An X-ray mine imaging system (XMIS) that uses a new form of backscatter x-ray radiography developed at the University of Florida was successfully field-tested at Fort A.P. Hill, Virginia in October, 2001. The XMIS obtained high quality images of both anti-tank and anti-personnel mines on several of the Fort A.P. Hill test lanes. For high resolution imaging at a power level of 750 watts, total time for scanning and for processed image acquisition was about 60 s for a 0.5 x 0.5 m area. The very good imaging results obtained from the initial field tests with the XMIS demonstrate the excellent capabilities of this system as a confirmation sensor for land mine detection. Critical to the success of the XMIS is the use of both collimated and uncollimated detectors. This yields system capabilities and performance that cannot be matched by using only uncollimated detectors with coded apertures and spatial filters to deconvolve system response. The initial field tests showed that some fairly simple modifications could significantly improve the performance of the XMIS. With the modifications, high resolution scanning of a 0.5 x 0.5 m area can be done in 20 to 30 seconds at a power level of around 300 watts.
An overview and sample images from AS&E's recently deployed Radioactive Threat Detection equipment offered as an option to its MobileSearch x-ray inspection systems. Detector technology, signal processing, threat location and identification strategies are presented, as well as this system's unique ability to perform RTD while performing backscatter and transmission x-ray inspection.
A compact mobile single sided vehicle inspection system is presented employing backscatter x-ray imaging. Major system components are described as well as its intended applications. Sample images are shown from recent scans of small and large vehicles at a range of scan speeds and distances. Various types of contraband and threat types are shown to be detected.
The X-ray screening of luggage by aviation security personnel may be badly hindered by the lack of visual cues to depth in an image that has been produced by transmitted radiation. Two-dimensional "shadowgraphs" with "organic" and "metallic" objects encoded using two different colors (usually orange and blue) are still in common use. In the context of luggage screening there are no reliable cues to depth present in individual shadowgraph X-ray images. Therefore, the screener is required to convert the 'zero depth resolution' shadowgraph into a three-dimensional mental picture to be able to interpret the relative spatial relationship of the objects under inspection. Consequently, additional cognitive processing is required e.g. integration, inference and memory. However, these processes can lead to serious misinterpretations of the actual physical structure being examined. This paper describes the development of a stereoscopic imaging technique enabling the screener to utilise binocular stereopsis and kinetic depth to enhance their interpretation of the actual nature of the objects under examination. Further work has led to the development of a technique to combine parallax data (to calculate the thickness of a target material) with the results of a basis material subtraction technique to approximate the target's effective atomic number and density. This has been achieved in preliminary experiments with a novel spatially interleaved dual-energy sensor which reduces the number of scintillation elements required by 50% in comparison to conventional sensor configurations.
A simple ionization absolute humidity gauge was developed in the present study. It consisted of a parallel plate ionization chamber with a radioactive alpha-ray source for supplying ion pairs to measure absolute humidity in air and an operational amplifier circuit for measuring the ionization current of the order of 10-12 A produced by alpha-particles. A sealed alpha-ray soure, 241Am, was used. The size of the gauge was 50 mm in diameter and 130mm in length. The distance between the two electrodes in the chamber was set at 15 mm which was enough longer distance than the maximum range of attenuated alpha-particles from the source and the wall effect on the ionization current was removed. The ionization current of the gauge was measured at various humidities in a range from 0 g/m3 to 25 g/m3 and temperatures in the range from 20°C to 40°C under the atmospheric pressure. It was shown that the ionization current is inversely proportional to the absolute humidity because a decrease in the ionization current is caused by the absolute amount of water vapor contained in the air. From the relationship between the absolute humidity and the ionization current, it was found that the absolute humidity could be measured with a sensitivity of 0.4 g/m3 that is equal to 3% in relative humidity at 20°C. The continual measurement of absolute humidity was carried out to confirm the performance of the gauge.
