Re-emission Processes Research Articles

Analysis of signal waveform from a midsize liquid argon detector

The midsize single-phase liquid argon prototype detector, operating at the surface laboratory, is designed to measure scintillation light emitted by the liquid argon (LAr). The detector employs 42 8-inch photomultiplier tubes (PMT) to collect the light. By analyzing the waveform of the signal, important detector characteristics such as the slow decay time constant that characterizes the purity of the liquid argon can be obtained. To describe the signal waveform, a model, which takes into account the liquid argon emission decay times together with the TPB re-emission process as well as the signal reflection effects, is used. The TPB re-emission process is introduced using a three-exponential time structure. Additionally, experimental results provide comprehensive validation for a post-peak hump structure, which is attributed to signal reflection.

New and legacy pesticidal persistent organic pollutants in the agricultural region of the Sultanate of Oman

Comprehensive air and surface soil monitoring was conducted for new and legacy organochlorine pesticides (OCPs) to fill the knowledge and data gap on the sources and fate of pesticidal persistent organic pollutants (POPs) in the Sultanate of Oman. DDTs in agricultural soil samples ranged from 0.013 to 95.80 ng/g (mean: 8.4 ± 25.06 ng/g), with a median value of 0.07 ng/g. The highest concentration was observed at Shinas, where intensive agricultural practice is prevalent. The dominance of p,p′-DDT in soil and air reflected technical DDT formulation usage in Oman. Among newly enlisted POPs, pentachlorobenzene had the maximum detection frequency in air (47%) and soil (41%). Over 90% of sites reflected extensive past use of hexachlorobenzene. Major OCP isomers and metabolites showed net volatilisation from the agricultural soil, thereby indicating concurrent emission and re-emission processes from the soil of Oman. However, the cleansing effect of oceanic air mass is the possible reason for relatively lower atmospheric OCP levels from a previous study. Although DDT displayed maximum cancer risk, the level is below the permissible limit. DDT primarily stemmed from obsolete stock and inadequate management practices. Hence, we suggest there is a need for DDT regulation in Oman.

Contaminant sorption on soil and indoor materials and its possible impact on transients in vapor intrusion – An example based upon trichloroethylene (TCE)

Although building materials are well recognized as potential sources and sinks of indoor volatile organic compounds (VOCs), knowledge about how they affect indoor air concentrations and measurements in vapor intrusion scenarios is limited. This study investigates the potential influence of sorption processes on indoor air contamination in vapor intrusion, relying upon laboratory measurements at relevant concentration levels, and applying these in a numerical transient vapor intrusion model. It was found that the sink effect of adsorption on building materials can lower indoor air concentrations or delay their achieving a steady state, thus cautioning that these processes can affect observed indoor air concentration variability. Building materials can also serve as secondary sources of pollutants in vapor intrusion mitigation scenarios, which might affect the evaluation of the efficiency of mitigation efforts. For example, it was predicted that in a cinderblock structure it could take up to 305 h to reduce indoor trichloroethylene (TCE) concentrations by 50 % due to the re-emission of TCE from the cinderblock, whereas it would take only 1.4 h without the re-emission process.

Влияние дополнительных монопольных выбросов электронов на зарядовые спектры конечных ионов при каскадном распаде электронных вакансий в атоме золота

The probabilities of the formation of final ions produced by the cascade decays of vacancies in the K, L, M, N, and O shells of the gold atom are calculated. Simulation of the cascade decays of vacancies is performed by direct construction and analysis of decay trees using branching ratios and transition energies calculated in the Pauli–Fock approximation for multivacancy electron configurations arising in the course of the cascade decay. Accounting for additional monopole ejections of electrons (shake-off) accompanying the cascade transitions leads to a slight increase in the average charges of the final ions, by 0.15–0.23e. The largest relative increase in the calculated average charges of the final ions (by 3.6–3.9%) is observed upon the cascade decay of vacancies in 4p3/2, 4d3/2, and 4d5/2 subshells, and the smallest (by 0.8%) occurs in the decay of 4f-vacancy. Despite insignificant changes in the average ion charges, the structure of the charge spectra in some cases changes noticeably enough when additional electron ejections are taken into account. It is expected that in simulation of the cascade energy reemission processes when heavy atoms are used as radiosensitizers, the effect of accounting for shake-off processes will be insignificant.

