Angular Scatter Research Articles

Diamond-like carbon conversion surfaces for space applications

We present diamond-like carbon (DLC) conversion surfaces to detect particles with energy below 2 keV. Conversion surfaces have been widely applied in measurements of low-energy particles by instruments onboard planetary and heliophysics missions. Their effectiveness is characterized by the efficiency in changing the charge state of the incident particles while maintaining a narrow angular distribution for the reflected particles. DLC as a conversion surface coating material has high conversion efficiency. We developed a conversion surface production process that provides ultra-smooth and ultra-thin DLC conversion surfaces. The process includes substrate preparation through precision cleaning, plasma immersion ion deposition of the DLC film, and diagnostics of the film parameters. The latter includes the measurement of the coating thickness, surface roughness, and the conversion efficiency for ion beams with energy below 2 keV. The process we developed provides the DLC conversion surface coating of repeatable parameters with a mean surface roughness of 3.4 ± 0.2 Å and a mean film thickness of 46.7 ± 0.8 nm uniform across the sample area. Ion beam measurements showed a negative ion yield of 1%–2% for hydrogen atoms and 8%–15% for oxygen atoms with an angular scatter distribution of 10°–20° at full width of half maximum. These results agree with those of other conversion surface coatings in the literature. The DLC conversion surfaces presented here are implemented in the conversion surface subsystem of the Interstellar Mapping and Acceleration Probe (IMAP)-Lo instrument of the IMAP mission scheduled for launch in 2025.

Evaluating the capability of detecting recoil-electron tracks using an electron-tracking Compton camera with a silicon-on-insulator pixel sensor

Sub-MeV gamma-ray line observations are crucial for the understanding of high-energy astrophysical processes. In this energy range, the presence of a significant amount of background poses a serious problem. Therefore, it is essential to reduce this background to achieve high-sensitivity observations. An electron-tracking Compton camera can efficiently mitigate the impact of background on scientific results thanks to its ability to fully resolve the Compton process. In addition if we utilize a semiconductor detector as the sensor, the electron-tracking Compton camera can achieve high-energy resolution for the detection of gamma-ray lines. To operate the electron-tracking Compton camera effectively, the sensor needs to coincidence events for each detection signal and resolve the complex structure of recoiled-electron tracks of a few hundred μm. We focused on the silicon-on-insulator pixel sensor XRPIX2b developed for X-ray observations, which satisfies requirements. We developed a prototype electron-tracking Compton camera using XRPIX2b and carried out a quantitative evaluation of its detection capability for estimating the recoil directions of electrons at various angles. As a result, we successfully detected short recoil-electron tracks with a length of 100μm corresponded to scattering angles of 30°-40° for 511 keV gamma rays entering the sensor. In term of angular resolution measure and scatter plane deviation of a reconstructed image, the evaluations showed results of 15° and 40° (full width at half maximum), respectively, in cases where 511 keV gamma rays were scattered at 90° and recoil electrons tracked the surface of the sensor detection plane. We confirmed that these results were consistent with simulation results, within approximately a 15% margin.

On the missing single collision peak in low energy heavy ion scattering

We present experimental and simulation data on the oblique angle scattering of heavy Sn ions at 14keV energy from a Mo surface. The simulations are performed with the binary collision approximation codes TRIM, TRIDYN, TRI3DYN, SDTrimSP, and IMSIL. Additional simulations were performed in the molecular dynamics framework with LAMMPS. Our key finding is the absence of an expected peak in the experimental energy spectrum of backscattered Sn ions associated with the pure single collision regime. In sharp contrast to this, however, all simulation codes we applied do show a prominent single collision signature both in the energy spectrum and in the angular scatter pattern. We discuss the possible origin of this important discrepancy and show in the process, that widely used binary collision approximation codes may contain hidden parameters important to know and to understand.

