X-ray devices have demonstrated the ability to characterize a material at the molecular and atomic levels. This ability is particularly important for detecting plastic explosives, where object shape information cannot be used. X-ray devices are relatively inexpensive compared to many other detection technologies. X-ray technology is considered as the technology for detecting illicit materials. Using x-ray technology, a material's <i>density-</i> and <i>effective atomic number</i> or <i>Z_eff</i>-related information can be determined. In theory, an illicit material can be identified using those two pieces of information. This dissertation discusses explosives detection in passenger luggage bags. The x-ray technology used is called <i>R-L</i> multi-sensing technology. The <i>R-L</i> technology was developed by researchers at Virginia Tech. It is the first true multisensing technology used for explosive detection. It uses dual-energy transmission and scatter technologies to obtain characteristic values of an object, i.e., <i>R</i> and <i>L</i>. The material type of this object can then be determined using <i>R-L</i> plane. The characteristic value <i>R</i> is computed using signals from dual-energy transmission modality. <i>R</i> is related to <i>Z_eff</i>. The characteristic value L is computed using signals from low-energy transmission and scatter modalities. <i>L</i> is related to density. Compared to single-sensing technologies and pseudo multi-sensing technologies, the detection accuracy of <i>R-L</i> technology should be much higher. The <i>R</i> and <i>L</i> values of an object can only be computed from an object's <i><b>true</b></i> gray levels. <i><b>True</b></i> gray level refers to the measured gray level of an object when it is not overlapped with any other objects. The problem is objects in a bag almost always overlap with other objects. Being able to identify the object of interest and remove the overlap effects becomes the key issue that needs to be solved. The discussion in this dissertation focuses on the development of the image-processing system used on this multiple sensor system. This image-processing system is comprised of four steps. The first step is to spatially register images from all the sensing modalities. The second step is to remove noise using the edge-preserving smoothing algorithm. The third step is to segment image into regions with relatively uniform gray levels. The fourth step is to compute the true gray levels for objects of interest using the mathematical models for removing overlapping effects. Most of the research focuses on developing a robust segmentation algorithm for segmenting x-ray bag images and developing mathematical models for removing object overlapping effects. The unique contribution of this dissertation includes the development of those mathematical models used for removing object-overlapping effects, and the development of the algorithm for determining an object's true gray levels. The experimental verification shows that the algorithms for registration, smoothing, and segmentation work well. The algorithm that computes the true gray levels of an object can perform the computation quite precisely in transmission modality. However, the methods that were developed for computing an object's true gray levels in scatter images are much less accurate. / Ph. D.

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Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / William L. Dunn / Dense plasma focus (DPF) devices are pulsed power devices capable of producing short-lived, hot and dense plasmas (~10[superscript]19 cm[superscript]-3) through a fast compression of plasma sheath. A DPF device provides intense bursts of electrons and ion beams, X-rays, and 2.5 MeV neutrons when operated with deuterium through the fusion reaction [superscript]2H(d,n)[superscript]3He. The Kansas State University DPF machine was designed and constructed in early 2010. The device was characterized to determine its performance as a neutron source. The device was shown to produce 5.0x10[superscript]7 neutrons/pulse using a tungsten-copper anode. Such machines have the advantages of being non-radioactive, movable, and producing short pulses (typically tens of nanoseconds), which allows rapid interrogation. The signature-based radiation-scanning (SBRS) method has been used to distinguish targets that contain explosives or explosive surrogates from targets that contain materials called “inert,” meaning they are not explosive-like. Different targets were placed in front of the DPF source at a distance of 45 cm. Four BC-418 plastic scintillators were used to measure the direct neutron yield and the neutrons scattered from various targets; the neutron source and the detectors were shielded with layers of lead, stainless steel, and borated polyethylene to shield against the X-rays and neutrons. One of the plastic scintillators was set at 70[supercript]o and two were set at 110[superscript]o from the line of the neutron beam; a bare [superscript]3He tube was used for detecting scattered thermal neutrons. Twelve metal cans of one-gallon each containing four explosive surrogates and eight inert materials were used as targets. Nine materials in five-gallon cans including three explosive surrogates were also used. The SBRS method indicated a capability to distinguish the explosive surrogates in both experiments, although the five gallon targets gave more accurate results. The MCNP code was used to validate the experimental work and to simulate real explosives. The simulations indicated the possibility to use the time of flight (TOF) technique in future experimental work, and were able to distinguish all the real explosives from the inert materials.

Large passive detectors used in screening for special nuclear materials at ports of entry are characterized by poor spectral resolution, making identification of radionuclides a difficult task. Most identification routines, which fit empirical shapes and use derivatives, are impractical in these situations. Here I develop new, physics-based methods to determine the presence of spectral signatures of one or more of a set of isotopes. Gamma-ray counts are modeled as Poisson processes, where the average part is taken to be the model and the difference between the observed gamma-ray counts and the average is considered random noise. In the linear part, the unknown coefficients represent the intensites of the isotopes. Therefore, it is of great interest not to estimate each coefficient, but rather determine if the coefficient is non-zero, corresponding to the presence of the isotope. This thesis provides new selection algorithms, and, since detector data is undoubtedly finite, this unique work emphasizes selection when data is fixed and finite.

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Transportens och logistikens framtid kräver exakta och tillförlitliga men även kostnadseffektiva sensorer. I den här rapporten testas därför några attribut för en Pulse Coherent Radar för att avgöra om det är möjligt att urskilja en person från metall. I rapporten kommer en metod att användas för att skilja de två materialen, detta helt enkelt genom att mäta amplituden av energiinnehållet hos den reflekterade radarstrålen på olika avstånd för de olika materialen. Experimentets resultat visar att metall lätt kan identifieras från en person, men detta endast för att skillnaden i den relativa permittiviteten hos dessa material är väldigt stor. Material med mer likvärdig relativ permittivitet har inte undersökts men mätvärden från dessa material antas vara för likvärdig och därför svårt att identifiera. Metoden anses därför kunna användas då det endast är få material med stor skillnad i relativ permittivitet som ska urskiljas. / The future of transportation and logistics demand accurate and reliable but also cost and energy effective sensors. In this paper, some attribute of a Pulse Coherent Radar will be tested to determine if it is possible to distinguish a person from metal. In the paper one method will be used to distinguish the two materials, this just by simply measure the amplitude of energy of the received radar beam at different distances. Experiment results shows that metal can easily by distinguished from a person, but this only because of the great difference in the relative permittivity of these materials. Experiments for materials with more equivalent relative permittivity have not been investigated. The method is therefore considered to be usable as only a few materials with a large difference in relative permittivity are to be distinguished.