A new Compton backscatter imaging (CBI) technique, described as lateral migration radiography (LMR), has been developed and applied successfully to two difficult diagnostic problems: Detection of buried, plastic landmines, and detection of material flaws which lie close to, and parallel to, a surface, the method is based on image contrast generated by alteration of photon lateral migration relative to the illuminating beam direction. It is extraordinarily sensitive to density and/or atomic number variation along the photon lateral-direction travel paths. In LMR, relevant information-carrying photon detection efficiencies are two to three orders-of-magnitude greater than other CBI techniques such that the electric energy requirement for x-ray generation is only about one joule per acquired image pixel. The resulting small product of pixel illumination dwell time and x-ray generator electric power implies that current, easily accessible technology can be used to fabricate LMR systems with practical usage protocols. Three have been designed and built at the University of Florida: A laboratory device for perfecting buried landmine acquisition; a mobile system for field-demonstrating landmine detection; and, a laboratory system for detection of material defects in small structural parts. The LMR images, acquired in a laboratory landmine detection setting, are so definitive that identification of the mine-type, as well as presence, can be often accomplished. Results of a field test are near-perfect, both in determining buried landmine presence and in lack of false positive response. Images acquired in material flaw detection indicate ability to detect lateral cracks or delaminations with thickness less than 100 microns, as well as corrosion on surfaces between layers of structural sheets. These applications provide evidence of the viability of a new, one-sided x-ray radiography technique which images hidden structures of objects which have here-to-fore been difficult, or impossible, to detect with practical image aquisition times.

It is our goal to develop a coded aperture based X-ray backscatter imaging detector that will provide sufficient speed, contrast and spatial resolution to detect Antipersonnel Landmines and Improvised Explosive Devices (IED). While our final objective is to field a hand-held detector, we have currently constrained ourselves to a design that can be fielded on a small robotic platform. Coded aperture imaging has been used by the observational gamma astronomy community for a number of years. However, it has been the recent advances in the field of medical nuclear imaging which has allowed for the application of the technique to a backscatter scenario. In addition, driven by requirements in medical applications, advances in X-ray detection are continually being made, and detectors are now being produced that are faster, cheaper and lighter than those only a decade ago. With these advances, a coded aperture hand-held imaging system has only recently become a possibility. This paper will begin with an introduction to the technique, identify recent advances which have made this approach possible, present a simulated example case, and conclude with a discussion on future work.

The characterization in the bulk of crystalline thick materials (thickness: several cm) can be performed up to now by using high energy X-Ray sources (gamma ray diffractometers or high energy beamlines of synchrotron facilities) or with neutron beams. The Institut Laue-Langevin has developed and built in collaboration with the Laboratoire de Spectrométrie Physique, a new instrument using the continuous high energy X-ray spectrum (100 - 400 keV) delivered by a high voltage, fine focus X-ray generator, previously used for industrial radiography. This article describes the principle of this new diffractometer and presents an overview of the main applications in the field of non destructive crystalline characterization, for both physic researches and industrial applications.

Fast Neutron Resonance Radiography (NRR) has been devised as an elemental imaging method, with applications such as contraband detection and mineral analysis. In the NRR method, a 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 chosen to cover the resonance cross section features of one or more elements. Images are formed using a lens-coupled plastic scintillator-CCD combination. In preliminary experiments, we have produced NRR images of various simulants using a variable energy neutron beam based on the Li(p,n)Be reaction and a variable energy proton beam. In order to overcome practical limitations to this method, we have studied NRR imaging using the D-D reaction at a fixed incident D energy and scanning through various neutron energies by using the angular variation in neutron energy. The object-detector assembly rotates around the neutron source and different energy (2-6 MeV) neutrons can be obtained at different angles from a D-D neutron source. The radiographic 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) form a set of linear equations, which can then be solved to map individual elemental contents.

PELAN (Pulsed ELemental Analsys with Neutrons) is a man-portable system for the detection of explosives and chemical warfare agents, weighing 40 kg. It is based on the principle that explosives and other contraband contain various chemical elements such as H, C, N, O, etc. in quantities and ratios that differentiate them from ot her innocuous substances. The pulsed neutrons are produced with a pulsed 14 MeV (d-T) neutron generator. Separate gamma-ray spectra from fast neutron, thermal neutron and activation reactions are accumulated and analyzed to determine elemental content. Data analysis is performed in an automatic manner and a final result of whether a threat is present is returned to the operator. Since 1999, PELAN has undergone several field trials and demonstrations, including in 2001, demonstrations in Belgium andin the US of its ability to identify chemical warfare agents. We will review the results of these tests and also discuss the modifications made to the system.