Dirac cones in graphene grown on a half-filled 4d-band transition metal

New opportunities for structural and electronic properties engineering of graphene can be achieved by tuning the interfacial interaction, which is ruled by the interplay between d-band filling and geometry of the support. Here, is demonstrated the growth of graphene, featuring Dirac cones around the Fermi level, on the rectangular (110) surfaces of Rh, a half-filled 4d-band transition metal element. The analysis of the structural properties by low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) shows that domains with a continuum of possible graphene-substrate orientations with angular scatter of around 10° coexist in graphene/Rh(110) surfaces. Within each domain, surface structure is characterized by a distinct stripe-like moiré pattern. The interfacial chemistry analysis, by microprobeX-ray photoelectron spectroscopy (μ-XPS), of all the rotational domains studied, demonstrates the existence of two main levels of interfacial interaction strength, similar to previously reported graphene-metal systems characterized by the absence of Dirac cones around the Fermi level. However, the band structures of these domains probed by micro angle resolved photoelectron spectroscopy (μ-ARPES) present Dirac cones, with Fermi velocities comparable with those previously reported on weakly coupled graphene layers. Both the unique properties of graphene/Rh(110) surfaces and the prospect to obtain novel graphene-metal interfaces through the interplay between d-band filling and geometry, are expected to open new opportunities to study phenomena up to now masked behind the interaction with the substrate.

A Simple Analytical Model for Oil Production from Partially Fractured Reservoirs to Estimate Size of Finite Fracture Networks

Summary Most oil reservoirs are partially fractured, characterized by finite fracture networks (FFNs) in a sea of isolated fractures. It is necessary to determine size and shape of each FFN explicitly for reservoir simulation. FFN size is correlated with fracture connectivity, which is a function of fracture density, length, and angular scatter. Oil production from FFNs exhibits a long-term dual-porosity behavior. The initial fast rate (Phase I) represents depletion of matrix within FFN, and the subsequent gradual decline phase represents radial flow from the matrix outside the FFN perimeter. Thus, FFN size can be calculated from the cumulative oil production from Phase I, taking into account the pore volume, oil compressibility, and pressure decline. It is not always possible to identify the dual-porosity behavior by visual inspection. A mathematical model is needed to estimate FFN size. For this purpose, a set of three fundamental equations are derived for production rate, cumulative production, and pressure as a function of time. The model is a modified and simplified version of material balance equations with easy analytical solution. It is designed for fractured reservoirs with layer-bound fractures. Production is single-phase black oil under depletion drive. The analytical model was tested on four vertical wells. The unknown parameters such as FFN size, size of well drainage area, and fracture aperture are adjusted until an optimum fit to actual production data is obtained. FFN elliptical shape is estimated from average fracture strike and strike standard deviation. The results are validated by FFN size, fracture length, and aperture measurements from borehole images. The results are approximate but sufficient for preliminary mapping of FFNs with location and size and other critical attributes including fracture drainage area, matrix block size, fracture aperture, and permeability in partially fractured reservoirs.

Development of local plasticity around voids during tensile deformation

Voids can limit the life of engineering components. This motivates us to understand local plasticity around voids in a nickel base superalloy combining experiments and simulations. Single crystal samples were deformed in tension with in-situ high angular resolution electron back scatter diffraction to probe the heterogeneous local stress field under load; the reference stress is informed by crystal plasticity finite element simulations. This information is used to understand the activation of plastic deformation around the void. Our investigation indicates that while the resolved shear stress would indicate slip activity on multiple slip systems, slip is reduced to specific systems due to image forces and forest hardening. This study rationalizes the observed development of plastic deformation around the void, aiding in our understanding of component failure and engineering design.

