldwide need for efficient inspection of cargo containers at airports, seaports and road border crossings. The main objectives are the detection of contraband such as illicit drugs, explosives and weapons. Due to the large volume of cargo passing through Australia's airports every day, it is critical that any scanning system should be capable of working on unpacked or consolidated cargo, taking at most 1-2 minutes per container. CSIRO has developed a fast-neutron/gamma-ray radiography (FNGR) method for the rapid screening of air freight. By combining radiographs obtained using 14 MeV neutrons and 60Co gamma-rays, high resolution images showing both density and material composition are obtained. A near full-scale prototype scanner has been successfully tested in the laboratory. With the support of the Australian Customs Service, a full-scale scanner has recently been installed and commissioned at Brisbane International Airport.
For evaluating the contents of trucks, containers, cargo, and passenger vehicles by a non-intrusive gamma-ray or X-ray imaging system to determine the possible presence of contraband, three-dimensional (3D) measurements could provide more information than 2D measurements. In this paper, a linear pushbroom scanning model is built for such a commonly used gamma-ray or x-ray cargo inspection system. Accurate 3D measurements of the objects inside a cargo can be
obtained by using two such scanning systems with different scanning angles to construct a pushbroom stereo system. A simple but robust calibration method is proposed to find the important parameters of the linear pushbroom sensors. Then, a fast and automated stereo matching algorithm based on free-form deformable registration is developed to obtain 3D measurements of the objects under inspection. A user interface is designed for 3D visualization of the objects in interests. Experimental results of sensor calibration, stereo matching, 3D measurements and visualization of a 3D cargo container and the objects inside, are presented.
The EURopean Illicit TRAfficing Countermeasures Kit project is part of the 6th European Union Framework Program,
and aims at developing a neutron inspection system for detecting threat materials (explosives, drugs, etc.) in cargo
containers. Neutron interaction in the container produces specific gamma-rays used to determine the chemical
composition of the inspected material. An associated particle sealed tube neutron generator is developed to allow precise
location of the interaction point by direction and time-of-flight measurements of the neutrons tagged by alpha-particles.
The EURITRACK project consists in developing: a transportable deuterium-tritium neutron generator including a
position sensitive alpha detector (8×8 matrix of YAP:Ce crystals coupled to a multi-anode photomultiplier), fast neutron
and gamma-ray detectors, front-end electronics to perform coincidence and spectroscopic measurements, and an
integrated software which manages neutron generator and detectors positioning, data acquisition and analysis. Hardware
components have been developed and tested by the consortium partners. Current status of this work and provisional
performances of the system assessed by Monte Carlo calculations are presented.
Portable device for explosives' detection (SENNA) based on Nanosecond Neutron Analysis (NNA) / Associated Particles Technique (APT) has been created and tested. SENNA is a single suitcase weighting 35 kg; it is remotely controlled from any PC-compatible computer. Inside is an APT neutron generator with a 3×3 matrix of semiconductor detectors of associated alpha-particles, two BGO-based detectors of gamma-rays, fully-digital data acquisition electronics, data analysis and decision-making software, and batteries. Detection technology is based on determining chemical composition of the concealed substance by analyzing secondary gamma-rays from interaction of tagged fast neutrons with its material. A combination of position-sensitive alpha-detector and time-of-flight analysis allows one to determine the location of the detected material within the inspected volume and its approximate mass. Fully digital data acquisition electronics is capable of performing alpha-gamma coincidence analysis at very high counting rates, which leads to reduction of the detection time down to dozens of seconds. SENNA's scenario-driven automatic decisionmaking algorithm based of "fuzzy logic" mechanism allows one to detect not only standard military or industrial explosives, but also improvised explosives (including those containing no nitrogen), even if their chemical composition differs from that of standard explosives. SENNA can also be "trained" to detect other hazardous materials, such as chemical/toxic materials, if their chemical composition is in any way different from that of the surrounding materials.
When neutrons interact with nuclei, the resulting energy of the interaction can be released in the form of gamma rays, whose energy is characteristic of the nucleus involved in the reaction. The PELAN (Pulsed Elemental Analysis with Neutrons) system uses a pulsed neutron generator and an integral thermalizing shield that induce reactions that cover most of the entire neutron energy range. The neutron generator uses a d-T reaction, which releases fast 14 MeV neutrons responsible for providing information on chemical elements such as C, N, and O. During the time period between pulses, the fast neutrons undergo multiple elastic and inelastic interactions that lower their energy making them easier to be captured by chemical elements, such as H and Cl. The PELAN system has been used for a number of applications where non-intrusive, non-destructive interrogation is needed. This report illustrates examples of its performance in interrogations for unexploded ordnance (UXO), landmines, large vehicle bombs and illicit drug detection.