A modular 2 MeV Shaped Energy™ system complemented with two 220 keV scanning pencil beam systems is described. With the scanning x-ray pencil beams providing backscatter imaging, this multi-source system has excellent detection capabilities, low radiation dose, and a small footprint for inspecting air cargo containers in a crowded airport environment. Its design is based on a prototype inspection system with a 3.5 MeV Shaped Energy source and segmented transmission detector complemented with two 450 keV scanning pencil beam systems. This higher energy system was designed for very high density cargo such as fully loaded ISO shipping containers. The unique modular design provides maximum detection with minimum radiation because both the Shaped Energy system and the lower energy systems can be independently optimized. Moreover, the combination of high-resolution transmission coupled with backscatter provides increased probability of detecting threats. A novel configuration of these same modules could be applied to a proposed CT air cargo inspection system with true density determining capabilities. Sample images from the existing 3.5 MeV prototype system will be presented along with recent test results.

A novel 3D X-ray imaging technique to enhance the visual interpretation of complex X-ray images routinely encountered in aviation security applications has been developed. The 3D information is visualised as a smooth object rotation on a video display monitor. Further work enabled motion parallax to be combined with binocular parallax to produce a dynamic stereoscopic display. This imaging technique is equally applicable to both standard monochrome X-ray imaging and dual-energy X-ray imaging. The latter exploits the difference in magnitude between a high energy X-ray signal and a low energy X-ray signal to compute materials discrimination information made available to the human observer by colour encoding the resultant images. To produce the required image data an integrated dual-energy X-ray camera incorporating a novel castellated dual-energy scintillator arrangement has been developed.

Nuclear materials, especially weapons-grade, can have tremendously adverse consequences in the hands of terrorists. There needs to be a defense in depth to detect and interdict these materials, which should involve some tens of thousands of detectors world-wide. Passive detectors for this purpose have grave sensitivity problems, but these problems are often made worse by avoidable problems of the user interface. Manufacturers need to clearly understand the types of use that their equipment will be put to, the environment in which it will be located, and most especially the personnel who will be using it on a daily basis. International and national field trials have pointed out some problems with user interfaces, and these could best be resolved by manufacturers doing their own testing in simulated environments mimicing that of a customs post or other detector location.

Researchers long have relied on research involving small animals to unravel scientific mysteries in the biological sciences, and to develop new diagnostic and therapeutic techniques in the medical and health sciences. Within the past 2 decades, new techniques have been developed to manipulate the genome of the mouse, allowing the development of transgenic and knockout models of mammalian and human disease, development, and physiology. Traditionally, much biological research involving small animals has relied on the use of invasive methods such as organ harvesting, tissue sampling, and autoradiography during which the animal was sacrificed to perform a single measurement. More recently, imaging techniques have been developed that assess anatomy and physiology in the intact animal, in a way that allows the investigator to follow the progression of disease, or to monitor the response to therapeutic interventions. Imaging techniques that use penetrating radiation at millimeter or submillimeter levels to image small animals include x-ray computed tomography (microCT), single-photon emission computed tomography (microSPECT), and imaging positron emission computed tomography (microPET). MicroCT generates cross-sectional slices which reveal the structure of the object with spatial resolution in the range of 50 to 100 microns. MicroSPECT and microPET are radionuclide imaging techniques in which a radiopharmaceutical is injected into the animal that is accumulated to metabolism, blood flow, bone remodeling, tumor growth, or other biological processes. Both microSPECT and microPET offer spatial resolutions in the range of 1-2 millimeters. However, microPET records annihilation photons produced by a positron-emitting radiopharmaceutical using electronic coincidence, and has a sensitivity approximately two orders of magnitude better than microSPECT, while microSPECT is compatible with gamma-ray emitting radiopharmaceuticals that are less expensive and more readily available than those used with microPET. High-resolution dual-modality imaging systems now are being developed that combine microPET or microSPECT with microCT in a way that facilitates more direct correlation of anatomy and physiology in the same animal. Small animal imaging allows researchers to perform experiments that are not possible with conventional invasive techniques, and thereby are becoming increasingly important tools for discovery of fundamental biological information, and development of new diagnostic and therapeutic techniques in the biomedical sciences.

