Single sided radiographic imaging would find great utility for medical, aerospace and security applications. While coded apertures can be used to form such an image from backscattered X-rays they suffer from near field limitations that introduce noise. Several theoretical studies have indicated that for an extended source the images signal to noise ratio may be optimised by using a low open fraction (<0.5) mask. However, few experimental results have been published for such low open fraction patterns and details of their formulation are often unavailable or are ambiguous. In this paper we address this process for two types of low open fraction mask, the dilute URA and the Singer set array. For the dilute URA the procedure for producing multiple 2D array patterns from given 1D binary sequences (Barker codes) is explained. Their point spread functions are calculated and their imaging properties are critically reviewed. These results are then compared to those from the Singer set and experimental exposures are presented for both type of pattern; their prospects for near field imaging are discussed.
Many different mask patterns can be used for X-ray backscatter imaging using coded apertures, which can find application in the medical, industrial and security sectors. While some of these patterns may be considered to have a self-supporting structure, this is not the case for some of the most frequently used patterns such as uniformly redundant arrays or any pattern with a high open fraction. This makes mask construction difficult and usually requires a compromise in its design by drilling holes or adopting a no two holes touching version of the original pattern. In this study, this compromise was avoided by 3D printing a support structure that was then filled with a radiopaque material to create the completed mask. The coded masks were manufactured using two different methods, hot cast and cold cast. Hot casting involved casting a bismuth alloy at 80°C into the 3D printed acrylonitrile butadiene styrene mould which produced an absorber with density of 8.6 g cm-3. Cold casting was undertaken at room temperature, when a tungsten/epoxy composite was cast into a 3D printed polylactic acid mould. The cold cast procedure offered a greater density of around 9.6 to 10 g cm-3 and consequently greater X-ray attenuation. It was also found to be much easier to manufacture and more cost effective. A critical review of the manufacturing procedure is presented along with some typical images. In both cases the 3D printing process allowed square apertures to be created avoiding their approximation by circular holes when conventional drilling is used.
The PENELOPE Monte Carlo simulation code was used alongside the SpekCalc code to simulate X-ray energy spectra from a VJ Technologies’ X-ray generator at a range of anode voltages. The PENELOPE code is often utilised in medicine but is here applied to develop coded aperture and pinhole imaging systems for security purposes. The greater computational burden of PENELOPE over SpekCalc is warranted by its greater flexibility and output information. The model was designed using the PENGEOM sub-tool and consists of a tungsten anode and five layers of window materials. The photons generated by a mono-energetic electron beam are collected by a virtual detector placed after the last window layer, and this records the spatial, angular and energy distributions which are then used as the X-ray source for subsequent simulations. The process of storing X-ray outputs and using them as a virtual photon source can then be used efficiently for exploring a range of imaging conditions as the computationally expensive electron interactions in the anode need not be repeated. The modelled spectra were validated with experimentally determined spectra collected with an Amptek X-123 Cadmium Telluride detector placed in front of the source.
The PENELOPE Monte Carlo simulation code was used to determine the optimum thickness and aperture diameter of a pinhole mask for X-ray backscatter imaging in a security application. The mask material needs to be thick enough to absorb most X-rays, and the pinhole must be wide enough for sufficient field of view whilst narrow enough for sufficient image spatial resolution. The model consisted of a fixed geometry test object, various masks with and without pinholes, and a 1040 x 1340 pixels’ area detector inside a lead lined camera housing. The photon energy distribution incident upon masks was flat up to selected energy limits. This artificial source was used to avoid the optimisation being specific to any particular X-ray source technology. The pixelated detector was modelled by digitising the surface area represented by the PENELOPE phase space file and integrating the energies of the photons impacting within each pixel; a MATLAB code was written for this. The image contrast, signal to background ratio, spatial resolution, and collimation effect were calculated at the simulated detector as a function of pinhole diameter and various thicknesses of mask made of tungsten, tungsten/epoxy composite or bismuth alloy. A process of elimination was applied to identify suitable masks for a viable X-ray backscattering security application.
The technique of high-power laser-induced plasma acceleration can be used to generate a variety of diverse effects
including the emission of X-rays, electrons, neutrons, protons and radio-frequency radiation. A compact variable source
of this nature could support a wide range of potential applications including single-sided through-barrier imaging, cargo
and vehicle screening, infrastructure inspection, oncology and structural failure analysis.
This paper presents a verified particle physics simulation which replicates recent results from experiments conducted at
the Central Laser Facility at Rutherford Appleton Laboratory (RAL), Didcot, UK. The RAL experiment demonstrated
the generation of backscattered X-rays from test objects via the bremsstrahlung of an incident electron beam, the electron
beam itself being produced by Laser Wakefield Acceleration.
A key initial objective of the computer simulation was to inform the experimental planning phase on the predicted
magnitude of the backscattered X-rays likely from the test objects. This objective was achieved and the computer
simulation was used to show the viability of the proposed concept (Laser-induced X-ray ‘RADAR’). At the more
advanced stages of the experimental planning phase, the simulation was used to gain critical knowledge of where it
would be technically feasible to locate key diagnostic equipment within the experiment.
The experiment successfully demonstrated the concept of X-ray ‘RADAR’ imaging, achieved by using the accurate
timing information of the backscattered X-rays relative to the ultra-short laser pulse used to generate the electron beam.
By using fast response X-ray detectors it was possible to derive range information for the test objects being scanned. An
X-ray radar ‘image’ (equivalent to a RADAR B-scan slice) was produced by combining individual X-ray temporal
profiles collected at different points along a horizontal distance line scan. The same image formation process was used
to generate images from the modelled data. The simulated images show good agreement with the experimental images
both in terms of the temporal and spatial response of the backscattered X-rays.
The computer model has also been used to simulate scanning over an area to generate a 3D image of the test objects
scanned. Range gating was applied to the simulated 3D data to show how significant signal-to-noise ratio enhancements
could be achieved to resulting 2D images when compared to conventional backscatter X-ray images.
Further predictions have been made using the computer simulation including the energy distribution of the backscatter
X-rays, as well as multi-path and scatter effects not measured in the experiment. Multi-path effects were shown to be the
primary contributor to undesirable image artefacts observed in the simulated images. The computer simulation allowed
the sources of these artefacts to be identified and highlighted the importance of mitigating these effects in the
experiment. These predicted effects could be explored and verified through future experiments.
Additionally the model has provided insight into potential performance limitations of the X-ray RADAR concept and
informed on possible solutions. Further model developments will include simulating a more realistic electron beam
energy distribution and incorporating representative detector characteristics.
This paper reviews landmine neutralisation and marking systems and assesses how they can be down-selected for
incorporation into a technology demonstrator system. The aim will be to illustrate detection, marking and route clearance
capabilities against various anti-tank mines.
A technology comparison matrix has been constructed to allow the down selection of technologies according to defined
criteria. The matrix captures information from a top-level review of a broad range of neutralisation and marking
techniques both currently in use and in development. The methodology allows filtering of technologies using the matrix
and is flexible enough to take into account a range of operational scenarios and requirements. The results of an initial
sub-system down-selection are shown.
The requirements for the final technology down selection with respect to the overall system concepts are discussed. The
application of this technique for down selecting technologies/methods in a broader system context is highlighted.