Compact Marx generators based on the wave-erection principle are ideal drivers for flash x-ray systems. Traditional Marx generator design techniques lead to slow rising voltage pulses, marked by high impedances, large temporal jitter values and inefficient transfer of energy. As a result, larger pulse generators are fabricated to overcome these shortcomings, which results in excessive volumes and weights. Applied Physical Electronics, L.C. has been developing Marx generators for many years based on the wave-erection principle. As a result, generators with relatively low source impedances, high impulse voltages and compact geometries are making their way into use as portable flash x-ray drivers. More recently, APELC is extending their compact designs into complete flash x-ray systems, including the diode load. This paper discusses two generator systems that have been developed, basic diode geometries that will be incorporated, and a new novel system designed to generate up to an x-ray energy of 3.2 MeV.
A new neutron interrogation technique for detection of concealed Special Nuclear Material (SNM) is
described. This technique is a combination of timing techniques from pulsed prompt gamma neutron activation analysis
with silicon carbide (SiC) semiconductor fast neutron detector technology. SiC detectors are a new class of radiation
detectors that are ultra-fast and capable of processing high count rates. SiC detectors can operate during and within
nanoseconds of the end of an intense neutron pulse, providing the ability to detect the prompt neutron emissions from
fission events produced by the neutrons in concealed SNM on a much faster pulsing time scale than has been achieved
by other techniques.
Neutron-induced fission neutrons in 235U have been observed in the time intervals between pulses of 14-MeV
neutrons from a deuterium-tritium electronic neutron generator. Initial measurements have emphasized the detection of
SNM using thermal-neutron induced fission. Neutron pulsing and time-sequenced neutron counts were carried out on a
hundreds of microseconds time scale, enabling the observation of prompt fission neutrons induced by the die-away of
thermal neutrons following the 14-MeV pulse. A discussion of pulsed prompt-neutron measurements and of SiC
detectors as well as initial measurement results will be presented.
Compton imagers offer a method for passive detection of nuclear material over background radiation. A prototype Compton imager has been constructed using 8 layers of silicon detectors. Each layer consists of a 2×2 array of 2 mm thick cross-strip double-sided silicon detectors with active areas of 5.7 × 5.7 cm2 and 64 strips per side. The detectors are daisy-chained together in the array so that only 256 channels of electronics are needed to read-out each layer of the instrument. This imager is a prototype for a large, high-efficiency Compton imager that will meet operational requirements of Homeland Security for detection of shielded uranium. The instrument can differentiate between different radioisotopes using the reconstructed gamma-ray energy and can also show the location of the emissions with respect to the detector location. Results from the current instrument as well as simulations of the next generation instrument are presented.
Photons with energies above 6 MeV can be used to detect small amounts of nuclear material inside large cargo containers. The method consists in using an intense beam of high-energy photons (bremsstrahlung radiation) in order to induce reactions of photofission on actinides. The measurement of delayed neutrons and delayed gammas emitted by fission products brings specific information on localization and quantification of the nuclear material. A simultaneous measurement of both of these delayed signals can overcome some important limitations due to matrix effects like heavy shielding and/or the presence of light elements as hydrogen. We have a long experience in the field of nuclear waste package characterization by photon interrogation and we have demonstrated that presently the detection limit can be less than one gram of actinide per ton of package. Recently we tried to extend our knowledge to assess the performance of this method for the detection of special nuclear materials in sea and air freights. This paper presents our first results based on experimental measurements carried out in the SAPHIR facility, which houses a linear electron accelerator with the energy range from 15 MeV to 30 MeV. Our experiments were also modeled using the full scale Monte Carlo techniques. In addition, and in a more general frame, due to the lack of consistent data on photonuclear reactions, we have been working on the development of a new photonuclear activation file (PAF), which includes cross sections for more than 600 isotopes including photofission fragment distributions and delayed neutron tables for actinides. Therefore, this work includes also some experimental results obtained at the ELSA electron accelerator, which is more adapted for precise basic nuclear data measurements.