Dual sites design of CoFe/Mg MMO catalyst for effectively suppressing dimethylamine re-emission: Degradation products and DFT calculation

Dimethylamine (DMA), a widely used organic solvent and famous malodorous volatile organic compound (VOC), is easily released into the atmosphere and harms human health. Here, we designed a bifunctional CoFe/Mg mixed metal oxide (MMO) catalyst for activating peroxymonosulfate (PMS) to degrade aqueous DMA, thereby inhibiting DMA re-emission. The results indicated that the DMA (100 mg/L) degradation efficiency exceeded 90% within 80 min. Moreover, the re-emission of DMA into the atmospheric environment was reduced by 80% after catalysis. Electron paramagnetic resonance (EPR) measurements and quenching tests verified SO4•− and •OH as the active oxygen species in the CoFe/Mg MMO–PMS system. Combined characterization and density functional theory (DFT) calculation results confirmed that the Co species served as catalytic sites for PMS activation, and the adjacent Mg species acted as adsorption sites for DMA. The synergy effects between the dual sites could accelerate the PMS activation, facilitate the generation of free radicals, and shorten the migration distance between free radicals and pollutants, to realize the efficient DMA degradation. The degradation mechanism and suppressing re-emission process were proposed. This study will provide distinctive insights into the design of catalysts with dual sites and pioneer an unparalleled approach to the industrial governance of effluvial VOCs treatment.

Impact of photon recycling on the light extraction from metal halide perovskite light emitting diodes

The impact of photon recycling on the efficiency of light extraction from metal halide perovskite light emitting diodes is quantified using a novel modelling framework based on a detailed-balance compatible Green dyad approach. Analysis of photon modes contributing to internal emission and iterative evaluation of re-absorption and re-emission processes is performed for single perovskite layers in absence and presence of a metallic reflector and under consideration of associated parasitic absorption losses. Finally, the approach is employed to characterize the emission characteristics of a realistic multilayer device stack in dependence of the emitter thickness.

Теоретическое исследование влияния рассеивающей среды, состоящей из атомов калия, на время затухания люминесцентного сигнала с использованием метода Монте-Карло

The study solves the problem of the luminescent photons propagation in a resonantly absorbing medium consisting of atoms of the studied substance and a buffer inert gas. The Monte Carlo method was used in numerical experiments carried out to simulate real processes that occur in a chamber designed to determine the lifetime of an individual atom in an excited state by the method of measuring the luminescence intensity decay time. Findings of the research show that when luminescent photons are repeatedly scattered (scattering means the process of absorption and re-emission of a photon by an atom) in a medium, the luminescence decay time noticeably increases, reaching a value greater than the average lifetime of an individual atom in an excited state. The reflection of photons from the walls that make up the chamber can lead to errors in measuring the lifetime. The process of luminescence decay is studied theoretically for various detunings of the laser frequency from the resonant transition frequency. A three-level model of the atom and a model of complete frequency redistribution were applied. The study describes an algorithm based on the Monte Carlo method, which is used to model the three-level population kinetics, laser radiation transfer, radiation trapping, and frequency redistribution

Characterization of atmospheric total gaseous mercury at a remote high-elevation site (Col Margherita Observatory, 2543 m a.s.l.) in the Italian Alps

The Col Margherita (MRG) Observatory is a high-altitude background station located in the Eastern Italian Alps. Its elevation and distance from major anthropogenic and natural sources make it ideal for monitoring baseline mercury levels and investigating its geochemical cycles. In this work, total gaseous mercury (TGM), ozone (O3) and meteorological variables were studied to investigate seasonal and diurnal variability of TGM measurements from March 2018 to May 2019. We found that the year-round mean TGM concentration was 1.8 times higher than the annual atmospheric mercury measurements previously reported during the GMOS project at the same measurement site. The seasonal variation of TGM was characterized by high values in spring and summer and lower values in winter. A systematic diel pattern of TGM was obtained, with low concentrations during the daytime and higher concentrations in the late evening. Spatial patterns and temporal changes in TGM, back-trajectories (BTs) and planetary boundary layer (PBL) analysis showed that total gaseous mercury levels were influenced by local meteorology, as well as regional and long-range transport of air masses. The lowest TGM concentrations in winter are associated with high wind speeds, low boundary layer height and cleaner air masses originating from the Western sector. Conversely, the highest TGM concentrations in spring and summer were attributed to polluted air masses passing over North-eastern and Continental Europe and were probably favoured by the higher PBL height. During the snow cover season, investigation of TGM peak events also demonstrated the potential influence of re-emission processes of previously reactive mercury deposition over snow surfaces.

Photon Recycling in CsPbBr3 All-Inorganic Perovskite Nanocrystals.