A new Compton X-ray backscatter imaging (CBI) technique called lateral migration radiography (LMR) is applied to detecting a class of sub-surface defects in materials and structures of industrial importance. Examples are delamination in layered composite structures, defects in deposited coatings on metal surfaces such as in aircraft jet engine components and geometrical structural/composition changes (e.g. due to corrosion)on the inside of shell-like components with only outside surface area access. LMR scans on aircraft samples showed intensity decreases of up to 25% in corroded areas relative to intensities in clean areas. Especially significant were scans of samples that were performed with the clean or uncorroded side facing up. The corrosion on the opposite side of these 2 mm thick samples, where there was contact between the frame member and the aircraft skin, was clearly visible. Scans of other samples showed that LMR is capable of detecting small flaws on the inside of shell-like components with only outside surface area access. Cracks around a fastener hole that were ~ 15 mm in length and no more than 0.25 mm in width were seen through the aircraft skin. Scans of an aluminum honeycomb structure demonstrated that LMR is also capable of picking up internal defects that include crushed core and debonding zones.
Applicability of fused silica core optical fibers to in-reactor dosimetry was demonstrated at elevated temperatures and a special irradiation rig was developed for realizing high-temperature optical dosimetry in a High Temperature Test Reactor (HTTR) in Oarai Research Establishment of JAERI (Japan Atomic Energy Research Institute). The paper will describe present status of preparation for the high temperature dosimetry in HTTR, utilizing radiation-resistant optical fibers and radioluminescent materials. Temperature measurement with a high-speed response is a main target for the present optical dosimetry, which could be applied for monitoring transient behaviors of the HTTR. This could be realized by measuring intensity of thermoluminescence and black body radiation in infrared region. For monitoring reactor powers, optical measurements in visible region are essential. At present, measurement of intensity of Cerenkov radiation will be most promising. Other possibilities with radio-luminescent materials having luminescent peaks in visible region are under survey. One of the candidates will be silica, which has a robust radioluminescent peak at 450 nm.
We report further studies on the neutron detection capabilities of boron carbide/Si heterjunction diodes. In particular, we investigate the behavior of these diodes in the presence of low neutron flux. The spectrum is compared with previous data obtained in the high neutron flux environment in the irradiation sample well of a TRIGA reactor.
Applications of neutron diffraction for small samples (<1mm3) or small fiducial areas are limited by the
available neutron flux density. Recent demonstrations of convergent beam electron and x-ray diffraction and focusing of cold (λ>1 Å) neutrons suggest the possibility to use convergent beam neutron diffraction for small sample crystallography. We have carried out a systematic study of diffraction of both monoenergetic and broad bandwidth
neutrons at the NIST Research Reactor and at the Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory. Combining convergent beams with time-of-flight Laue diffraction is particularly attractive for high efficiency small sample diffraction studies. We have studied single crystal and powder diffraction of neutrons with convergence angles as large as 15° and have observed diffracted peak intensity gains greater than 20. The convergent beam method (CBM) shows promise for crystallography on small samples of small to medium size molecules (potentially even for proteins), ultra-high pressure samples, and for mapping of strain and texture distributions in larger samples.
Neutron moderation land mine detection involves irradiating the ground with fast neutrons and subsequently detecting the thermalized neutrons which return. This technique has been studied since the 1950s, but only using non-imaging detectors. Without imaging, natural variations in moisture content, surface irregularities and sensor height variations produce sufficient false alarms to render the method impractical in all but the driest conditions. This paper describes research to design and build a prototype land mine detector based on neutron moderation imaging. The detector consists of a novel thermal neutron imaging system, a unique neutron source to uniformly irradiate the underlying ground, and hardware and software for image generation and enhancement. A proof-of-principle imager has been built, but with a very weak point source offset from the detector to roughly approximate a uniform source at the detector plane. Imagery of mine surrogates is presented. Realistic Monte Carlo simulations were used to estimate performance capability, including spatial resolution and detection times.
Mutual repulsion of discrete charged particles or Coulomb repulsion is widely considered to be an ultimate hard limit in charged particle optics. It prevents the ability to finely focus high current beams into a small spots at large distances from the defining apertures. A classic example is the 1970s era “Star Wars” study of an electron beam directed energy weapon as an orbiting antiballistic missile device. After much analysis, it was considered physically impossible to focus a 1000-amp 1-GeV beam into a 1-cm diameter spot 1000-km from the beam generator. The main reason was that a 1-cm diameter beam would spread to 5-m diameter at 1000-km due to Coulomb repulsion. Since this could not be overcome, the idea was abandoned. But is this true? What if the rays were reversed? That is, start with a 5-m beam converging slightly with the same nonuniform angular and energy distribution as the electrons from the original problem were spreading at 1000-km distance. Could Coulomb repulsion be overcome? Looking at the terms in computational studies, some are reversible while others are not. Since the nonreversible terms should be small, it might be possible to construct an electron beam directed energy weapon.
