Attenuation Length Research Articles

Study on the Aging of the BGO Calorimeter of the DAMPE Experiment in Space

The DArk Matter Particle Explorer (DAMPE) has been in operation stably for nearly seven years. The key sub-detector of DAMPE is the BGO electromagnetic calorimeter, which consists of 308 BGO crystal bars. As a long-term apparatus in space, the BGO calorimeter faces continuous radiation bombardment, and therefore the radiation resistance of the BGO is crucial for the performance of energy measurement. In order to understand the aging of BGO crystals caused by radiation in space, the stability including attenuation length and the absolute energy scale has been examined with on-orbit data over 6.5 years. The aging effects are found in the BGO crystals of the inner and outer parts of the BGO calorimeter. Due to real-time calibration, the BGO calorimeter is still in a stable operation status.

Quantitative alignment parameter estimation for analyzing X-ray photoelectron spectra.

The interpretation of X-ray photoelectron spectroscopy (XPS) data relies on measurement models that depend on several parameters, including the photoelectron attenuation length and X-ray photon flux. However, some of these parameters are not known, because they are not or cannot be measured. The unknown geometrical parameters can be lumped together in a multiplicative factor, the alignment parameter. This parameter characterizes the ability of the exciting light to interact with the sample. Unfortunately, the absolute value of the alignment parameter cannot be measured directly, in part because it depends on the measurement model. Instead, a proxy for the experimental alignment is often estimated, which is closely related to the alignment parameter. Here, a method for estimating the absolute value of the alignment parameter based on the raw XPS spectra (i.e. non-processed photoelectron counts), the geometry of the sample and the photoelectron attenuation length is presented. The proposed parameter estimation method enables the quantitative analysis of XPS spectra using a simplified measurement model. All computations can be executed within the open and free Julia language framework PROPHESY. To demonstrate feasibility, the alignment parameter estimation method is first tested on simulated data with known acquisition parameters. The method is then applied to experimental XPS data and a strong correlation between the estimated alignment parameter and the typically used alignment proxy is shown.

6Li-loaded liquid scintillators produced by direct dissolution of compounds in diisopropylnaphthalene (DIPN)

The paper describes preparation of 6Li-loaded liquid scintillators by methods involving direct dissolution of 6Li salts in the commercial diisopropylnaphthalene (DIPN) solvent, without the formation of water-in-oil emulsions. Methods include incorporation of 6Li that, unlike previously reported formulations, does not require additions of water or a strong acid such as hydrochloric acid (HCl). Results of the conducted experiments show that dissolution of aromatic and aliphatic 6Li salts in DIPN can be easily achieved at 0.1%–0.3% by weight of atomic 6Li, using small additions of waterless surfactants, or mild carboxylic acids. An alternative way suggests incorporation of 6Li as a part of a surfactant molecule that can be dissolved in DIPN without any solubilizing additions. Proposed methods enable preparation of efficient 6Li-loaded liquid scintillators that, at a large scale of 50 cm, exhibit good pulse shape discrimination (PSD) properties combined with up to 107% of light output and up to 115% of the attenuation length measured relative to standard undoped EJ-309 liquid scintillator.

Piezo‐Phototronic Effect‐Induced Self‐Powered Broadband Photodetectors using Environmentally Stable α‐CsPbI3 Perovskite Nanocrystals

AbstractUtilizing the remarkably high light absorption and long carrier diffusion length of inorganic perovskites, superior performance self‐powered broadband photodetectors using the vertical heterojunction of cesium lead iodide (CsPbI3) nanocrystals (NCs) and zinc oxide (ZnO) films on a flexible platform are reported. Here, the pure cubic or α‐phase of as‐synthesized CsPbI3 NCs facilitate the novelty of the present work in terms of their enhanced structural stability suitable for optical applications. The α‐CsPbI3/ZnO device exhibits superior performance with photoresponsivity of ≈8.2 AW−1, ON/OFF ratio of ≈2.4 × 104, and specific detectivity up to ≈1.4 × 1012 Jones. Furthermore, the piezo‐phototronic effect of ZnO has been exploited to enhance the device performance by utilizing the compressive strain‐induced piezoelectric charges for modulating the generation, separation, and transportation of charge carriers. By introducing an approximate −0.042% compressive strain in the hybrid heterostructure, the enhancement of photocurrent, spectral responsivity, and specific detectivity of the detector by ≈619%, ≈536%, and ≈506%, respectively, under visible light illumination has been successfully achieved. This work not only presents an inventive method for improving the performance of perovskite photodetectors through interface engineering, but it also provides a thorough understanding of the piezo‐phototronic effect on optoelectronic devices.

