Fast neutron radiography scanner for the detection of contraband in air cargo containers

Where are you hiding the pangolins? screening tools to detect illicit contraband at international borders and their adaptability for illegal wildlife trafficking

The illegal movement of wildlife poses a public health, conservation and biosecurity threat, however there are currently minimal screening tools available at international ports of entry to intercept wildlife trafficking efforts. This review first aimed to explore the screening tools available or under development for the detection of concealed wildlife contraband at international ports, including postal services, airlines, road border crossings and maritime routes. Where evidence was deficient, publications detailing the use of methods to uncover other illicit substances, such as narcotics, weapons, human trafficking, explosives, radioactive materials, or special nuclear material, were compiled and assessed for their applicability to the detection of wildlife. The first search identified only four citations related to the detection of wildlife, however the secondary search revealed 145 publications, including 59 journal articles and 86 conference proceedings, describing screening tools for non-wildlife illicit contraband detection. The screening tools uncovered were analysed for potential fitness for purpose for wildlife contraband detection, to evaluate the feasibility of their implementation and their ease of use. The deficiencies evident in terms of resource availability and research efforts targeting wildlife trafficking highlights a potentially substantial national and international security threat which must be addressed.

Elemental analysis of concrete via fast neutron transmission and scattering spectrometry

We report on the development of neutron-based techniques to non-destructively measure the composition of concrete. Previous experimental studies demonstrated the viability of the unfolding technique to determine the ratio of water, sand and cement in well-characterised concrete samples from the transmitted neutron energy spectrum. In this work, we used MCNP6 simulations to demonstrate the extension of the technique to determine elemental compositions from transmitted, or scattered neutron energy spectra. In both cases, the simulated energy spectra provided a reliable method to unfold the composition of samples with known elemental ratios. The precision of the technique was limited by the statistical uncertainties of the simulated spectra, particularly for the case of scattered neutrons. The accuracy of the technique was heavily dependent on the uniqueness of each of the elemental responses, and reasonable prior knowledge of the composition. Given the promising results at this stage, future developments will include the addition of further elements to the response matrix, and experimental verification.

Fast Neutron Scintillator Screens for Neutron Imaging Using a Layered Polymer-Phosphor Architecture

Fast neutrons enable a nondestructive examination of dense, large, and highly attenuating samples due to their lower interaction probability compared to thermal neutrons. However, this also creates a challenge in fast neutron imaging, as the thicker sensors necessary to detect fast neutrons degrade an image’s spatial resolution due to scattering within the sensor and the indeterminate depth of interaction in the sensor. This work explores the advantages of a fast neutron imaging screen with a layered polymer-phosphor screen approach as opposed to a mixed polymer-phosphor screen typically used in fast neutron imaging. Proton recoil is the primary conversion mechanism for fast neutron imaging. Simulations showed that the recoil proton range of typical fast neutrons is approximately 200 µm, however, tests at Idaho National Laboratory revealed that the light output of these screens increased at much greater polymer thicknesses. The NECTAR fast neutron beamline at FRM II was used to test the imaging performance of layered fast neutron imaging screens. Distinguishing between the fast-neutron and γ-ray signals is a major challenge in fast neutron imaging because all fast neutron sources also produce γ-rays. A relative comparison between a control plate and the fast neutron screen was made to distinguish between a γ-ray and fast neutron signals. MCNP modeling quantified the γ-ray and fast neutron contributions to the images measured at NECTAR, which were approximately a 75% γ-ray image.

Hydrogen-Rich 2D Halide Perovskite Scintillators for Fast Neutron Radiography

A fast neutron has strong penetration ability through dense and bulky objects, which makes it an ideal nondestructive technology for detecting voids, cracks, or other defects inside large equipment. However, the lack of effective fast neutron detection materials limits its application. Perovskites have shown excellent optical properties in many areas, but they are absent from fast neutron detection imaging because they cannot directly absorb fast neutrons and emit luminescence. Here, we demonstrate a hydrogen-rich long-chain organic amine modified two-dimensional (2D) perovskite fast neutron scintillator, Mn-(C₁₈H₃₇NH₃)₂PbBr₄(Mn-STA₂PbBr₄). Its hydrogen density can reach 9.51 × 10²⁸ m^-3, and the photoluminescence quantum yield can reach 58.58%, so it is possible to integrate fast neutron absorption and luminescence into a single compound. More importantly, Mn-STA₂PbBr₄ can be made into a large-area self-supporting fast neutron scintillator plate with satisfactory spatial resolution (0.5 lp/mm (lp: line pairs)). This strategy provides a simple and promising choice for fast neutron scintillator nondestructive testing.

Optically Switchable MeV Ion/Electron Accelerator

The versatility of laser accelerators in generating particle beams of various types is often promoted as a key applicative advantage. These multiple types of particles, however, are generated on vastly different irradiation setups, so that switching from one type to another involves substantial mechanical changes. In this letter, we report on a laser-based accelerator that generates beams of either multi-MeV electrons or ions from the same thin-foil irradiation setup. Switching from generation of ions to electrons is achieved by introducing an auxiliary laser pulse, which pre-explodes the foil tens of ns before irradiation by the main pulse. We present an experimental characterization of the emitted beams in terms of energy, charge, divergence, and repeatability, and conclude with several examples of prospective applications for industry and research.