Narrow-angle scatter of reflectivity-suppressing nanostructured surfaces

Antireflective nanostructured surfaces (ARSS) enhance optical transmission through suppression of Fresnel reflection at boundaries between layered media. Previous studies show that random ARSS (rARSS) exhibit broadband enhancement and polarization insensitivity in transmission when applied to flat optical windows. Zinc selenide windows with rARSS treatment were fully characterized (transmittance, reflectance, and angular scatter) in the midwave and long-wave infrared range (2 to 12 μm). Four morphologically different, random nanoroughness, antireflective surfaces were tested at: normal incidence transmission, at 15 deg angle of incidence, and 15 deg to 45 deg angle of reflection. The angular reflectance distribution resembles a diffuse dipole radiator due to the finite elongated beam cross section at the incidence surface. Scattering diagrams with main and side lobes are presented. Partially integrated scatter values were obtained, allowing the comparison of random antireflective boundary performance to optically flat surfaces. Comparing axial transmission and specular reflection with the scattered performance, an accurate determination of the redistribution of the incident energy is obtained. Measurements of the rARSS feature topology were determined from autocorrelation of the scanning electron microscope images of the nanoroughened substrates, to assess the structured surfaces’ feature scales. The results show differences in scattered intensity over the wavelength bands of interest, correlating with surface random feature populations.

A non-local crystal plasticity constitutive model for hexagonal close-packed polycrystals

A strain gradient crystal plasticity finite element model is developed to study the evolution of internal and localized elastic strains in hexagonal close-packed polycrystals. The results of the model are firstly compared to the previously published data for a series of in-situ neutron diffraction experiments conducted on α-zirconium specimens. The development of internal lattice strains is studied first without considering the possible effects of grain morphologies and locations. This is followed by importing the “as-measured” grain maps into the model, and investigating the development of localized lattice rotation fields, geometrically necessary dislocation densities, and statistically stored dislocation densities in the vicinity of twins. The numerical results are compared to those measured for a deformed α-zirconium specimen using high angular resolution electron back scatter diffraction technique. To understand the benefits of using non-local formulation, numerical results are further compared to those from a conventional crystal plasticity model. It is shown that while the calculated lattice strains and lattice rotations from both models are in agreement with the measured ones, the non-local model provides a better estimation of localized stresses in the regions with a sharp strain gradient. This difference is more pronounced in the vicinity of twins, where the calculated stresses and geometrically necessary dislocation densities by the non-local model are in better agreement with the measurements.

Optical matter machines: angular momentum conversion by collective modes in optically bound nanoparticle arrays

The creation of optically powered self-assembling nano-to-meso-scale machines that do work is a long-standing goal in photonics. We demonstrate an optical matter (OM) machine that converts the spin angular momentum (SAM) of light into orbital angular momentum (OAM) to do mechanical work. The specific OM machine we study is based on a sixfold symmetric hexagonally ordered nanoparticle array that operates as an OM “gear” that is assembled and made to rotate in a circularly polarized Gaussian beam. The rotational symmetry of the OM gear leads to a selection rule for the allowed scattering modes based on their angular momentum. Electrodynamics calculations show that the collective scattering modes with the largest angular momentum scatter strongly in the transverse direction. Simulations and experiments show that the angular momentum that accompanies the scattered light causes a “negative torque” response on the OM gear and drives a “probe” particle placed outside the OM gear around the gear in an asymmetric force field analogously to Brownian ratchets. The gear–probe OM machine concept can be expanded to applications in nanofluidics and particle sorting.

Determining Attributes of Finite Fracture Networks in Low-Permeability Carbonate Reservoirs

SummaryCarbonate reservoirs usually consist of multiple units each with different degrees of layer-bound fracture density, height, length, and angular scatter. Some units may have finite fracture networks (FFNs), and some others may contain only isolated fractures. FFNs are islands of interconnected fractures within a sea of isolated fractures. The fracture volume can be estimated from the initial surge in production if a wellbore intersects only a single FFN. Combining with fracture density and aperture measurements from borehole images, FFN volume, drainage area, and other relevant attributes can be calculated. If, however, a slanted well intersects an unknown number of FFNs each in a different unit, it is not possible to estimate each FFN fracture volume from initial fracture production. Because the connectivity threshold for initiation of FFNs is not known or cannot be calculated, it is not possible to determine how many FFNs the borehole intersects. One way is to set an arbitrary threshold of fracture connectivity, λc.Based on this initial value, a fracture-flow model can be generated and adjusted until the inferred rate time and cumulative time curves converge to observed values. The adjustment is accomplished by changing the number of FFNs using different connectivity threshold λc and estimating their size by modifying unknown or uncertain parameters such as fracture aperture. The final model yields the mostly likely number and size of all FFNs and provides an approximate forecast for future production performance.The ability to match production performance without taking pressure into consideration shows that rate decrease in fractured reservoirs with FFNs is not only related to pressure drawdown but also, perhaps more importantly, to depletion of FFNs starting from the smallest size or the one with highest drainage efficiency.One drawback of the method is that different numbers of FFNs may have similar inferred production performance and cumulative production. This is an inevitable drawback inherent in most models that must rely on multiple uncertain or unknown parameters. The only way to decrease the range of possible solutions is to decrease the uncertainties in the underlying input parameters. In any case, alternative results may be presented as a range of possible solutions.