A new neutron-gamma porosity measurement method for pulsed neutron logging tools

As an alternative method for the compensated neutron porosity measurement method, the neutron-gamma porosity measurement method is widely used in cased holes. However, the neutron-gamma porosity measurement method has some problems, such as the lack of detailed theoretical analysis and low sensitivity in high-porosity formations. The purpose of this paper is to clarify the theory of neutron-gamma porosity measurement, improve the measurement sensitivity, and eliminate the effects of environmental factors. Based on the neutron diffusion theory and the gamma transport theory, the distribution of capture gamma rays is described. A new neutron-gamma porosity measurement method is developed based on inelastic and capture gamma-ray distribution. The applicability of the new method in different environments is analyzed using the Monte Carlo method, and the effectiveness of this method is verified using the synthetic model. The results indicate that the capture gamma-ray ratio is only related to the source-detector distance, gamma-ray attenuation length, and neutron migration length. By combining density, different neutron cross sections, inelastic gamma-ray count ratio, and capture gamma-ray count ratio, the parameter secondary gamma-ray hydrogen index (SGH) related to hydrogen index can be extracted. The dynamic range of SGH is much higher than thermal neutron count ratio and the capture gamma-ray count ratio. The errors in porosity calculation by this method under different borehole and lithologic conditions are generally less than 2 pu. The calculation error of this method is close to that of the compensated neutron porosity measurement method. In addition, the applicability of the new method is analyzed without density data, and the results indicate that the calculation results are basically consistent with the results of calculation with density data. The new method has great potential for extensive applications in cased holes or open holes as an alternative for the compensated neutron porosity logging measurement method.

Submerged single-photon LiDAR imaging sensor used for real-time 3D scene reconstruction in scattering underwater environments.

We demonstrate a fully submerged underwater LiDAR transceiver system based on single-photon detection technologies. The LiDAR imaging system used a silicon single-photon avalanche diode (SPAD) detector array fabricated in complementary metal-oxide semiconductor (CMOS) technology to measure photon time-of-flight using picosecond resolution time-correlated single-photon counting. The SPAD detector array was directly interfaced to a Graphics Processing Unit (GPU) for real-time image reconstruction capability. Experiments were performed with the transceiver system and target objects immersed in a water tank at a depth of 1.8 meters, with the targets placed at a stand-off distance of approximately 3 meters. The transceiver used a picosecond pulsed laser source with a central wavelength of 532 nm, operating at a repetition rate of 20 MHz and average optical power of up to 52 mW, dependent on scattering conditions. Three-dimensional imaging was demonstrated by implementing a joint surface detection and distance estimation algorithm for real-time processing and visualization, which achieved images of stationary targets with up to 7.5 attenuation lengths between the transceiver and the target. The average processing time per frame was approximately 33 ms, allowing real-time three-dimensional video demonstrations of moving targets at ten frames per second at up to 5.5 attenuation lengths between transceiver and target.

Long range 3D imaging through atmospheric obscurants using array-based single-photon LiDAR.

Single-photon light detection and ranging (LiDAR) has emerged as a strong candidate technology for active imaging applications. In particular, the single-photon sensitivity and picosecond timing resolution permits high-precision three-dimensional (3D) imaging capability through atmospheric obscurants including fog, haze and smoke. Here we demonstrate an array-based single-photon LiDAR system, which is capable of performing 3D imaging in atmospheric obscurant over long ranges. By adopting the optical optimization of system and the photon-efficient imaging algorithm, we acquire depth and intensity images through dense fog equivalent to 2.74 attenuation lengths at distances of 13.4 km and 20.0 km. Furthermore, we demonstrate real-time 3D imaging for moving targets at 20 frames per second in mist weather conditions over 10.5 km. The results indicate great potential for practical applications of vehicle navigation and target recognition in challenging weather.