Photon recycling, the iterative process of re-absorption and re-emission of photons in an absorbing medium, can play an important role in the power-conversion efficiency of photovoltaic cells. To date, several studies have proposed that this process may occur in bulk or thin films of inorganic lead-halide perovskites, but conclusive proof of the occurrence and magnitude of this effect is missing. Here, we provide clear evidence and quantitative estimation of photon recycling in CsPbBr3 nanocrystal suspensions by combining measurements of steady-state and time-resolved photoluminescence (PL) and PL quantum yield with simulations of photon diffusion through the suspension. The steady-state PL shows clear spectral modifications including red shifts and quantum yield decrease, while the time-resolved measurements show prolonged PL decay and rise times. These effects grow as the nanocrystal concentration and distance traveled through the suspension increase. Monte Carlo simulations of photons diffusing through the medium and exhibiting absorption and re-emission account quantitatively for the observed trends and show that up to five re-emission cycles are involved. We thus identify 4 quantifiable measures, PL red shift, PL QY, PL decay time, and PL rise time that together all point toward repeated, energy-directed radiative transfer between nanocrystals. These results highlight the importance of photon recycling for both optical properties and photovoltaic applications of inorganic perovskite nanocrystals.

Fresnel Dragging Explained by a Classical Model of Light Transmission in Optical Media

The original mathematical treatment used in the analysis of the Fizeau experiment of 1851, which measured the relative speed of light in a moving medium, assumes that light travels through the water in a smooth continuous flow, at a speed less than the speed of light in a vacuum (relative to the water). Thus, it assumes that the water’s velocity vector can simply be added to that of the light. However, light is transmitted through optical media, such as water, by a continuous process of charge excitation (semi-absorption) and re-emission by the water molecules; but travels between them at the full speed of light (in a vacuum). Thus, the mathematics describing the process of Fresnel dragging must be formulated differently and can then be explained by classical physics, allowing the entire process to be fully visualized.

Spectrum of Single‐Photon Scattering in a Strong‐Coupling Hybrid Optomechanical System

AbstractThe single‐photon excitation and transmission spectra of strong‐coupling hybrid optomechanics are theoretically analyzed, where a two‐level system (TLS) is coupled to a mechanical resonator (MR), generating Jaynes–Cummings‐type polariton doublets. In this model, both the optomechanical coupling and the TLS‐MR coupling are strong. In this parameter region, polaron‐assisted excitation reemission processes can strongly affect the single‐photon excitation and output spectra of the cavity. It is found that the fine structure around each sideband can be used to characterize the TLS‐MR and the effective TLS‐photon couplings, even at the single‐quantum level. Thus, the spectrum structures may make it possible to sensitively probe the quantum nature of a macroscopic mechanical element. A possible approach for tomographic reconstruction of the state of a TLS, utilizing the single‐photon transmission spectra, is further provided.

A mechanism study on effects of bromide ion on mercury re-emission in WFGD slurry

The application of bromide-blended coal combustion technology can effectively improve the total mercury removal efficiency in coal-fired power plants. However, the effects of bromine introduced into WFGD slurry on the mercury re-emission process were still unclear. In this paper, the effects of Br- on mercury re-emission were studied in a bench-scale simulated WFGD system. The results indicated that Br- had an inhibitory effect on Hg0 re-emission. The mercury re-emission could be promoted with higher temperature, lower pH and moderate sulfite concentration in aqueous phase in the presence of Br-. The underlying mechanism of the inhibitory effect of Br- on Hg0 re-emission was proposed by combining experimental UV–visible spectra analyses with theoretical quantum chemistry calculations. It was found that the formation of BrnHgSO3n- (n = 1–3) complex and HgBr2 suppressed the reduction of Hg2+. The reason was that the BrnHgSO3n- complex and HgBr2 were more stable than HgSO3, whose decomposition is the main cause of mercury re-emission in WFGD in the solvent. Since the bromide-blended coal combustion technology can both oxidize elemental mercury and inhibit mercury re-emission, it has a good performance on mercury removal.

Can the ghost imaging increase the lateral resolution of surface plasmon resonance microscopy?

Surface plasmon resonance (SPR) microscopy is one of the most sensitive optical label-free methods of microscopy. Nevertheless, it does not have a sufficiently high lateral resolution in comparison with other methods of optical microscopy. By analogy with the scattering medium, surface plasmon polaritons (SPPs) blur the observed area. To eliminate this disadvantage, we propose to adapt the method known as ghost imaging (GI), which is notable for its tolerance to environmental aberrations between an object and a camera. In this article, we propose a ghost imaging scheme for a surface plasmon resonance microscope using a pseudo-thermal radiation source. We make a fundamental analysis of the factors affecting the resolution capability of the ghost SPR microscopy. We claim that applying the ghost imaging method to SPR microscopy can improve its lateral resolution by eliminating uncorrelated with modulated radiation phase noise generated by the process of random re-emission of surface electromagnetic wave (SEW) from the site of excitation. In combination of factors, the ghost imaging method of SPR microscopy is potentially capable of becoming outstanding among other methods of microscopy of thin films.