Measurements of neutron transport of well defined silicon filtered beam in lead

The correct description of neutron transport in lead is an essential task for correct description of tritium production in the DEMO (DEMOnstration Power Station) breeding blanket because some concepts deal with lead as a major component: namely the WCLL (water cooled lithium lead blanket), HCLL (helium cooled lithium lead blanket), and DCLL (dual cooled lithium lead blanket). Concerning the improvement of the knowledge about the transport of fast neutrons in lead, a set of experiments and calculations was carried out to study this problem with a well-defined neutron beam. The neutron flux behind various lead arrangements positioned along the beam axis was measured using a stilbene scintillation crystal (10 mm × 10 mm) with neutron and gamma pulse shape discrimination. The measurement was performed along the beam axis and in the case of the thick target also above the axis, to estimate the neutron angular scatter in lead. The calculations were realized using MCNP6 with various nuclear data libraries. Discrepancies in the angular distribution description in the energy region of about 1 MeV were discovered by these experiments.

Determination of microparticle characteristics in an etching plasma

The properties of one single melamine formaldehyde microparticle, levitated in the sheath of a low‐pressure radio frequency‐driven plasma, are determined with a novel procedure using in situ Mie scattering. By placing the measurement equipment inside the vacuum vessel, optical access is not limited to available viewports, and the complete scatter profile can be measured. The developed fitting routine uses peaks and valleys in the angular scatter profile to accurately determine the particle's refractive index, size, and plasma‐induced etch rate. In plasma at a pressure of 13 Pa operated at 10 W, obtained refractive indices of 1.657 ± 0.01 are close to those specified by the supplier, while the initial size (2.168 ± 0.007 μm) is relatively 8% off from the supplier‐specified value. With an estimated contamination of ambient air of 4 ± 1% in pristine Ar, etch rates of 1.9 ± 0.2 nm/min are measured.

Light scattering by magnons in whispering gallery mode cavities

Brillouin light scattering is an established technique to study magnons, the elementary excitations of a magnet. Its efficiency can be enhanced by cavities that concentrate the light intensity. Here, we theoretically study inelastic scattering of photons by a magnetic sphere that supports optical whispering gallery modes in a plane normal to the magnetization. Magnons with low angular momenta scatter the light in the forward direction with a pronounced asymmetry in the Stokes and the anti-Stokes scattering strength, consistent with earlier studies. Magnons with large angular momenta constitute Damon Eschbach modes are shown to inelastically reflect light. The reflection spectrum contains either a Stokes or anti-Stokes peak, depending on the direction of the magnetization, a selection rule that can be explained by the chirality of the Damon Eshbach magnons. The controllable energy transfer can be used to manage the thermodynamics of the magnet by light.

Scattering of low-energetic atoms and molecules from a boron-doped CVD diamond surface

Abstract For the detection of low energetic neutral atoms for the remote sensing of space plasmas, charge state conversion surfaces are used to ionize the neutrals for their subsequent measurement. We investigated a boron-doped Chemical Vapor Deposition (CVD) diamond sample for its suitability to serve as a conversion surface on future space missions, such as NASA’s Interstellar Mapping and Acceleration Probe. For H and O atoms incident on conversion surface with energies ranging from 195 to 1000 eV and impact angles from 6° to 15° we measured the angular scattering distributions and the ionization yields. Atomic force microscope and laser ablation ionization mass spectrometry analyses were applied to further characterize the sample. Based on a figure-of-merit, which included the ionization yield and angular scatter distribution, the B-doped CVD surface was compared to other, previously characterized conversion surfaces, including e.g. an undoped CVD diamond with a metallized backside. For particle energies below 390 eV the performance of the B-doped CVD conversion surfaces is comparable to surfaces studied before. For higher energies the figure-of-merit indicates a superior performance. From our studies we conclude that the B-doped CVD diamond sample is well suited for its application on future space missions.

