1. Field of the Invention
The embodiments described herein relate generally to operating security systems and, more particularly, to an x-ray diffraction device and a method for operating a security system having such x-ray diffraction device.
2. Description of Related Art
Many known security systems include an object imaging system that is configured with fan-beam detection technology employing known x-ray diffraction devices. Many of these known fan-beam x-ray diffraction imaging devices include at least one x-ray source to generate a single x-ray fan-beam having multiple photon energies. These screening devices also include a first collimator that facilitates forming the fan-beam. Such devices further include at least one x-ray detector and at least one second collimator that receive at least a portion of a scatter x-ray flux subsequent to interaction of the fan-beam with a piece of the item. The x-ray detector receives at least a portion of the scatter x-ray flux and generates a detector response in the form of a detector signal that is subsequently used to generate an image of the object as discussed further below. These known security systems, wherein such devices are embedded, use coherent x-ray scatter techniques to screen individuals' baggage items with a fan-beam that illuminates a portion of the item, thereby forming an interrogation volume within the item. Such security systems also generate a two-dimensional (2-D) cross-sectional image that facilitates discovery of contraband items and substances.
The fan-beam generated by the device typically illuminates only a portion of a large item and movement of the x-ray source and/or the detector is required to illuminate the entire item and interrogate the entire volume of the item. Moreover, multiple regions separated spatially from one another in the same section of the item must be scanned sequentially as well. Scanning of such items using such known devices requires a finite period of time to scan the entire 2-D cross-section of the item, and thereby illuminate the entire interrogation volume in sequential increments to form a three-dimensional (3-D) image.
Specifically, there may be a large degree of variability in item size and shape that may include irregular surfaces, indentations, and projections, as well as interior and exterior pockets and overlapping contents in the item. Such items will require additional and/or longer scans of these areas, thereby extending a total scan time. Moreover, a spatial resolution of the device, that is, the ability of the device to sharply and clearly define the extent or shape of features within the generated image, varies as a distance between the interrogated volume and the second collimator and detector varies as the collimator and the detector move about the item. Varying such distance tends to vary the properties of the fan-beam, thereby varying the spatial resolution.
In addition, many of such known fan-beam x-ray diffraction imaging devices include components that are arranged and configured to facilitate mechanical movement of either, or all of, the x-ray source, the collimators, and the detector. Such mechanical movement requires motive components that increase the size, weight, and cost of the device. Moreover, such motive components typically require routine inspections, preventative maintenance activities, and occasional corrective maintenance activities. Further, owners will typically maintain a spare parts inventory associated with mechanical movement. The aforementioned activities and spare parts inventories tend to increase a total cost of ownership of the fan-beam x-ray diffraction imaging devices.
Moreover, many known fan-beam x-ray diffraction imaging devices include secondary collimators with symmetrical apertures through which scatter x-rays are transmitted before reaching the detector. Such collimators facilitate cross-talk scattering of x-rays, that is, directing scattered x-rays that propagate through the secondary collimator to combine with desired, or legitimate scattered x-rays to reach the detector and generate false alarms for certain contraband materials and substances. Moreover, such secondary collimators permit only a small proportion of the useful scatter x-ray beam to reach the detector and therefore limit the detector signal. As a consequence of the small detector signal the detection efficiency is impaired. Moreover, an increased number of false alarms are generated. Such false alarms typically require manual inspection of the associated items with the attendant expense of security resources to conduct the inspection and inconvenience to both the owner of the associated items and the security resources. Accordingly, it would be desirable to provide a fan-beam x-ray diffraction imaging device with a method of operation that decreases and/or eliminates movement of the device components and permits the entire useful scatter x-ray beam to reach the detector and inhibits the passage of cross-talk x-rays through the secondary collimator.