A2Bn-1PbnI3n+1 (A = BA, PEA; B = MA; n = 1, 2): Engineering Quantum-Well Crystals for High Mass Density and Fast Scintillators.

Quantum-well (QW) hybrid organic-inorganic perovskite (HOIP) crystals, e.g., A2PbX4 (A = BA, PEA; X = Br, I), demonstrated significant potentials as scintillating materials for wide energy radiation detection compared to their individual three-dimensional (3D) counterparts, e.g., BPbX3 (B = MA). Inserting 3D into QW structures resulted in new structures, namely A2BPb2X7 perovskite crystals, and they may have promising optical and scintillation properties toward higher mass density and fast timing scintillators. In this article, we investigate the crystal structure as well as optical and scintillation properties of iodide-based QW HOIP crystals, A2PbI4 and A2MAPb2I7. A2PbI4 crystals exhibit green and red emission with the fastest PL decay time <1 ns, while A2MAPb2I7 crystals exhibit a high mass density of >3.0 g/cm3 and tunable smaller bandgaps <2.1 eV resulting from quantum and dielectric confinement. We observe that A2PbI4 and PEA2MAPb2I7 show emission under X- and γ-ray excitations. We further observe that some QW HOIP iodide scintillators exhibit shorter radiation absorption lengths (∼3 cm at 511 keV) and faster scintillation decay time components (∼0.5 ns) compared to those of QW HOIP bromide scintillators. Finally, we investigate the light yields of iodide-based QW HOIP crystals at 10 K (∼10 photons/keV), while at room temperature they still show pulse height spectra with light yields between 1 and 2 photons/keV, which is still >5 times lower than those for bromides. The lower light yields can be the drawbacks of iodide-based QW HOIP scintillators, but the promising high mass density and decay time results of our study can provide the right pathway for further improvements toward fast-timing applications.

Development of a Stable Oxygen Sensor Using a 761 nm DFB Laser and Multi-Pass Absorption Spectroscopy for Field Measurements.

An optical sensor system based on wavelength modulation spectroscopy (WMS) was developed for atmospheric oxygen (O2) detection. A distributed feedback (DFB) laser with butterfly packaging was used to target the O2 absorption line at 760.89 nm. A compact multi-pass gas cell was employed to increase the effective absorption length to 3.3 m. To ensure the stability and anti-interference capability of the sensor in field measurements, the optical module was fabricated with isolation of ambient light and vibration design. A 1f normalized 2f WMS (WMS-2f/1f) technique was adopted to reduce the effect of laser power drift. In addition, a LabVIEW-based dual-channel lock-in amplifier was developed for harmonic detection, which significantly reduced the sensor volume and cost. The detailed detection principle was described, and a theoretical model was established to verify the effectiveness of the technique. Experiments were carried out to obtain the device's sensing performances. An Allan deviation analysis yielded a minimum detection limit of 0.054% for 1 s integration time that can be further improved to 0.009% at ~60 s. Finally, the reliability and anti-interference capability of the sensor system were verified by the atmospheric O2 monitoring.

Demonstration of 12.5 Mslot/s 32-PPM Underwater Wireless Optical Communication System with 0.34 Photons/Bit Receiver Sensitivity