We are developing a bench-top animal scanner that will acquire both functional SPECT images and anatomical CT images with sub-millimeter spatial resolution for both imaging modalities. This paper presents preliminary results from the evaluation of two x-ray detectors for the CT application, and dual SPECT-CT images using one of these detectors. Two phosphor-CMOS x-ray detectors, one with 48 m pixels and 5 cm x 5 cm area and the other with 50 μm pixels and 12 cm x 12 cm area, were evaluated for linearity and dynamic range. Each detector showed linearity over ~ 3 orders of magnitude, which is sufficient for mouse CT imaging. The smaller detector was mounted to an A-SPECT system, along with a custom 50 W x-ray source with focal spot size of ~ 150 μm. Phantoms and mice were scanned sequentially, SPECT followed by CT, and the resulting reconstructed images fused into a single SPECT-CT image. These preliminary results show that the two detectors evaluated for this application can successfully achieve high contrast CT images of mice and similar sized objects.

A high resolution, hand-held gamma camera has been constructed for use in pre-surgical and intra-operative lymphoscintigraphy. In this paper, we evaluate a compact gamma camera system utilizing NaI(Tl) as a more likely candidate for scintillator due to its greater light yield and faster decay time than CsI(Na) used in an earlier prototype. Using NaI(Tl), the system mean energy resolution is 13% FWHM at 122keV, as compared to 28% in the system with CsI(Na). The highly compact detector head has a 2-cm by 2-cm field of view (FOV) and 1.25-mm intrinsic spatial resolution. Sensitivity of the NaI(Tl) camera was compared with the CsI(Na) camera. At 1cm distance from the tip of collimator, pinhole sensitivity was 58 cps/μCi for the Na(Tl) camera and 37 cps/μCi for the CsI(Na) camera.

This paper discusses display parameters such as display function, contrast, dynamic range, veiling glare and spatial resolution of displays useful in digital radiology. After a review of the traditional display in diagnostic radiology, namely the film-lightbox, based on the film-screen combination, the paper concentrates on the Active Matrix Liquid Crystal Flat Panel Display (AM-LCD). The AM-LCD will most likely mature and may become the display of choice in the near future, replacing the Cathode Ray Tube Display (CRT), which is presently the dominating softcopy display. A comparison between pertinent performance characteristics of AM-LCD and CRT demonstrates that spatial resolution (Modulation Transfer Function or MTF) and veiling glare for the AM-LCD are already superior to those of the CRT.

Bone mineral density (BMD) and body composition estimates are commonly obtained by dual-energy X-ray absorptiometry measurements (DXA). Thanks to their high detection efficiency and good energy resolution at room temperature, semiconductor detectors are more and more utilized to discriminate energy channels for this application. Our purpose is to upgrade the measurements precision using this kind of detector. For a large range of patient morphologies, we simulate X-ray beam transmission measurements with realistic models of tube spectra, and investigate the opportunity offered by spectrometric detectors to cut the signal into n energy channels. By adjusting the channels boundaries, tube voltage and K-edge filtrations, we obtain the best configuration for a given type of patient according to a precision criterion. Furthermore, this configuration is found to be compatible with all the range of patients for BMD measurements. For this configuration, we validate our approach with experimental data acquired with a laboratory made CdZnTe detector.

We have developed a simultaneous CT/SPECT imager using a single Cd_0.9Zn_0.1Te detector in pulse counting mode. Pulse height energy discrimination is used to separate the CT and SPECT data. In pulse counting mode the x-ray flux into the detector must remain below 3 10⁵cps for a linear count rate response. Our SPECT images compare to current clinical systems but our CT images have poor contrast resolution due to the low x-ray flux used to reduce the total photon flux in the detector and pulse pile-up. We are investigating a current mode operation of the detector to obtain high-resolution CT images. Count rate linearity measurements show three orders of magnitude increase in the maximum count rate of the detector and promises to improve the quality of our CT images from the system. Ultimately, interlaced CT/SPECT data could be obtained with no loss in the quality of the SPECT images, and with a significant improvement in the CT images.

Fundamental study on quasi-monochromatic parallel radiography using a polycapillary plate and a plane-focus x-ray tube is described. The x-ray generator consists of a negative high-voltage power supply, a filament (hot cathode) power supply, and an x-ray tube. The negative high-voltage is applied to the cathode electrode, and the transmission type target (anode) is connected to the ground potential. The maximum voltage and current of the power supply were -100 kV (peak value) and 3.0 mA, respectively. In this experiment, the tube voltage was regulated from 20 to 25 kV, and the tube current was regulated by the filament temperature and ranged from 1.0 to 3.0 mA. The exposure time is controlled in order to obtain optimum film density, and the focal spot diameter was about 10 mm. The polycapillary plate is J5022-21 made by Hamamatsu Photonics Inc., and the outside and effective diameters are 87 and 77 mm, respectively. The thickness and the hole diameter of the polycapillary are 1.0 m and 25 μm, respectively. The x-rays from the t ube are formed into parallel beam by the polycapillary, and the radiogram is taken using an industrial x-ray film of Fuji IX 100 without using a screen. In the measurement of image resolution, we employed three brass spacers of 2, 30, and 60 mm in height. By the test chart, the resolution fell according to increases in the spacer height without using a polycapillary. In contrast, the resolution slightly fell with corresponding increases in the height by the polycapillary. In angiography, fine blood vessels of about 100 μm are clearly visible.