New insight into the photoinduced wavelength dependent decay mechanisms of the ferulic acid system on the excited states.

The ferulic acid (FA) is a kind of phenolic acid widely exists in nature plants. Apart from its medicinal values, the FA is also widely applied in cosmetic industry. Recently, it was found to have potential applications in commercial sunscreens for its strong photostability and photoprotection property from harmful UV rays. Such excellent property lies in the ultrafast decay process of the FA system when exposure to the UV light, but the underlying detailed relaxation pathway is still less clear-cut. In the current work, high-level ab initio electronic structure calculations and on-the-fly surface hopping dynamics simulations were employed to explore the photoinduced decay mechanism of the FA system both on the S1 and S3 states in the gas phase. The results provide a reasonable explanation for the wavelength dependent decay patterns of FA system. The S1 state decay pathway is driven by a re-emission process to dissipate excess energy. While for the S3 state deactivation process, the pathway is dominated by a non-adiabatic process driven by the internal conversion process through the conical intersection regions. A S3-S1-S0 two step decay pattern is proposed, and the pathways are mainly driven by a puckering distortion motion of the aromatic ring and a twisting motion around the bridging double bond. The calculation results contribute to a better understanding of detailed dynamics behavior of the FA deactivation process, and provide theoretical guidance for further design of efficient and environmentally friendly sunscreens.

A complete optical model for liquid-scintillator detectors

Liquid scintillator (LS) is widely used in various neutrino oscillation experiments, in particular, the reactor neutrino experiments. The complex absorption and re-emission processes of optical photons are known to be an important source of the non-linear and non-uniform response of LS detectors. Precise simulation of light propagation in LS is highly desirable to model the detector response and reduce the systematic errors. In this paper, we develop a novel optical model which can completely deal with the competitive photon absorption and subsequent re-emission processes of the LS components. It allows to directly plug in the laboratory measurements of the LS components to model any LS composition. Extensive measurements have been performed to obtain the essential optical parameters for this model. We validate the model with a bench-top experiment featuring a small LS volume. Furthermore, we demonstrate that for any given detector geometry, this model provides the capability of optimizing the LS recipe to maximize the light collection. It is valuable for designing future LS-based detectors and improving the agreement between Monte Carlo and data for current neutrino experiments.

Diurnal cycle of iodine, bromine, and mercury concentrations in Svalbard surface snow

Abstract. Sunlit snow is highly photochemically active and plays a key role in the exchange of gas phase species between the cryosphere and the atmosphere. Here, we investigate the behaviour of two selected species in surface snow: mercury (Hg) and iodine (I). Hg can deposit year-round and accumulate in the snowpack. However, photo-induced re-emission of gas phase Hg from the surface has been widely reported. Iodine is active in atmospheric new particle formation, especially in the marine boundary layer, and in the destruction of atmospheric ozone. It can also undergo photochemical re-emission. Although previous studies indicate possible post-depositional processes, little is known about the diurnal behaviour of these two species and their interaction in surface snow. The mechanisms are still poorly constrained, and no field experiments have been performed in different seasons to investigate the magnitude of re-emission processes Three sampling campaigns conducted at an hourly resolution for 3 d each were carried out near Ny-Ålesund (Svalbard) to study the behaviour of mercury and iodine in surface snow under different sunlight and environmental conditions (24 h darkness, 24 h sunlight and day–night cycles). Our results indicate a different behaviour of mercury and iodine in surface snow during the different campaigns. The day–night experiments demonstrate the existence of a diurnal cycle in surface snow for Hg and iodine, indicating that these species are indeed influenced by the daily solar radiation cycle. Differently, bromine did not show any diurnal cycle. The diurnal cycle also disappeared for Hg and iodine during the 24 h sunlight period and during 24 h darkness experiments supporting the idea of the occurrence (absence) of a continuous recycling or exchange at the snow–air interface. These results demonstrate that this surface snow recycling is seasonally dependent, through sunlight. They also highlight the non-negligible role that snowpack emissions have on ambient air concentrations and potentially on iodine-induced atmospheric nucleation processes.