High-capacity, long-distance underwater wireless optical communication (UWOC) technology is an important component in building fast, flexible underwater sensing networks. Underwater communication with light as a carrier has a large communication capacity, but channel loss induced by light attenuation and scattering largely limits the underwater wireless optical communication distance. To improve the communication distance, a low-power 450 nm blue continuous wave (CW) laser diode (LD)-based UWOC system was proposed and experimentally demonstrated. A communication link was designed and constructed with a BER of 3.6 × 10−3 in a total link loss of 80.72 dB in c = 0.51 m−1 water with a scintillation index (S.I.) equal to 0.02 by combining with 32-pulse-position modulation (32-PPM) at a bandwidth of 12.5 MHz and single photon counting reception techniques. The allowable underwater communication distance in Jerlov II (c = 0.528 m−1) water was estimated to be 35.64 m. The attenuation lengths were 18.82, which were equal at link distances of 855.36 m in Jerlov I (c = 0.022 m−1) water. A receiving sensitivity of 0.34 photons/bit was achieved. To our knowledge, this is the lowest receiving sensitivity ever reported under 0.1 dB of signal-to-noise ratio (SNR) in the field of UWOC.

Theoretical investigation of silicon thin film solar cell for improving short and long wavelength response

Theoretical investigation or numerical simulation of performance of a solar cell can provide useful information to maximize power conversion efficiency. In that respect we carried out a set of numerical simulation using AFORS-HET simulation program. Separately the optical absorption of the individual layers of thin film solar cell was analyzed. Current-voltage characteristic curve of a reference cell (Cell-A) was used as the starting device. The power conversion efficiency (PCE) of the reference device was 8.85% with short circuit current density (Jsc) of 15.43 mA/cm2 and fill factor (FF) of 68.3%. After suitable optimization the PCE of this device (Cell-B2) improves to 11.59% (Jsc and FF became 13.0 mA/cm2 and 87% respectively). The results show that the effective optical absorption in the active layer can be improved significantly by optimizing the device structure. The short wavelength response can be improved by reducing the parasitic optical absorption of the doped window layer, while the long wavelength response improves by raising effective absorption length of the active layer. Furthermore, optimum thickness of the active layer, for the highest possible PCE, is found to be dependent upon its defect density.

Determining the volume fraction in 2-phase composites and bodies using time varying applied fields

A body Θ containing two phases, which may form a periodic composite with microstructure much smaller that the body, or which may have structure on a length scale comparable to the body, is subjected to slowly time varying boundary conditions that would produce an approximate uniform field in Θ were it filled with homogeneous material. Here slowly time varying means that the wavelengths and attenuation lengths of waves at the frequencies associated with the time variation are much larger than the size of Θ, so that we can make a quasistatic approximation. At least one of the two phase does not have an instantaneous response but rather depends on fields at prior times. The fields may be those associated with electricity, magnetism, fluid flow in porous media, or antiplane elasticity. We find, subject to these approximations, that the time variation of the boundary conditions can be designed so boundary measurements at a specific time t=t0 exactly yield the volume fractions of the phases, independent of the detailed geometric configuration of the phases. Moreover, for specially tailored time variations, the volume fraction can be exactly determined from measurements at any time t, not just at the specific time t=t0. We also show how time varying boundary conditions, not oscillating at the single frequency ω0, can be designed to exactly retrieve the response at ω0.

PEA2PbI4: fast two-dimensional lead iodide perovskite scintillator with green and red emission

Among the two-dimensional hybrid organic-inorganic perovskites, PEA2PbBr4 is one of the best scintillators combining high light yield and fast nanosecond decay time. However, it has limited sensitivity to X-ray and positron emission tomography because of insufficient mass density and effective atomic number. In this article, we show that exchanging the halide from bromide to iodide allows to shorten the absorption length as much as two times for X-ray energies. We present a detailed study on scintillation properties of self-grown samples of PEA2PbI4 crystal, which we compare with the previously reported results for PEA2PbBr4 crystal. The synthesis method of PEA2PbI4 crystal is based on dissolving the perovskite precursors in hydroiodic acid, which is then stirred and left for evaporation. Our measurements include the characterizations with optical, X-ray, and γ-ray sources. We observe two emission bands of PEA2PbI4 crystal centered at 532 (green) and 660 (red) nm, and we link them to the scintillation mechanisms involving exciton and surface defect states. We also report the scintillation light yields of 1,000 and 10,000 photons/MeV at room temperature and 10 K, respectively, and the coincidence timing resolution full width at half maximum of 138 ps, and the fast component in scintillation decay curve of 0.5 ns. This fast component is much faster than that of 13.4 ns of PEA2PbBr4 crystal, and with two times shorter absorption length, it secures better opportunities in timing applications in particular time-of-flight positron emission tomography and high energy physics.