We report on recent progress in the development of the Fast Neutron Imaging Telescope (FNIT), a detector with both imaging and energy measurement capabilities, sensitive to neutrons in the 2-20 MeV range. FNIT was initially conceived to study solar neutrons as a candidate design for the Solar Sentinels program under formulation at NASA. This instrument is now being configured to locate fission neutron sources for homeland security purposes. By accurately identifying the position of the neutron source with imaging techniques and reconstructing the energy spectrum of fission neutrons, FNIT can locate problematic amounts of Special Nuclear Material (SNM), including heavily shielded and masked samples. The detection principle is based on multiple elastic neutron-proton (n-p) scatterings in organic scintillators. By reconstructing the n-p event locations and sequence and measuring the recoil proton energies, the direction and energy spectrum of the primary neutron flux can be determined and neutron point sources identified. The performance of FNIT is being evaluated through a series of Monte Carlo simulations and lab tests of detector prototypes. The Science Model One (SM1) of this instrument was recently assembled and is presently undergoing performance testing.
The detection of shielded special nuclear materials is of great concern to the homeland security community. It is a challenging task that typically requires large detectors arrays to achieve the required sensitivity to detect shielded enriched uranium. We simulated the performance of three different configurations of scintillation detectors in a realistic gamma ray background. The simulations were performed using the GEANT4 simulation package fine tuned for low energy photon transport. The background spectrum was obtained by modeling high-resolution background spectra obtained by various groups in various locations. The performance of a non-imaging scintillating array was compared to the performance of two imaging arrays: a coded aperture imager and a Compton imager. The sensitivity was modeled at three energies for the emission from a 1 kg sphere of uranium enriched to 95% U-235: the 185 keV emission from U-235, the 1001 keV emission from U-238, and the 2614 keV emission from U-232. The instruments were modeled with and without passive shielding. The most detectable signal is the 2.614 MeV emission from U-232 contamination if present at a level greater than tens of parts per trillion. While the non-imaging array has the highest efficiency, it also has the highest background rate and is therefore not the most sensitive instrument. We present the expected performance for the three different configurations.
The Florida Institute for Nuclear Detection and Security (FINDS) is currently working on the design and evaluation of a prototype neutron detector array that may be used for parcel screening systems and homeland security applications. In order to maximize neutron detector response over a wide spectrum of energies, moderator materials of different compositions and amounts are required, and can be optimized through 3-D discrete ordinates and Monte Carlo model simulations verified through measurement. Pu-Be sources can be used as didactic source materials to augment the design, optimization, and construction of detector arrays with proper characterization via transport analysis. To perform the assessments of the Pu-Be Source Capsule, 3-D radiation transport computations are used, including Monte Carlo (MCNP5) and deterministic (PENTRAN) methodologies. In establishing source geometry, we based our model on available source schematic data. Because both the MCNP5 and PENTRAN codes begin with source neutrons, exothermic (α,n) reactions are modeled using the SCALE5 code from ORNL to define the energy spectrum and the decay of the source. We combined our computational results with experimental data to fully validate our computational schemes, tools and models. Results from our computational models will then be used with experiment to generate a mosaic of the radiation spectrum. Finally, we discuss follow-up studies that highlight response optimization efforts in designing, building, and testing an array of detectors with varying moderators/thicknesses tagged to specific responses predicted using 3-D radiation transport models to augment special nuclear materials detection.
NIRST is a pushbroom scanning infrared radiometer that makes use of 512×2 arrays of resistive microbolometers. This instrument comprises mainly two cameras, one operating in the spectral band of 3.4-4.2 μm (band 1) and the other in the bands of 10.4-11.3 (band 2) and 11.4-12.3 μm (band 3). It is intended for the retrievals of forest fire and sea surface temperatures in the Aquarius / SAC-D mission. In this mission the satellite will be launched into a Sun Synchronous polar orbit with an ascending node at 6 PM. This orbit suits the need of discriminating forest fires from solar reflections. NIRST is designed to achieve a spatial resolution of 350 m and a swath width of 180 km at nadir. Its field of view can be steered across track up to 500 km on each side to shorten the revisit time.
To measure fire intensity temperatures NIRST will perform multispectral scans of ground area in bands 1 and 2 and the acquired data will be analyzed using a double band algorithm. The microbolometer detectors have been designed to exhibit useful dynamic range for this application. It is projected that the detector response in band 1 saturates only when NIRST scans a 350 m ground pixel of average temperature of 700 K. The use of the data acquired in bands 2 and 3 allows for the retrieval of sea surface temperature by means of the split algorithm technique.