14 research outputs found
Detectors for the Gamma-Ray Resonant Absorption (GRA) Method of Explosives Detection in Cargo: A Comparative Study
Gamma-Ray Resonant Absorption (GRA) is an automatic-decision radiographic
screening technique that combines high radiation penetration with very good
sensitivity and specificity to nitrogenous explosives. The method is
particularly well-suited to inspection of large, massive objects (since the
incident gamma-ray probe is at 9.17 MeV) such as aviation and marine
containers, heavy vehicles and railroad cars. Two kinds of gamma-ray detectors
have been employed to date in GRA systems: 1) Resonant-response nitrogen-rich
liquid scintillators and 2) BGO detectors. This paper analyses and compares the
response of these detector-types to the resonant radiation, in terms of
single-pixel figures of merit. The latter are sensitive not only to detector
response, but also to accelerator-beam quality, via the properties of the
nuclear reaction that produces the resonant gamma-rays. Generally, resonant
detectors give rise to much higher nitrogen-contrast sensitivity in the
radiographic image than their non-resonant detector counterparts and
furthermore, do not require proton beams of high energy-resolution. By
comparison, the non-resonant detectors have higher gamma-detection efficiency,
but their contrast sensitivity is very sensitive to the quality of the
accelerator beam. Implications of these detector/accelerator characteristics
for eventual GRA field systems are discussed.Comment: 11 page
Low-Dimensional Organic-Inorganic Halide Perovskite: Structure, Properties, and Applications
Three-dimensional (3âD) perovskite has attracted a lot of attention owing to its success in photovoltaic (PV) solar cells. However, one of its major crucial issues lies in its stability, which has limited its commercialization. An important property of organic-inorganic perovskite is the possibility of forming a layered material by using long organic cations that do not fit into the octahedral cage. These long organic cations act as a "barrier" that "caps" 3âD perovskite to form the layered material. Controlling the number of perovskite layers could provide a confined structure with chemical and physical properties that are different from those of 3âD perovskite. This opens up a whole new batch of interesting materials with huge potential for optoelectronic applications. This Minireview presents the synthesis, properties, and structural orientation of low-dimensional perovskite. It also discusses the progress of low-dimensional perovskite in PV solar cells, which, to date, have performance comparable to that of 3âD perovskite but with enhanced stability. Finally, the use of low-dimensional perovskite in light-emitting diodes (LEDs) and photodetectors is discussed. The low-dimensional perovskites are promising candidates for LED devices, mainly because of their high radiative recombination as a result of the confined low-dimensional quantum well
Multidimensional perovskites : a mixed cation approach towards ambient stable and tunable perovskite photovoltaics
Although halide perovskites are able to deliver high power conversion efficiencies, their ambient stability still remains an obstacle for commercialization. Thus, promoting the ambient stability of perovskites has become a key research focus. In this review, we highlight the sources of instability in conventional 3âD perovskites, including water intercalation, ion migration, and thermal decomposition. Recently, the multidimensional perovskites approach has become one of the most promising strategies to enhance the stability of perovskites. As compared to pure 2âD perovskites, multidimensional perovskites typically possess more ideal band gaps, better charge transport, and lower exciton binding energy, which are essential for photovoltaic applications. The larger organic cations in multidimensional perovskites could also be more chemically stable at higher temperatures than the commonly used methylammonium cation. By combining 3âD and 2âD perovskites to form multidimensional perovskites, halide perovskite photovoltaics can attain both high efficiency and increased stability.NRF (Natl Research Foundation, Sâpore)ASTAR (Agency for Sci., Tech. and Research, Sâpore)MOE (Min. of Education, Sâpore)Accepted versio