Abstract The detection of illicit cargo and hazardous materials within global logistics systems has become a high-security priority due to increasing and diversifying contraband. While modern X-ray and millimeter-wave imaging systems offer excellent throughput and structural visualization for inspection, they face inherent limitations in elemental identification and penetration through high-density cargo. Alternatively, neutron interrogation, which utilizes uncharged particles for inspection, exhibits superior penetration power compared to the other techniques and provides the elemental composition of subject materials through nuclear reactions. This article provides a comprehensive review of neutron-based active interrogation technologies developed over the past three decades for security screening. They are categorized into thermal neutron analysis, pulsed fast neutron analysis, the associated particle technique, and others, based on their physical principles and detectable signatures. Significant research initiatives from the United States, Europe, and Australia are examined, highlighting the transition from laboratory-scale proof-of-concept studies to field-deployable systems. This article discusses technical issues regarding detection sensitivity, inspection times, throughput, and spatial footprint required for radiation safety. Complementary technologies, such as photon interrogation with photoneutrons or nuclear resonance fluorescence, are also reviewed as potential solutions to these constraints. This article presents a perspective on the future evolution of technologies aimed at enhancing the reliability and feasibility of active interrogation in real-world security environments.
Dispersive double reflections realized by means of two bent perfect crystal (BPC) slabs of different cuts used as a sandwich can provide a monochromatic beam of excellent resolution parameters. The dispersive sandwich monochromator/analyzer provides the freedom to combine crystal slabs of different cuts, that is, different crystal reflections for the double diffraction process. For some combination of the individual crystal slab, it is possible to achieve the back-scattering resolution for a rather low monochromator take-off angle. Therefore, by using a suitable combination of two slabs, one can practically obtain a monochromatic neutron beam of any wavelength in the thermal region. Depending on the bending radius of the sandwich the resolution Δλ/λ and the Δ α collimation can be continuously adjusted in the range of 5 × 10 −5 –1 × 10 −3 . Such dispersive BPC elements can also be used for the high-resolution analysis of the scattered beam, as well as for the high-precision λ-calibration of the time-of-flight neutron scattering devices. Another advantage of this dispersive monochromator realization is saving one axis of the neutron scattering instrument.
Accurate calculation of the neutron scattering function for light water from theoretical model is often limited due to the challenges associated with the incoherent and inelastic correction of hydrogen. Traditional correction methods rely on empirical formulas, which lack generality and accuracy. Although quantum correction methods for light water have been studied for a while, they have not yet been translated into practical, openly available tools for calculating the scattering function S ( Q , omega ) . In this paper, we present an open-source computational tool that provides a stable numerical implementation of the Gaussian approximation-assisted quantum correction (GAAQC) framework for light water. The tool applies quantum corrections to classical neutron scattering data derived from molecular dynamics (MD) simulations. It takes two inputs-both obtainable from standard MD trajectories: (a) the vibrational density of states (VDOS) and (b) the classical scattering function S cl ( Q , omega ) -and outputs the quantum-corrected scattering function S ( Q , omega ) . Our implementation overcomes the instabilities that previously limited the GAAQC method, enabling reliable calculation over a wide dynamic range of momentum and energy transfer.
Modern electronic systems are typically highly integrated, structurally complex, and multilayered. During their operational lifecycle, some of these systems inevitably encounter neutron environments, which can lead to their functional failures or equipment damage. To validate their resilience against neutron irradiation, accelerated neutron irradiation tests are generally required. In this study, a multimethod approach was developed to quantify the modulation of the atmospheric neutron beam. Specifically, the neutron modulation induced by multilayered printed circuit boards (PCBs) was measured at the Atmospheric Neutron Irradiation Spectrometer (ANIS) for the first time. Bismuth (Bi) activation foils, a time-of-flight diamond detector, and an static random access memory (SRAM) monitor were used, respectively. The neutron flux decreases by more than 25% for six-layer PCBs across most of the neutron energy range. Monte Carlo simulations were also conducted and compared with the experimental data. This study can help researchers calibrate the experimental results when conducting accelerated neutron irradiation tests at ANIS.
Larmor diffraction (LD) is a neutron scattering technique that offers enhanced resolution by harnessing the Larmor precession of neutron spins in a magnetic field. By encoding subtle changes in neutron momentum transfer into significant alterations in the Larmor phase of neutron spins, LD can be employed to measure lattice expansion, lattice distortion, and mosaicity with exceptional resolution. As originally proposed by Rekveldt et al., LD necessitates the magnetic field boundaries to be tilted to be parallel to the crystal plane of interest. This report explores the fundamental principles shared between LD and spin-echo small-angle neutron scattering (SESANS). Drawing inspiration from the flexibility of SESANS to adjust magnetic field boundaries to optimize the resolution in the measurement of the neutron momentum transfers q , we will demonstrate that the strict requirement of parallel alignment between the magnetic field boundaries and the crystal plane can be relaxed for the measurements of mosaicity. Such relaxation will expand the accessible diffraction angles for these situations that are highly constrained.