A multigroup moment-accelerated deterministic particle solver for 1-D time-dependent thermal radiative transfer problems

We propose an efficient, robust, Lagrangian (characteristic-based) transport solver for 1-D time-dependent thermal radiative transfer (TRT) applications within the context of a moment-accelerated (High-Order/Low-Order, HOLO) algorithm. This novel transport algorithm inherits the best features of both particle methods (e.g., time accuracy, phase-space adaptivity, positivity) and deterministic, grid-based methods (e.g., no stochastic noise). Particles are evolved by the method of characteristics, with a time-dependent weight that accounts for stiff absorption and reemission process self-consistently. As a result, this approach is able to obtain accurate results while employing large time steps and a moderate number of particles (compared to Implicit Monte Carlo).

Mercury Isotopic Fractionation during Pedogenesis in a Tropical Forest Soil Catena (French Guiana): Deciphering the Impact of Historical Gold Mining.

We used natural mercury (Hg) stable isotopes to investigate the Hg cycle in a rainforest soil catena (French Guiana) partially gold-mined during the early 1950s. Litterfall showed homogeneous Δ199Hg values [-0.18 ± 0.05‰, i.e., a modern gaseous elemental Hg (GEM) isotopic signature]. After litter decomposition, Hg bound to organic matter (OM) is mixed with Hg from pristine (-0.55 ± 0.22‰) or gold-mined (-0.09 ± 0.16‰) mineral materials. Negative Δ199Hg values in deep pristine mineral horizons (-0.60 ± 0.16‰) suggest the transfer of Hg bound to dissolved OM depleted in odd isotopes due to mass-independent fractionation during Hg abiotic reduction. Perennial palm tree leaves collected above gold-mined and pristine soil recorded contrasting Δ199Hg signatures likely resulting from GEM re-emission processes from soils and leaf surfaces. Upslope, soil δ202Hg signatures showed a negative shift (ε ∼ -1‰) with depth attributed to mass-dependent fractionation during Hg sorption and complexation onto iron oxides and dissolved OM. Downslope, higher δ202Hg values in soils resulted from hydromorphy [lower humification, greater Hg(II) reduction, etc.]. The unique Hg isotopic signatures of Amazonian soils probably result in multistep fractionation processes during pedogenesis (millions of years) and in a potentially different Hg isotopic signature of preanthropogenic background GEM.

Work on a quantum dipole by a single-photon pulse.

Energy transfer from a quantized field to a quantized dipole is investigated. We find that a single photon can transfer energy to a two-level dipole by inducing a dynamic Stark shift, going beyond the well-known absorption and emission processes. A quantum thermodynamical perspective allows us to unravel these two energy transfer mechanisms and to identify the former as a generalized work and the latter as a generalized heat. We show two necessary conditions for the generalized work transfer by a single photon to occur, namely, off-resonance and finite linewidth of the pulse. We also show that the generalized work performed by a single-photon pulse equals the reactive (dispersive) contribution of the work performed by a semiclassical pulse in the low-excitation regime.

Impacts of anthropogenic source from the nuclear fuel reprocessing plants on global atmospheric iodine-129 cycle: A model analysis

Abstact The long-lived radioactive iodine (129I) is a useful geochemical tracer of radioactivity in the atmospheric environment. Although the behavior of 129I in the atmosphere is still not fully known because of lack of continuous monitoring, we recently observed clear seasonal trends in air concentration and deposition of 129I in Japan. Using these data, we developed a global atmospheric 129I transport model to reveal key processes for the global atmospheric 129I cycle. The physical and chemical processes of advection, turbulent diffusion, dry and wet deposition, atmospheric photolysis, gas–particle conversion in the atmosphere, anthropogenic sources of 129I discharged from operating nuclear fuel reprocessing plants, and natural sources of 129I volatilized from ocean and land were included into the model. The model generally reproduced the observed seasonal change in monthly air concentration and deposition of 129I in Japan, and the global distribution of 129I concentration in rain as presented in past literature. Numerical experiments changing the intensity of anthropogenic and natural sources were conducted to quantify the impact of anthropogenic sources on the global 129I cycle. The results indicated that the atmospheric 129I from the anthropogenic sources was readily deposited in winter and can be accumulated mainly in the northern part of Eurasia. In contrast, the atmospheric 129I from the natural sources dominated the deposition in summer. These results suggested that the re-emission process of 129I from the Earth's surface may be important as a secondary impact of 129I in the global-scaled environment. Furthermore, although wet deposition dominated the total deposition in the Northern hemisphere, dry deposition regionally and seasonally contributed to the total deposition over arctic and northern part of Eurasia in winter, suggesting that the dry deposition may play a key role in the seasonal change of 129I deposition in the high latitudes of the Northern hemisphere.