Comparative studies of plastic scintillator strips with high technical attenuation length for the total-body J-PET scanner

Plastic scintillator strips are considered as one of the promising solutions for the cost-effective construction of total-body positron emission tomography, (PET) system. The purpose of the performed measurements is to compare the transparency of long plastic scintillators with dimensions 6 mm × 24 mm × 1000 mm and with all surfaces polished. Six different types of commercial, general purpose, blue-emitting plastic scintillators with low attenuation of visible light were tested, namely: polyvinyl toluene-based BC-408, EJ-200, RP-408, and polystyrene-based Epic, SP32 and UPS-923A. For determination of the best type of plastic scintillator for total-body Jagiellonian positron emission tomograph (TB-J-PET) construction, emission and transmission spectra, and technical attenuation length (TAL) of blue light-emitting by the scintillators were measured and compared. The TAL values were determined with the use of UV lamp as excitation source, and photodiode as light detector. Emission spectra of investigated scintillators have maxima in the range from 420 nm to 429 nm. The BC-408 and EJ-200 have the highest transmittance values of about 90% at the maximum emission wavelength measured through a 6 mm thick scintillator strip and the highest technical attenuation length reaching about 2000 mm, allowing assembly of long detection modules for time-of-flight (TOF) J-PET scanners. Influence of the 6 mm × 6 mm, 12 mm × 6 mm, 24 mm × 6 mm cross-sections of the 1000 mm long EJ-200 plastic scintillator on the TAL and signal intensity was measured. The highest TAL value was determined for samples with 24 mm × 6 mm cross-section.

Quantification of the Shell Thickness of Tin Oxide/Gold Core–Shell Nanoparticles by X-ray Photoelectron Spectroscopy

Encapsulation of nanoparticles (NP) by a shell material provides characteristics and properties not achievable by the individual materials of the core and the shell. Therefore, the characterization of morphology parameters of core–shell nanoparticles (CSNP) is critical to determine their performance. In this work, an analysis to determine the shell thickness of CSNP has been conducted using a simple and noniterative procedure known as Shard’s methodology, where the conversion of XPS peak intensities into shell thickness can be performed. Implementing the Simulation of Electron Spectra for Surface Analysis (SESSA), we acquired an insight into the morphology and composition of the CSNP by simulating the spectra from XPS to extract the parameters (Shard’s methodology) and confirm the core–shell ratio with experimental spectra to quantify the shell thickness. The CSNPs were synthesized with reverse micelle templating using diblock copolymer micellar templates, using various ratios of tin and gold precursors to form SnO2@Au core–shell nanoparticles. Considering elastic-scattering effects, a good agreement was found in the quantification of the shell thicknesses with a variation inside the ±10% regime of the effective attenuation length (EAL). This work demonstrates the use of simulation software as a complementary tool to a multitechnique analysis for a detailed understanding of CSNP.

Pt-single atom decorated TiO2: Tuning anodic TiO2 nanotube structure and geometry toward a high-performance photocatalytic H2 production

Atomically dispersed Pt single atoms (SAs) on titania have been reported to be a highly effective co-catalyst in photocatalytic H2 generation. In this report, we grew layers of anodic TiO2 nanotubes (NTs) varying the lengths of the NTs from 1 to 18 μm as well as their crystalline state by thermal annealing over a wide range of temperatures (350 °C – 800 °C). We then decorated the nanotubes with single atom (SA) Pt co-catalysts deposited from H2PtCl6 solutions with various concentrations of 0.001–2 mM Pt and evaluate the photocatalytic H2 generation performance for the different NT layers under UV and solar illumination. The highest photocatalytic performance is achieved for 15–18 μm long anatase NTs decorated with Pt SAs from a 0.01 mM H2PtCl6 solution (leading to a Pt SA surface concentration of 5.6 × 105 /µm2). Except for a sufficient SA Pt loading and an anatase structure, the key parameter is the photon absorption length for near-band-gap UV and AM 1.5 light. Such optimized Pt SA@TiO2 NTs show a most efficient H2, outperforming many other photocatalytic 3D titania structures, such as titania-based powders, flakes, and Metal–Organic Frameworks (MOFs) tested under the same illumination conditions.

