FISSILE MATERIALS DETECTION VIA NEUTRON DIFFERENTIAL DIE-AWAY TECHNIQUE

This work is devoted to the differential die-away technique that is widely used for active detection of fissile materials via pulsed neutron generators. The technique allows direct detection of milligram quantities of uranium-235 and plutonium-239 in objects with volumes up to several cubic meters. Our group has demonstrated this technique, creating a special installation based on the commercially produced ING-07T pulsed neutron generator. The installation includes eight proportional 3 He -counters mounted inside a polyethylene moderator with a cadmium filter, as well as a polyethylene chamber into which a 70-liter container is loaded for inspection. Preliminary testing showed that the minimum detectable mass of unshielded uranium-235 is ∼3 mg, using a 5.108 n/s neutron yield and 8 min measurement time. When the container is filled with neutron absorbing materials, e.g., iron, the minimum detectable mass increases to ∼30 mg. Use of borated screens further increases the minimum mass that can be detected. The tested installation and/or its modifications can be used for control and detection of fissile materials in various applications from luggage inspection to control containers with nuclear fuel cycle radioactive wastes.

A New Image Segmentation Method Based on Improved Fast Implicit Level Set Scheme in X/γ-Ray Inspection System

Digital X/γ-ray imaging technology has been widely used to help people deliver effective and reliable security in airports, train stations, and public buildings. Nowadays, luggage inspection system with digital radiographic/computed tomography (DR/CT) represents a most advanced nondestructive inspection technology in aviation system, which is capable of automatically discerning interesting regions in the luggage objects with CT subsystem. In this paper, we propose a new model for active contours to detect luggage objects in the system, in order to facilitate people to identify the things in luggage. The proposed method is based on techniques of piecewise constant and piecewise smooths Chan-Vese Model, semi-implicit additive operator splitting (AOS) scheme for image segmentation. Different from traditional models, the fast implicit level set scheme (FILS) is ordinary differential equation (ODE). Characterized by no need of any pre-information of topology of images and efficient segmentation of images with complex topology, the FILS scheme is fast more than traditional level set scheme 30 times. At the same time, it performs well in image segmentation of DR images in our experiments.

Cylindrical IEC Fusion Neutron Source for Broad Area NAA

The development of a unique long cylindrical neutron source for broad area neutron activation analysis (NAA) is presented. This source uses inertial electrostatic confinement (IEC) to produce 2.54 MeV D-D or 14.1 MeV D-T fusion neutrons for applications ranging from security inspection stations to driven-subcritical research assemblies. This design uses a biased grid to initial in a unique “star” mode plasma discharge forming beam-background gas (target) fusion. In spherical geometry it routinely produces ∼108 2.54-MeV D-D fusion neutrons/s at steady-state. Pulsed operation has achieved up to 109 neutrons/sec. (equivalent to 1011 n/s using D-T fill). Indeed, a version of the spherical IEC has been produced commercially as a portable neutron source for industrial NAA applications. Recently a cylindrical (2-dimensional version) design based on the spherical unit has been developed. This provides a unique long “line-like” neutron source for use in broad area NAA. This IEC forms ion beams in the volume between the grounded wall and the concentric cylindrical grid. Those beams converge in the center, much like in the star mode spherical IEC. To date, neutron yields of up to 108 D-D neutrons/sec have been achieved with the cylindrical device. A sealed-off unit using getters for gas storage-control has been developed to simplify use in practical applications such as a luggage inspection station. Such units would be filled with deuterium at a central fueling facility, and sent out to the field. After extended operation, they would be returned to this facility for refilling.

Effects of Image Quality, Number of Selectable Viewpoints, and Way to Select the Viewpoint in X-Ray Luggage Inspection

For luggage inspection, a good 3D impression is needed. This impression can be enhanced either by improving the image quality or by providing multiple viewpoints. An experiment is described in which students had to judge whether two objects in a transparent box were connected with a wire. Subjects using head movements to select the viewpoint were compared with subjects using a knob. Viewpoint selection was limited to horizontal movement. The resolution and the number of grey levels of the image as well as the size and the number of discrete steps of image movement were manipulated. Results show that 16 grey levels are sufficient to detect the wire, but that for a correct decision about connectivity, a freedom of movement of at least 90° is desirable. No difference was found between selecting the desired viewpoint with the head and by knob.

A Virtual Design of an Airport Inspection System

Virtual simulations are becoming increasingly important in many areas of engineering and design. Increased computing power is enabling more realistic interactions as well as more complex simulations. A virtual luggage inspection system has been developed incorporating a realistic suitcase model. The models are obtained from several different methods, demonstrating flexibility. Contact detection has been implemented allowing object interaction and manipulation. Force feedback has been integrated, and a force response scheme developed, enabling grasped objects to be felt and evaluated. A fairly robust virtual system capable of handling several applications is presented.