An attempt has been made, for the first time, to extend the capabilities of diffraction enhanced imaging (DEI) using low
concentrations of a contrast agent. A phantom has been constructed to accommodate a systematic series of diluted bromine deoxyuridase (BrDU) samples in liquid form. This was imaged using a conventional DEI arrangement and at a range of energies traversing the Br K-edge. The images were analyzed to provide a quantitative measure of contrast as a function of X-ray energy and (BrDU) concentration. The results indicate that the particular experimental arrangement was not optimized to exploit the potential of this contrast enhancement and several suggestions are discussed to improve this further.
A new thermal neutron imaging system has been constructed, based on a 20-cm x 17-cm He-3 position-sensitive detector with spatial resolution better than 1 mm. New compact custom-designed position-decoding electronics are employed, as well as high-precision cadmium masks with Modified Uniformly Redundant Array patterns. Fast Fourier Transform algorithms are incorporated into the deconvolution software to provide rapid conversion of shadowgrams into real images. The system demonstrates the principles for locating sources of thermal neutrons by a stand-off technique, as well as visualizing the shapes of nearby sources. The data acquisition time could potentially be reduced two orders of magnitude by building larger detectors.
Ion induced luminescence was studied for SiO2 glasses and SiO2 based optical fiber materials with different hydrogen and oxyhydrate concentration. The luminescence of the visible wavelengths was measured during the irradiation of protons and also heavier ions with low (5~10 keV) and high (0.2 ~ 2 MeV)energies, at a temperature rane between 295 and 600 K. Hydrogen concentration profiles were also examined by the ion beam analysis techniques to compare the nominal OH values. In addition to a prominent broad peak of 460 nm, characteristic peaks were detected at around 390 nm and 660 nm, depending on the OH contents. For fused silica specimens with lower OH, however, a peak at 390 nm was found at a small dose and its intensity decreased quickly with an increase of the ion dose. For synthesized silica with higher OH concentration, a small peak was found at 650 nm, corresponding to the non-bonding-oxygen-hole-center, while the 390 peak not appeared. Except for the low-OH synthesized silica, there existed a large amount of hydrogen, which does not form OH. The origin of the luminescence and the damage process will be discussed in connection with the nuclear and electronic energy loss by the penetrating energetic ions.
Radioluminescence from rare earth oxide materials was measured in the visible wavelength range and the range from 1000 to 3000 nm in an ion beam accelerator and a fission reactor of Japan Materials Testing Reactor (JMTR). In erbium oxide, peaks at 560, 660, and 1540 nm were observed by the proton beam irradiation, and the complicated luminescence peaks around 1800 and 2000 nm were observed by the proton beam irradiation and at the reactor full power operation of 50 MW. The peaks at 560, 660, and 1540 nm are attributed to the electron transition between the energy levels of Er3+ ions. The complicated luminescences observed in JMTR were quenched with the irradiation time elapsed, though the intensity was not changed by the irradiation of the proton beam of 2.6 x 1013 p/cm2s. It was considered that the precursors for the complicated luminescent peaks around 1800 and 2000 nm disappeared under the neutrons irradiation.
Significant effort currently is being devoted to the development of noninvasive imaging systems that allow in vivo assessment of biological and biomolecular interactions in mice and other small animals. While physiological function in small animals can be localized and imaged using conventional radionuclide imaging techniques such as single-photon emission tomography (SPECT) and positron emission tomography (PET), these techniques inherently are limited to spatial resolutions of 1-2 mm. For this reason, we are developing a small animal radionuclide imaging system (SARIS) using grazing incidence optics to focus gamma-rays emitted by 125I and other radiopharmaceuticals. We have developed a prototype optic with sufficient accuracy and precision to focus the 27.5 keV photons from 125I onto a high-resolution imaging detector. Experimental measurements from the prototype have demonstrated that the optic can focus X-rays from a microfocus X-ray tube to a spot having physical dimensions (approximately 1500 microns half-power diameter) consistent with those predicted by theory. Our theoretical and numerical analysis also indicate that an optic can be designed and build that ultimately can achieve 100 μm spatial resolution with sufficient efficiency to perform it in vivo single photon emission imaging studies in small animal.