Simple model of morphometric constraint on carbon burial in boreal lakes

A geometric theory was developed to explain the empirical relationship between carbon burial and lake shape in boreal lakes. The key feature of this model is an attenuation length scale, analogous to models of marine organic carbon fluxes. This length scale is the ratio of how fast carbon is displaced vertically versus how fast it is respired and engenders a simple model with a single easily constrained free parameter. Lake depths are modeled based on fractal area–volume relationships that reflect the approximate scale invariance of Earth’s topography on idealized lake geometries. Carbon burial is estimated by applying the attenuation length scale to these depths. Using this model, we demonstrate the relationship between the dynamic ratio—a metric of lake morphometry calculated by dividing the square root of surface area by the mean depth—and carbon burial. We use scaling relationships to predict how dynamic ratio, and by extension carbon burial, varies across the lake size spectrum. Our model also provides a basis for generalizing empirical studies to the biome scale. By applying our model to a boreal lake census, we estimate boreal lake carbon burial to be 1.8 ± 0.5 g C/m2/yr or 1.1 ± 0.3 Tg C/yr among all boreal lakes.

Hybridization‐Induced Spin‐Wave Transmission Stop Band within a 1D Diffraction Grating

AbstractSpin wave propagation is studied through a diffraction grating in a 200 nm thick YIG film by using scanning time resolved magneto‐optic Kerr microscopy (TR‐MOKE) and supported by micromagnetic simulations. Caustic‐like spin wave emission and the hybridization of Damon Eshbach (DE) type spin wave modes within the grating region, depending on the magnetic field and the dimensions of the grating, are observed. Hybridization leads to an increased attenuation length for propagating spin waves and consequently to a transmission stop‐band for spin waves at the grating for a certain magnetic field range.

Material removal on silicon towards atomic and close-to-atomic scale by infrared femtosecond laser

Ultrashort laser pulse is a widely used tool for high precision machining. However, the understanding on its minimum removal is still unclear. In this paper, single laser pulse (232 fs at 1030 nm) is used to study material removal of silicon from its (001) surface at near threshold fluence. The damage threshold, effective attenuation length, removal depth and ablation morphology are investigated systematically using atomic force microscopy. The minimum material removal of down to 1 nm is observed experimentally. A novel molecular dynamics method coupled with two temperature model is developed to reveal multiphoton ionization and explore the dynamic process. Results show that laser-induced plasma plays important role in the interaction process. The ablation crater is generated by plasma ejection and the outer rim around the crater is formed by the recoil pressure due to high pressure plasma expanding.

Silicon Waveguide Sensors for Carbon Dioxide Gas Sensing in the Mid-Infrared Region

Two optical waveguide sensors based on SOS (silicon-on-sapphire) for detecting CO2 are theoretically proposed. The operational wavelength is 4.23 μm, which is the maximum absorption line of CO2. The power confinement factor (η) value is over 40% and 50%, the propagation loss is 0.98 dB/cm and 2.99 dB/cm, respectively, in the slot waveguide and SWGS (subwavelength grating slot) waveguide. An inverted tapered structure is used for the transition from strip waveguide to slot waveguide and constitutes the sensing absorption region, with the coupling efficiency that can reach more than 90%. When the optimal absorption length of the slot waveguide and SWGS waveguide is 1.02 cm and 0.33 cm, respectively, the maximum sensitivity can reach 6.66 × 10−5 (ppm−1) and 2.60 × 10−5 (ppm−1). Furthermore, taking the slot waveguide as an example, spiral and meander structures enable the long-distance sensing path to integrate into a small area.