Preferential spin canting in nanosize zinc ferrite

Zinc ferrite nanoparticles powder with average size of 10.0±0.5nm was synthesized by the citrate precursor route. We studied the structural and magnetic properties using X-ray diffraction, vibrating sample magnetometry and Mössbauer spectroscopy. X-ray diffraction patterns show that the synthesized zinc ferrite possesses good spinel structure. Both Mössbauer and magnetization data indicate superparamagnetic ferrimagnetic particles at room temperature. The magnetic behavior is determined by a considerable degree of cation inversion with FeIII in tetrahedral A-sites. Mössbauer spectroscopy at low temperature and in high applied magnetic field reveals that A-site spins are aligned antiparallel to the applied field with some possible angular scatter whereas practically all octahedral B-site spins are canted contrasting some earlier reported partial B-site spin canting in nanosize zinc ferrite. Deviations from the antiferromagnetic arrangement of B-site spins are supposed to be caused by magnetic frustration effects.

On image quality metrics and the usefulness of grids in digital mammography.

Antiscatter grids are used in digital mammography to reduce the scattered radiation from the breast and improve image contrast. They are, however, imperfect and lead to partial absorption of primary radiation, as well as failing to absorb all scattered radiation. Nevertheless, the general consensus has been that antiscatter grids improve image quality for the majority of breast types and sizes. There is, however, inconsistency in the literature, and recent results show that a substantial image quality improvement can be achieved even for thick breasts if the grid is disposed of. The purpose of this study was to investigate if differences in the considered imaging task and experimental setup could explain the different outcomes. We estimated the dose reduction that can be achieved if the grid were to be removed as a function of breast thickness with varying geometries and experimental conditions. Image quality was quantified by the signal-difference-to-noise ratio (SDNR) measured using an aluminum (Al) filter on blocks of poly(methyl methacrylate) (PMMA), and images were acquired with and without grid at a constant exposure. We also used a theoretical model validated with Monte Carlo simulations. Both theoretically and experimentally, the main finding was that when a large [Formula: see text] Al filter was used, the SDNR values for the gridless images were overestimated up to 25% compared to the values for the small [Formula: see text] filter, and gridless imaging was superior for any PMMA thickness. For the small Al filter, gridless imaging was only superior for PMMAs thinner than 4cm. This discrepancy can be explained by a different sensitivity to and sampling of the angular scatter spread function, depending on the size of the contrast object. The experimental differences were eliminated either by using a smaller region of interest close to the edge of the large filter or by applying a technique of scatter correction by subtracting the estimated scatter image. These results explain the different conclusions reported in the literature and show the importance of the selection of measurement methods. Since the interesting structures in mammography are below the 1-cm scale, we advocate the use of smaller contrast objects for assessment of antiscatter grid performance.

SU‐E‐T‐116: The Water Equivalence of Organic Liquid Scintillators for Proton Dosimetry