The flash x-ray systems developed at the University of Texas at Dallas (UTD) center around two critical subassemblies: (1) a Blumlein pulsed power source, and (2) an x-ray diode properly designed and matched to the pulse forming line. The pulse generator consists of either a single or several traxial Blumleins. For multiple lines, Blumleins are stacked in series at one end and charged in parallel and synchronously commutated with a single switching element at the other end. Extensive characterizations of these Blumlein pulsers have been performed over the past several years. Results indicate that they are capable of producing high power waveforms with risetimes and repetition rates in the range of 0.1-50 ns and 1-300 Hz, respectively, using a conventional thyratron, spark gap, or photoconductive switch. Blumlein pulsers switched by a thyratron or a spark gap have been used to drive x-ray diode loads with different characteristics and discharge geometries and high dose rates of x-rays with pulse durations in the range 3-20 ns have been obtained. In this report the technology and characteristics of these Blumlein based flash x-ray devices are reviewed. Prospects for producing ultra-fast x-ray pulses utilizing photoconductively-switched Blumlein devices are discussed.

The fundamental experiments for measuring soft x-ray characteristics from the vacuum capillary are described. These experiments are primarily performed in order to generate line spectra such as x-ray lasers. The generator consists of a high-voltage power supply, a polarity-inversion ignitron pulse generator, a turbo-molecular pump, and a radiation tube with a capillary. A high-voltage condenser of 0.2 μF in the pulse generator is charged up to 20 kV by the power supply, and the electric charges in the condenser are discharged to the capillary in the tube after closing the ignitron. During the discharge, weakly ionized plasma forms on the inner and outer sides of a capillary. In the present work, the pump evacuates air from the tube with a pressure of about 1 mPa, and a demountable capillary was developed in order to measure x-ray spectra according to changes in the capillary length. In this capillary, the anode (target) and cathode elements can be changed corresponding to the objectives. The capillary diameter is 2.0 mm, and the length is adjusted from 1 to 50 mm. When a capillary with aluminum anode and cathode electrodes was employed, both the cathode voltage and the discharge current almost displayed damp oscillations. The peak values of the voltage and current increased when the charging voltage was increased and their maximum values were -10.8 kV and 4.7 kV, respectively. The x-ray durations observed by a 1.6 μm aluminum filter were less than 30 μs, and we detected the aluminum characteristic x-ray intensity using a 6.8 μm aluminum filter. In the spectrum measurement, two sets of aluminum and titanium electrodes were employed, and we observed multi-line spectra. The line photon energies seldom varied according to changes in teh condenser charging voltage and to changes in the electrode element. In the case where the titanium electrode was employed, the line number decreased with corresponding decreases in the capillary length. Compared with incoherent visible light, these rays from the capillary were diffracted greatly after pass through two slits.

Spectrometers have been developed to record x-ray spectra in the energy range 50 eV to 60 keV. The dispersion elements are transmission crystals for energies higher than approximately 10 keV, reflection crystals for 1 keV to 20 keV, and transmission gratings for energies less than 1 keV. The two-dimensional spectral images are recorded on a CCD or CMOS sensor with a phosphor conversion screen. Silicon photodiodes are positioned in front of the 2D sensor to provide absolute x-ray flux calibrations. The diodes have 1 mm² area and sub-nanosecond time response. The diodes, transmission gratings, and attenuation filters were absolutely calibrated using synchrotron radiation. In addition, the diodes were calibrated in pulsed mode using the soft x-ray (70 eV to 250 eV) pulses from individual electron bunches circulating in the synchrotron storage ring, and a self-calibration model extends the calibration to higher energy. X-ray and extreme ultraviolet spectra were recorded at the OMEGA and NIKE laser facilities. A hard x-ray spectrometer is being built for the National Ignition Facility (NIF) that covers the 1 keV to 20 keV range with one transmission crystal channel and four reflection crystal channels.