Fast Neutron Imaging with Semiconductor Nanocrystal Scintillators

Fast neutrons offer high penetration capabilities for both light and dense materials due to their comparatively low interaction cross sections, making them ideal for the imaging of large-scale objects such as large fossils or as-built plane turbines, for which X-rays or thermal neutrons do not provide sufficient penetration. However, inefficient fast neutron detection limits widespread application of this technique. Traditional phosphors such as ZnS:Cu embedded in plastics are utilized as scintillators in recoil proton detectors for fast neutron imaging. However, these scintillation plates exhibit significant light scattering due to the plastic-phosphor interface along with long-lived afterglow (on the order of minutes), and therefore alternative solutions are needed to increase the availability of this technique. Here, we utilize colloidal nanocrystals (NCs) in hydrogen-dense solvents for fast neutron imaging through the detection of recoil protons generated by neutron scattering, demonstrating the efficacy of nanomaterials as scintillators in this detection scheme. The light yield, spatial resolution, and neutron-vs-gamma sensitivity of several chalcogenide (CdSe and CuInS₂)-based and perovskite halide-based NCs are determined, with only a short-lived afterglow (below the order of seconds) observed for all of these NCs. FAPbBr₃ NCs exhibit the brightest total light output at 19.3% of the commercial ZnS:Cu(PP) standard, while CsPbBrCl₂:Mn NCs offer the best spatial resolution at ∼2.6 mm. Colloidal NCs showed significantly lower gamma sensitivity than ZnS:Cu; for example, 79% of the FAPbBr₃ light yield results from neutron-induced radioluminescence and hence the neutron-specific light yield of FAPbBr₃ is 30.4% of that of ZnS:Cu(PP). Concentration and thickness-dependent measurements highlight the importance of increasing concentrations and reducing self-absorption, yielding design principles to optimize and foster an era of NC-based scintillators for fast neutron imaging.

The use of MOX caramel fuel mixed with 241Am, 242mAm and 243Am as burnable absorber actinides for the MTR research reactors

The MOX (UO₂&PuO₂) caramel fuel mixed with ²⁴¹Am, ^242mAm and ²⁴³Am as burnable absorber actinides was proposed as a fuel of the MTR-22MW reactor. The MCNP4C code was used to simulate the MTR-22MW reactor and estimate the criticality and the neutronic parameters, and the power peaking factors before and after replacing its original fuel (U₃O₈-Al) by the MOX caramel fuel mixed with ²⁴¹Am, ^242mAm and ²⁴³Am actinides. The obtained results of the criticality, the neutronic parameters, and the power peaking factors for the MOX caramel fuel mixed with ²⁴¹Am, ^242mAm and ²⁴³Am actinides were compared with the same parameters of the U₃O₈-Al original fuel and a maximum difference is -6.18% was found. Additionally, by recycling 2.65% and 2.71% plutonium and ²⁴¹Am, ^242mAm and ²⁴³Am actinides in the MTR-22MW reactor, the level of ²³⁵U enrichment is reduced from 4.48% to 3% and 2.8%, respectively. This also results in the reduction of the ²³⁵U loading by 32.75% and 37.22% for the 2.65%, the 2.71% plutonium and ²⁴¹Am, ^242mAm and ²⁴³Am actinides, respectively.

Conceptual design and optimization of a plastic scintillator array for 2D tomography using a compact D-D fast neutron generator

A conceptual design optimization of a fast neutron tomography system was performed. The system is based on a compact deuterium-deuterium fast neutron generator and an arc-shaped array of individual neutron detectors. The array functions as a position sensitive one-dimensional detector allowing tomographic reconstruction of a two-dimensional cross section of an object up to 10 cm across. Each individual detector is to be optically isolated and consists of a plastic scintillator and a Silicon Photomultiplier for measuring light produced by recoil protons. A deterministic geometry-based model and a series of Monte Carlo simulations were used to optimize the design geometry parameters affecting the reconstructed image resolution. From this, it is expected that with an array of 100 detectors a reconstructed image resolution of ~1.5mm can be obtained. Other simulations were performed in order to optimize the scintillator depth (length along the neutron path) such that the best ratio of direct to scattered neutron counts is achieved. This resulted in a depth of 6-8 cm and an expected detection efficiency of 33-37%. Based on current operational capabilities of a prototype neutron generator being developed at the Paul Scherrer Institute, planned implementation of this detector array design should allow reconstructed tomograms to be obtained with exposure times on the order of a few hours.

A new facility for non-destructive assay using a 252Cf source

A new laboratory facility for non-destructive analysis (NDA) using a time-tagged (252)Cf source is presented. The system is designed to analyze samples having maximum size of about 20 × 25 cm(2), the material recognition being obtained by measuring simultaneously total and energy dependent transmission of neutrons and gamma rays. The equipment technical characteristics and performances of the NDA system are presented, exploring also limits due to the sample thickness. Some recent applications in the field of cultural heritage are presented.

Radiography simulation on single-shot dual-spectrum X-ray for cargo inspection system

We propose a method to identify materials in the dual energy X-ray (DeX) inspection system. This method identifies materials by combining information on the relative proportions T of high-energy and low-energy X-rays transmitted through the material, and the ratio R of the attenuation coefficient of the material when high-energy are used to that when low energy X-rays are used. In Monte Carlo N-Particle Transport Code (MCNPX) simulations using the same geometry as that of the real container inspection system, this T vs. R method successfully identified tissue-equivalent plastic and several metals. In further simulations, the single-shot mode of operating the accelerator led to better distinguishing of materials than the dual-shot system.