Rapid interrogation of special nuclear materials by combining scattering and transmission nuclear resonance fluorescence spectroscopy

The smuggling of special nuclear materials(SNMs)across national borders is becoming a serious threat to nuclear nonproliferation.This paper presents a feasibility study on the rapid interrogation of concealed SNMs by combining scattering and transmission nuclear resonance fluorescence(s NRF and t NRF)spectroscopy.In s NRF spectroscopy,SNMs such as^(235,238)U are excited by a wide-band photon beam of appropriate energy and exhibit unique NRF signatures.Monte Carlo simulations show that one-dimensional scans can realize isotopic identification of concealed^(235,238)U when the detector array used for interrogation has sufficiently high energy resolution.The simulated isotopic ratio^(235U/238)U is in good agreement with the theoretical value when the SNMs are enclosed in relatively thin iron.This interrogation is followed by t NRF spectroscopy using a narrow-band photon beam with the goal of obtaining tomographic images of the concealed SNMs.The reconstructed image clearly reveals the position of the isotope^(235)U inside an iron rod.It is shown that the interrogation time of s NRF and t NRF spectroscopy is one order of magnitude lower than that when only t NRF spectroscopy is used and results in a missed-detection rate of 10^(-3).The proposed method can also be applied for isotopic imaging of other SNMs such as^(239,240)Pu and^(237)Np.

Editorial: Special subject on the mechanical behavior of thermal protection materials and structures

The thermal protection materials and structures are widely used in hypersonic vehicles for the purpose of thermal insulation, and their mechanical behavior is one of the key issues in design and manufacture of hypersonic vehicles. It is our great pleasure to present the seven papers in this special subject of Theoretical ＆ Applied Mechanics Letters （TAML） and introduce the recent progresses on the mechanical behavior of thermal protection materials and structures by the authors.

Guest Editorial——TTA Special Section on Terahertz Materials and Devices

Lying between radio frequency and infrared radiation, terahertz （THz） wave encounters lots of difficulties to produce, detect, transmit, and modulate. Great efforts have been made to construct THz devices, including sources, detectors, switches, modulators, lenses, and filters. However, only moderate progresses have been made in THz generation and detection. Furthermore, the devices and techniques to control and manipulate THz waves are still in its infancy. Therefore, it is still a challenge to date to develop sophisticated THz application systems such as communication, sensing, safety inspection, imaging and medical diagnose systems. This difficult position of THz wave is essential due to the deficiency of THz materials having a suitable THz electromagnetic response, as compared to its neighboring microwave and infrared regime. Practicable material will largely push the THz technology to real-world applications. The GaAs/AlxGa~_xAs material system, for example, is the heart of THz quantum cascade lasers. High quality NbN films, again, set the basis of THz hot electron bolometer.

Preface to Special Issue on Carbon Materials for Energy Application

The rising cost and limited availability of fossil fuels, and the increasing concerns related to their role on global pollution and greenhouse effect have pushed considerably the need to accelerate the transition to a more sustainable use of energy based largely on renewable energy sources. Nanocarbon materials play a critical role in this transition, as they are the key materials for components of different devices necessary in enabling this transition （batteries, fuel cells, solar cells, etc.）. This issue collects 22 contributions, including one perspective and six review papers on the topic of carbon materials for energy applications, written by well-known experts in this field. It is really an exciting special issue that gives a very updated view of this topic, as well as trends and outlooks in this breakthrough research area. The initial perspective paper introduces the different possibilities offered from the growing level of knowledge in this area, testified from the exponentially rising number of publications. It also discusses the basie concepts for a rational design of these nanomaterials. The lk）llowing six reviews address different specific aspects of synthesis, characterization and use of carbon nanomaterials, from fuel cells to composite electrodes, supercapacitors and photoelectrochemical devices for CO2 conversion. These reviews represent an unique opportunity for the readers to be updated on the latest developments of new carbon families such as fullerene, grapbene, and carbon nanotube, and their derived nanocarbon materials （from carbon quantum dots to nanohorn, nanofiber, nano ribbon, etc.）. Second generation nanocarbons, including modification of these nanocarbons by surface functionalization or doping with heteroatoms to create specific tailored properties, and nanoarchitectured supramolecular hybrids, are also discussed. Finally, 1 communication and 14 full articles discuss several aspects of the use of these nanocarbon materials to develop new catalysts for a range of applications （from biomass conversion to Fisher-Tropsch reaction and electrochemical devices） and new materials for energy storage and conversion （adsorption pumps, Li-ion and Li-S batteries, electrodes for electrochemical uses）. We thus believe that this special issue dedicated to the use and development of carbon materials for energy applications represents a unique occasion for young and experienced researchers as well as for managers in the field of sustainable energy to have an updated view on this enabling topic for the future of our society. We thus invite all to have this special issue as a privileged component of your bookshelf.