Retention and thermal release behavior of hydrogen isotopes in fused silica, synthesized silica and optical fibers were investigated by ion beam analysis technique. Initially contained H in the interior of the specimens is about 0.1~0.2 at.% at room temperature, irrespective of the nominal value of OH concentration. Besides, H atoms more than 1 x 10¹⁶H/cm² was found at the surface. The thermal release of the H atoms from the interior was affected by re-trapping at the near surface. During 5 keV ion injection, the retained D in the implanted layer was quickly saturated with a concentration of about 1 x 10²¹D/cm³. Under the subsequent D injection to doses above 1 x 10¹⁸D/cm², D atoms were trapped with a concentration about 1 at.% in the depth far beyond the projected ranges of D ions. Thermal release of D in the injected layer started at lower temperature than that from the larger depth for lower implantation dose, while the two release curves close to each other for the higher dose. Irradiation of 10 keV He ion into the fused silica caused H up-take in the He implanted depth, where no He atoms were retained.

To promote development of radiation-resistant core optical fibers, the ITER-EDA (International Thermonuclear Experimental Reactor-Engineering Design Activity) recommended carrying out international round-robin irradiation tests of optical fibers to establish a reliable database for their applications in the ITER plasma diagnostics. Ten developed optical fibers were irradiation-tested in a Co-60 gamma cell, a Japan Materials Testing Reactor (JMTR). Also, some of them were irradiation tested in a fast neutron irradiation facility of FNS (Fast Neutron Source), especially to study temperature dependence of neutron-associated irradiation effects. Included were several Japanese fluorine doped fibers and one Japanese standard fiber (purified and undoped silica core), as well as seven Russian fibers. Some of Russian fibers were drawn by Japanese manufactures from Russian made pre-form rods to study effects of manufacturing processes to radiation resistant properties. The present paper will describe behaviors of growth of radiation-induced optical transmission loss in the wavelength range of 350-1750nm. Results indicate that role of displacement damages by fast neutrons are very important in introducing permanent optical transmission loss. Spectra of optical transmission loss in visible range will depend on irradiation temperatures and material parameters of optical fibers.

Fan-beam coherent scatter computer tomography (CSCT) has been employed to obtain 2-dimensional images of spatially resolved diffraction patterns in order to supplement CT images in material discrimination. A Monte Carlo simulation tool DiPhoS (Diagnostic Photon Simulation) was used to create 2-dimensional scatter projection data sets of high-contrast water and Lucite phantom objects with plastic inserts. The results were used as input to a reconstruction routine based on a novel simultaneous iterative reconstruction technique (SIRT). At the same time an experimental demonstrator was assembled to confirm the simulations by measurements and to show the feasibility of coherent scatter CT. It consisted of a 4.5kW constant power X-ray tube, a rotatable object plate and a vertical detector column that could be panned around the object. Spatial resolution was ensured by mechanical collimation. Phantoms similar to those simulated were measured and reconstructed and the contrast achieved by CSCT between the materials under examination substantially exceeded that achieved in CT. A further step was taken by examining an animal tissue sample in the same way, the results of which show remarkable contrast between muscle, cartilage and fat, suggesting that CSCT can also be used in a medical scenario.

Optical transmission properties of optical fibers with a purified and undoped fused-silica core were investigated under irradiation by 14 MeV fast neutrons in the temperature range from room temperature to 573 K at a fast neutron irradiation facility of Fast Neutron Source (FNS). Growth of optical absorption in the wavelength range of 420-630 nm, which includes a well-known absorption peak called Non-Bridging-Oxygen-Hole-Center (NBOHC), took place due to the neutron irradiations. Change of the optical absorption depended strongly on the irradiation temperature. Particularly, growth rate of the radiation-induced optical absorption at the wavelength of 630 nm decreased with increase of the irradiation temperature up to 473 K, because of the dynamic recovery of the initial structural imperfections and the radiation-induced defects.

Strong radioluminescence band and peaks were observed in fused silica core optical fibers under irradiation in fission reactors of Japan Materials Testing Reactor (JMTR) and in gamma-irradiation facility. A broad band in 400-1700 nm could be attributed to Cerenkov radiation, whose intensity was proportional to inverse of the third power of wavelength. The optical intensity of the peak at 450 nm, that was considered to be generated by oxygen vacancies, was proportional to the reactor power under the electronic excitation dose rate up to 5.0 x 10³ Gy/s, and the dynamic range was at least more than five orders of magnitude. The peak intensity depends on details of silica microstructures and became twice after annealing at 773K. By using these radioluminescence peak and band, wide range dosimetry could be actualized in heavy radiation environments.