Halide lead perovskites have attracted increasing attention in recent years for ionizing radiation detection due to their strong stopping power, defect-tolerance, large mobility-lifetime (μτ) product, tunable bandgap and simple single crystal growth from low-cost solution processes. In this review, we start with the requirement of material properties for high performance ionizing radiation detection based on direct detection mechanisms for applications in X-ray imaging and γ-ray energy spectroscopy. By comparing the performances of halide perovskites radiation detectors with current state-of-the-art ionizing radiation detectors, we show the promising features and challenges of halide perovskites as promising radiation detectors.

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Halide lead perovskites for ionizing radiation detection

Laser-wakefield accelerators (LWFAs) were proposed more than three decades ago, and while they promise to deliver compact, high energy particle accelerators, they will also provide the scientific community with novel light sources. In a LWFA, where an intense laser pulse focused onto a plasma forms an electromagnetic wave in its wake, electrons can be trapped and are now routinely accelerated to GeV energies. From terahertz radiation to gamma-rays, this article reviews light sources from relativistic electrons produced by LWFAs, and discusses their potential applications. Betatron motion, Compton scattering and undulators respectively produce x-rays or gamma-rays by oscillating relativistic electrons in the wakefield behind the laser pulse, a counter-propagating laser field, or a magnetic undulator. Other LWFA-based light sources include bremsstrahlung and terahertz radiation. We first evaluate the performance of each of these light sources, and compare them with more conventional approaches, including radio frequency accelerators or other laser-driven sources. We have then identified applications, which we discuss in details, in a broad range of fields: medical and biological applications, military, defense and industrial applications, and condensed matter and high energy density science.

/pdf/applications-of-laser-wakefield-accelerator-based-light-1ahbhzp8lh.pdf

Applications of laser wakefield accelerator-based light sources

Summary Metal halide perovskites (MHP) have demonstrated excellent X-ray detection performance, thanks to their compelling properties including large mobility-lifetime product, strong X-ray absorption, and easy synthesis, etc. The latest progress and future perspective of MHP-based X-ray detection and imaging are reviewed herein. The fundamental knowledge of X-ray interaction with materials and the characteristics of direct and indirect (via scintillators) X-ray detection is first discussed. We then introduce the methods for scalable fabrication of MHP and summarize their recent device performance. We further present the integration of MHP detectors with readout integrated circuits and the associated performance metrics for flat panel detector (FPD). We also briefly talk about ways to minimize cross-talk and increase spatial resolution in FPDs. Last, we provide some cautions to evaluate the detector performance and some suggestions to further improve the performance. We hope this paper can help readers understand the status and future challenges for perovskite X-ray detectors.

Metal Halide Perovskites for X-Ray Detection and Imaging

X-ray screening systems have been used to safeguard environments in which access control is of paramount importance. Security checkpoints have been placed at the entrances to many public places to detect prohibited items, such as handguns and explosives. Generally, human operators are in charge of these tasks as automated recognition in baggage inspection is still far from perfect. Research and development on X-ray testing is, however, exploring new approaches based on computer vision that can be used to aid human operators. This paper attempts to make a contribution to the field of object recognition in X-ray testing by evaluating different computer vision strategies that have been proposed in the last years. We tested ten approaches. They are based on bag of words, sparse representations, deep learning, and classic pattern recognition schemes among others. For each method, we: 1) present a brief explanation; 2) show experimental results on the same database; and 3) provide concluding remarks discussing pros and cons of each method. In order to make fair comparisons, we define a common experimental protocol based on training, validation, and testing data (selected from the public ${\mathbb {GDX}}$ ray database). The effectiveness of each method was tested in the recognition of three different threat objects: 1) handguns; 2) shuriken (ninja stars); and 3) razor blades. In our experiments, the highest recognition rate was achieved by methods based on visual vocabularies and deep features with more than 95% of accuracy. We strongly believe that it is possible to design an automated aid for the human inspection task using these computer vision algorithms.

Modern Computer Vision Techniques for X-Ray Testing in Baggage Inspection

https://pure.rug.nl/ws/files/134440967/1_s2.0_S0010854520302411_main.pdf

Modern X-ray spectroscopy: XAS and XES in the laboratory

Since 9/11, there has been a growing interest to improve the security both of air travel and of cargo shipping. Visual inspection is the simplest tool and is very efficient when single objects of small size are to be checked. The complexity of inspection increases when we have large 'boxes' and/or when several objects are packed into a closed space, as in luggage or even in larger volumes like shipping containers or trucks. This paper gives a brief overview of how different X-ray techniques are used for fast checking of small and large objects.

X-ray imaging for homeland security

Since 9/11 there has been a growing interest to improve the security both of air travel and of cargo shipping. Visual inspection is the simplest tool and is very efficient, when single objects of small size are to be checked. The complexity of inspection increases as we have large "boxes" and when several objects are packed into a closed space, such as in a luggage or even in larger volumes like shipping containers or trucks. An obvious method to check these objects is using X-rays, which can penetrate through the shipping "boxes" and let us see what is inside. It is well known that the X-ray absorption of an object depends on the absorption coefficient and the thickness of a given material. So X-ray is an excellent tool to check luggage without opening and manually checking each of them. This paper gives an overview of different x-ray luggage inspection techniques from simple transmission imaging to multi-energy and 3D X-ray computer tomography (CT). However, none of the X-ray imaging methods give a full differentiation between a plastic explosive and a bag of flour of the same shape. X-ray diffraction is a more sophisticated method to differentiate materials with and without crystalline structure and among materials of different crystalline structures. There is also a real danger that not only traditional explosives but nuclear materials can be smuggled into the US in cargo containers and trucks. Not only the explosion of a nuclear bomb but also a so called "dirty bomb" could cause death and panic in large cities. So to check the containers before they enter the country, for explosives and especially for nuclear materials is a primary goal. As it was mentioned earlier the X-ray absorption of the materials depends on the X-ray energy. Higher energy mega-electronvolt X-rays can penetrate through thick steels and other highly absorbent materials. This makes it possible to check the content of shipping containers or trucks with steel walls in the loading area. The theory and limits of high energy X-ray imaging, dual energy X-ray imaging, and high energy CT are also demonstrated. A further application using X-rays is back scatter imaging. This technique is especially useful for detection of landmines and IEDs (Improvised Explosive Devices) as it will be shown below. Finally, the use of neutron detection for identifying nuclear materials will be mentioned. Neutron detection is a viable alternative to X-ray imaging for finding nuclear materials.

George Zentai

Papers

X-ray imaging for homeland security

X-ray imaging for homeland security