Organic liquid scintillators are currently under investigation for use in proton dosimetry. The purpose of this work is to evaluate the water equivalence of these materials as a preliminary step to identify scintillators that are well-suited to this purpose. Stopping powers were calculated for 0.001-1000 MeV protons in water, polystyrene, and two organic liquid scintillators: BC-531 and OptiPhase 'Hi-Safe' 3 at 0%, 25%, and 50% concentrations of water. Angular scatter was quantified by theta0, a characteristic multiple Coulomb scattering angle analogous to the standard deviation of a Gaussian distribution of proton angles relative to the incident beam axis. Theta0 was calculated as a function of depth over the range of 200 MeV protons in these materials. Collisional stopping power in BC-531 ranged from +44% to +1% ofthat in water. It remained within 6% from 2-600 MeV. OptiPhase ranged from +24% to -2%, with smaller deviations at increased water concentrations. At all concentrations, OptiPhase showed smaller deviations than polystyrene and BC-531 and remained within 1% of water from 2-600 MeV.Theta0 was very similar for all materials, with deviations from water of 5 milliradians or less over the majority of the proton range. BC-531 showed deviations of 10 milliradians or more in the last few millimeters of the range. OptiPhase showed smaller deviations than BC-531 or polystyrene, and these deviations decreased with increasing water concentration. OptiPhase was found to be more water equivalent than BC-531 or polystyrene in stopping power and angular scatter, and increased water concentration improved both quantities. Large deviations in stopping power were only found below 2 MeV for any material, where proton range is less than 0.1 millimeter. The deviations from water found in angular scatter were less significant, and probably too small to affect measurement.

Working against gravity: horizontal honeybee waggle runs have greater angular scatter than vertical waggle runs

The presence of noise in a communication system may be adaptive or may reflect unavoidable constraints. One communication system where these alternatives are debated is the honeybee (Apis mellifera) waggle dance. Successful foragers communicate resource locations to nest-mates by a dance comprising repeated units (waggle runs), which repetitively transmit the same distance and direction vector from the nest. Intra-dance waggle run variation occurs and has been hypothesized as a colony-level adaptation to direct recruits over an area rather than a single location. Alternatively, variation may simply be due to constraints on bees' abilities to orient waggle runs. Here, we ask whether the angle at which the bee dances on vertical comb influences waggle run variation. In particular, we determine whether horizontal dances, where gravity is not aligned with the waggle run orientation, are more variable in their directional component. We analysed 198 dances from foragers visiting natural resources and found support for our prediction. More horizontal dances have greater angular variation than dances performed close to vertical. However, there is no effect of waggle run angle on variation in the duration of waggle runs, which communicates distance. Our results weaken the hypothesis that variation is adaptive and provide novel support for the constraint hypothesis.

Two-parameter angular light scatter collection for microfluidic flow cytometry by unique waveguide structures

Waveguide numerical aperture restrictions and light-blocking elements are used to create a microfluidic cytometer with both illumination and two-parameter light scatter collection systems integrated on-chip. Good forward scatter coefficients of variation (9.7-18.3%) are achieved for polystyrene beads under a reasonably high flow rate (28 cm/s) using a greatly simplified optical system.

A paleomagnetic and rock-magnetic study of a neogene lava flow sequence in La Gomera (Canary Islands, Spain)

We present rock-magnetic and paleomagnetic results obtained on samples belonging to a Neogene sequence of 11 successive lava flows and a dyke from La Gomera (Canary Islands, Spain). Analysis of thermomagnetic curves allows to distinguish three types of samples: (i) Type H samples with low-Ti titanomagnetite as the only carrier of remanence; (ii) type M samples with a main intermediate Curie-temperature phase (TC = 450°C) and low-Ti titanomagnetite; (iii) type L curves with a low Curie-temperature phase (TC = 120 to 200°C) and an intermediate Curie-temperature phase (TC = 400°C). Analysis of hysteresis parameters suggests that the grain size of most studied samples corresponds to pseudo single-domain particles, which can be also interpreted as a mixture of single-domain and multi-domain particles. Paleomagnetic experiments reveal only a single paleomagnetic component. Characteristic remanence of all studied lava flows and the dyke shows reverse polarity. The mean direction of the whole sequence is D = 188.2°, I =−35.4° (k = 46.9; α95 = 6.4°) and the calculated paleomagnetic pole yields a longitude λ= 150.7° and a latitude ϕ= 78.8° (k = 59.4; A95 = 5.7°). Secular variation is analysed through the scatter of virtual geomagnetic poles (VGP). A VGP angular scatter SB = 5.9 with an upper confidence limit Sup = 8.0 and a lower confidence limit Slow = 4.6 are obtained. This scatter is clearly smaller than the average for this latitude obtained for the last 5 Ma. The studied lava flows were probably emitted in a relatively short time interval.