Special Issue on New Concepts and Advances in Photocatalytic Materials for Sustainable Energy

The use of solar energy to drive the chemical and energy processes,and the chemical storage of solar energy are the key elements to move to a low-carbon economy,sustainable society and to foster energy transition.For this reason,there is a fast-growing scientific interest on this subject,which is part of the general effort for a solar-driven chemistry and energy,the chemistry of the future.To realize this

Optical spectroscopy and crystal-field strength of Cr^(3+) in various solid matrixes

The Cr^3＋：BeAl2O4 crystal, Cr^3＋：LiNbO3 crystal, and ZnO-Al2O3-SiO2 glass-ceramic were obtained by the Czochralski technique, Bridgman method, and melting processing, respectively. The optical absorption and emission spectra of the above Cr^3＋-incorporated solid-state materials were recorded. The technical parameters for growing high-quality Cr^3＋：BeAl2O4 and Cr^3＋：LINbO3 crystals were obtained. The results indicate that the optical absorption and fluorescence spectra of Cr^3＋ show quite a few differences in various matrixes. The sharp line emissions were observed in the Cr^3＋：BeAl2O4 and Cr^3＋：LiNbO3 crystals. The crystal-field parameters （Dq） for Cr^3＋. in different matrixes were calculated from their corresponding spectra. It is indicated that Cr^3＋：BeAl2O4 and Cr^3＋：LiNbO3 belong to the high-field site crystal, while the Cr^3＋ ZnO-Al2O3-SiO2 glass and glass-ceramic belong to the weak-field site crystal.

Hydrothermal Synthesis of Nanostructural La_xBi_(2-x)Se_yTe_(3-y) Powders

Nanostructural monophase LaxBi2-xSeyTe3-y alloy was synthesized with a hydrothermal route using BiCl3, LaCl3, selenium and tellurium powders as the precursors, NaOH and disodium ethylenediaminetetraacetiate （EDTA） as the additives. The hydrothermally synthesized powders have a petal-like morphology self-structured by the parallel side-by-side arrangement of the nano-scales. It is found that an alkaline additive is necessary for the synthesis of a monophase Bi2Te3 based alloy.

Editorial for rare metals, special issue on advanced thermoelectric materials

As a clean energy technology to combat the global energy dilemma and the environmental problems, thermoelectrics that enable a direct conversion between heat and electricity have attracted increasing attention in recent decades. This solid-state, vibrationless technology has long been used for powering the spacecrafts of several deep-space missions and has limited commercial use in niche market, but these are now actively considered for a variety of new applications, such as the conversion of automobile exhaust heat into electricity. Meanwhile, materials research flourishes with the knowledge that significantly improves the thermoelectric efficiency for even more applications. This motivates Rare Metals to have a special issue focusing on thermoelectrics.

Preface to the Special Issue on Si-Based Materials and Devices

It has been well known that the development of microelectronic and integrated circuit （IC）, mainly based on silicon materials, have changed the way of our life dramatically and accelerated the development and innovation of new technologies. With the increase of integration density in ICs, the gate lengths of transistors are now scaled down to 7 nm, leading to fundamental challenges to keep up with the Moore＇s law. One possible solution is to integrate optical circuits into the Si microelectronic platform to achieve high density electronic-photonic integration.

Virtual special issue:Organic and polymer materials for electronics

Welcome to this virtual special issue focusing on organic and polymer materials for electronics published in Chinese Chemical Letters since 2017. For more than a century, people have always believed that organic compounds cannot be well employed for electronic conducting. Till 2000,Heeger,MacDiarmid and Shirakawa were acknowledged by the Nobel Prize of chemistry for

Editorial for special issue on photonics based on two-dimensional noncarbon materials

Scientists are in the constant search of novel materials,or innovative applications of existing materials to solve problems we face in our everyday life.Although graphene,the two-dimensional（2D）form of carbon,has been a star player for the past decade,there is a significant shift towards other noncarbon materials in recent years.Apart from the large family of transition metal dichalcogenides（TMDs）,mono-elemental materials,such as phosphorene,arsenene,antimonene.