DirectRay direct-conversion digital x-ray-imaging detectors using selenium exhibit high sensitivity and resolution to x-ray energies just below the K-fluorescence edge compared to energies just above. Detector sensitivity and self-protected dynamic range can be manipulated by modifying dielectric thickness and selenium electric field. Replacing the dielectric layer with a charge-transport layer (CTL) allows a faster cycle time, lower residual-image charge, improved signal to noise ratio, and better operating stability. The new CTL structure allows fast multi-frame imaging, enabling applications such as dual-energy subtraction, tomosynthesis, and dynamic imaging (fluoroscopy).
We report on a new x-ray converter screen based on the powdered Lu2O3:Eu scintillator. Lu2O3:Eu offers high density (9.4 g/cm3), high average atomic number (63), and a peak emission of 610 nm. The high density of the material and a high packing fraction of the coating provide higher x-ray absorption efficiency, even with thin screens. As a result Lu2O3:Eu screens are expected to provide superior spatial resolution and x-ray stopping power compared to commercial powdered screens. This newly developed screen has excellent imaging performance and offers several practical advantages such as ease of fabrication, low cost, and durability. This paper will discuss preliminary results of the imaging performance of this novel screen.
In this study we present Vista-Mamma 50, a novel detection system for high resolution real-time digital mammography. A matrix sensor (12 cm x 12 cm) consists of a high luminance CsI:Tl crystal grown with columnar structure on the top of a pin photodiode matrix driven by CMOS transistors. This imaging technology is known to allow achievement of a pixel size as small as 50 μm or less with a fill factor of the sensitive area of about 80%. The sensor is equipped with a fast real-time electronic system for readout and digitization of images with a dynamic range of 12 bits. Images can be obtained at a frame rate as high as 9 images per second in a 4 x 4 binning operation mode. Appropriate computerized control tools, real-time image treatment, data representation and off-line analysis have been developed. On-line image processing is automatically applied to each frame, including offset and gain corrections and masking of defective pixels. Quantitative measurements including dose response, modulation transfer function (MTF) and detective quantum efficiency are presented. It was found that the detector response shows linear dependence on the entrance dose. The results from the MTF showed that a resolution of equal to or greater than 8 lp/mm could be achieved. The high value of the DQE obtained could be ascribed to the large fill factor. The high resolution detector that we present is well adapted to the image quality which is required by the standards for applications in mammography. Some preliminary results have been obtained for microcalcifications performed on equivalent breast phantoms. Clinical tests are in progress.
This paper discusses the issue of calibration for the growing number of electronic displays used in the filmless and electronic radiology departments. It concentrates on CRT and LCD displays as these are the most matured electronic display systems available at this time. It is shown that grayscale calibration is necessary and useful to optimally display the information contained in the various digital images in diagnostic radiology. In addition properties and drawbacks of four prevalent standards for display function have been discussed.
A summary is given of methods to manipulate the polychromatic radiation emitted from electron impact x-ray sources so as to generate a (quasi-)monochromatic beam. These methods include: differential attenuation of bremsstrahlung, differential reflection of x-rays from monochromating crystals, production of fluorescence x-rays from secondary targets and geometrical enhancement of characteristic radiation. Typical values for some of the parameters which characterize (quasi-)monochromatic sources i.e. monochromaticity, energy bandwidth and source radiance are presented. A brief description is given of some radiological techniques which either necessitate or benefit from monochromatic radiation. With the help of a figure of merit for monochromatic x-ray sources, the suitability of the candidates mentioned above for these techniques is assessed.
We demonstrate that 80-140 keV hard X-rays from the X-ray star Cygnus X-1 could be used, in principle, to image the interior of an unknown target spacecraft. A simulated radiograph shows good signal-to-noise in a 1000-second exposure with ~2 cm spatial resolution. Because of the high collimation and short wavelength of the radiation, an image can be formed at almost any target-detector distance. Practical application of the technique would require the detector spacecraft to assume a parallel trajectory with the target and maintain station accurately enough to hold the radiograph shadow on its sensitive surface. Further research is needed on 1) detector background minimization in high-latitude and high-altitude orbits; 2) image formation for rotating targets, which is a problem similar to computerized tomography; and 3) optimization of navigation and station-keeping.