Esam M.A. Hussein

Landmine detection: the problem and the challenge.

This paper explores the role of radiation methods in addressing the problem of detecting landmines. The application of neutron activation analysis, with an isotopic source or a pulsed neutron generator, is discussed. The use of neutron moderation as an indicator of the presence of a landmine is also explored. In addition, information provided by measuring scattered photons (gamma- and X-rays) is examined.

Review of one-side approaches to radiographic imaging for detection of explosives and narcotics

There are occasions, in the course of determining if an explosive threat exists, where access to both sides of an article to be interrogated is not possible, as in the detection of landmines or the inspection of baggage left unattended and abutted against a wall. In such cases, a one-side approach to imaging must be undertaken. This paper reviews existing approaches to radiological imaging and assesses their potential application to the detection of explosives and narcotics.

A compton scattering method for inspecting concrete structures

Abstract The feasibility of a Compton scattering technique for the inspection of extended concrete structures for the presence of steel rebar and void enclosures is demonstrated experimentally and by Monte Carlo simulations. A parametric study is performed which identifies the source energy and Compton scattering angle as the most dominant variables affecting the technique. A simple optimization method is, subsequently, developed to aid in the determination of the most appropriate source-detector arrangement for a given depth of concrete.

Three dimensional imaging of porosity and tracer concentration distributions in a dolostone sample during diffusion experiments using X-ray micro-CT.

X-ray micro-computed tomography (micro-CT) techniques for measuring the three-dimensional (3-D) distributions of diffusion-accessible porosity (φ(d)) and temporal tracer-concentrations (C(t)) within a dolostone sample subjected to solute diffusion are developed and tested in this work. The φ(d) and C(t) measurements are based on spatially resolved changes in X-ray attenuation coefficients in sequentially acquired 3-D micro-CT datasets using two (calibration and relative) analytical approaches. The measured changes in X-ray attenuation coefficient values are a function of the mass of X-ray absorbing potassium-iodide tracer present in voxels. Mean φ(d) values of 3.8% and 6.5% were obtained with the calibration and the relative approaches, respectively. The detection limits for φ(d) measurements at individual voxel locations are 20% and 36% with the calibration and the relative methods, respectively. The detection limit for C(t) are 0.12 M and 0.22 M with the calibration and the relative approaches, respectively. Results from the calibration method are affected by a beam-hardening artifact and although results from the relative approach are not affected by the artifact, they are subject to high detection limits. This work presents a quantitative assessment of micro-CT data for studies of solute transport. Despite limitations in precision and accuracy, the method provides quantitative 3-D distributions of φ(d) and C(t) that reflect solute diffusion in heterogeneous porous geologic media.

A 252CF NEUTRON TRANSMISSION TECHNIQUE FOR BULK DETECTION OF EXPLOSIVES

Abstract A 252 Cf fast-neutron transmission method for bulk detection of nitrogen-rich explosives, concealed in passenger luggage, is presented. The technique utilizes the cross-section resonances of two elements dominant in explosives (nitrogen and oxygen). These resonances are portrayed in the pulse-height distribution of transmitted neutrons measured with a helium-3 detector. Monte Carlo simulations are used to support the theoretical concept of the method. The feasibility of the technique is demonstrated in the laboratory employing an explosive-like material (nitrogen-rich fertilizer).

Detection of debonding in composite-aluminum joints using gamma-ray Compton scattering

Abstract Gamma-ray Compton scattering is used for the detection of debonding in adhesively bonded composite-aluminum joints. A collimated narrow beam of monochromatic photons, generated by a 137 CS source, is directed towards the joint and scattered photons are recorded, using a detector located on the same side as the source. The energy of the scattered radiation is measured and related to the angle of scattering. The occurrence of debonding is indicated by a change in the count rate at an energy corresponding to its location. The performance of the technique is successfully demonstrated experimentally for joints of different adhesive-bonding thicknesses and for artificially induced debonds.

A compton-scatter spectrometry technique for flaw detection

The energy spectrum of Compton scattered photons is used for detecting collinear flaws and defects in laminated or composite materials. By relating the energy of scattered photons to their angle of scattering, indications of material density at different locations along the beam path are obtained. The difficulty of utilizing a detector of finite size to obtain point-to-point scattering information is overcome by viewing the physical detector as being composed of a number of virtual point detectors. The paper presents the results of tests of this technique, using a 60Co collimated photon beam for detecting small collinear defects in aluminum blocks and in laminated composite materials. The tests show that flaws as small as 0.5 mm in size are visible in the scattering spectrum.

Design aspects of a gamma-ray energy-spectral Compton-scatter nondestructive testing method

Abstract Methods for resolving the direction of scattering from the gamma-ray energy spectrum in Compton-scatter nondestructive testing are examined. With good source collimation and a well-confined detectors field-of-view, it is shown that scattering angles can be directly determined from the energy-calibrated pulse-height distribution, without numerical unfolding. Factors affecting this process are studied and system-design guidelines are outlined. The application of the technique for the detection of multiple collinear flaws, as well as to inspect a multilayered structure, is successfully demonstrated.

Algorithms for density and composition-discrimination imaging for fourth-generation CT systems.

This paper shows that if the off-beam idle detectors in the detection ring of a fourth-generation x-ray computed tomography (CT) system are used to measure the scattered radiation, it is numerically feasible to reconstruct electron-density images to supplement the conventional attenuation-coefficient images of transmitted radiation. It is also shown that by combining these two images, composition changes can be detected with the aid of an effective-atomic-number indicator. The required image-reconstruction algorithms are developed and tested against Monte Carlo simulated measurements, for a variety of phantom configurations. In spite of the relatively poor statistical quality of scattering measurements, it is demonstrated that electron-density images of reasonable quality can be obtained. In addition, it is shown that composition discrimination is possible for materials of effective atomic number greater than five, in the photon energy range of a typical medical x-ray CT system operating at 102 kVp. The obtained supplementary electron-density and composition images can be useful in radiotherapy planning and for studying tumour histology, as well as in industrial and security applications where identification of materials based on density and composition is important.

An empirical fast-neutron technique for detection of explosive-like materials

Abstract A method for detecting explosives in airport baggage using fast-neutron scattering and transmission measurements is presented. Ammonium nitrate (a commercial fertilizer) is used in the laboratory to simulate an explosive-like substance. The measurements are combined in Cartesian maps of normalized pairs of measurements. The existence of fertilizer manifests itself in these maps within a distinct region which is not significantly altered by the presence of surrounding materials. Monte Carlo simulations further confirm this phenomenon.