Search NASA⌕ Search

SEARCH · Search NASA

Results for “MULTIPLE SCATTERING”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,333 records · Page 74
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Quality assurance of proton beams using a multilayer ionization chamber system

Purpose: The measurement of percentage depth-dose (PDD) distributions for the quality assurance of clinical proton beams is most commonly performed with a computerized water tank dosimetry system with ionization chamber, commonly referred to as water tank. Although the accuracy and reproducibility of this method is well established, it can be time-consuming if a large number of measurements are required. In this work the authors evaluate the linearity, reproducibility, sensitivity to field size, accuracy, and time-savings of another system: the Zebra, a multilayer ionization chamber system.Methods: The Zebra, consisting of 180 parallel-plate ionization chambers with 2 mm resolution, was used to measure depth-dose distributions. The measurements were performed for scattered and scanned proton pencil beams of multiple energies delivered by the Hitachi PROBEAT synchrotron-based delivery system. For scattered beams, the Zebra-measured depth-dose distributions were compared with those measured with the water tank. The principal descriptors extracted for comparisons were: range, the depth of the distal 90% dose; spread-out Bragg peak (SOBP) length, the region between the proximal 95% and distal 90% dose; and distal-dose fall off (DDF), the region between the distal 80% and 20% dose. For scanned beams, the Zebra-measured ranges were compared with those acquired using a Bragg peak chamber during commissioning.Results: The Zebra demonstrated better than 1% reproducibility and monitor unit linearity. The response of the Zebra was found to be sensitive to radiation field sizes greater than 12.5 × 12.5 cm; hence, the measurements used to determine accuracy were performed using a field size of 10 × 10 cm. For the scattered proton beams, PDD distributions showed 1.5% agreement within the SOBP, and 3.8% outside. Range values agreed within −0.1 ± 0.4 mm, with a maximum deviation of 1.2 mm. SOBP length values agreed within 0 ± 2 mm, with a maximum deviation of 6 mm. DDF values agreed within 0.3 ± 0.1 mm, with a maximum deviation of 0.6 mm. For the scanned proton pencil beams, Zebra and Bragg peak chamber range values demonstrated agreement of 0.0 ± 0.3 mm with a maximum deviation of 1.3 mm. The setup and measurement time for all Zebra measurements was 3 and 20 times less, respectively, compared to the water tank measurements.Conclusions: Our investigation shows that the Zebra can be useful not only for fast but also for accurate measurements of the depth-dose distributions of both scattered and scanned proton beams. The analysis of a large set of measurements shows that the commonly assessed beam quality parameters obtained with the Zebra are within the acceptable variations specified by the manufacturer for our delivery system.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2026

Simplified spin dependence in dark matter direct detection

The interactions of dark matter with Standard Model particles can be systematically studied in the language of effective field theories. We investigate dark matter interactions with Standard Model particles, including spin-dependent interactions, for direct detection experiments and demonstrate that, although the scattering rate generally depends on multiple types of material response functions, certain linear combinations of these material response functions vanish if the initial and final electronic states share the same Hamiltonian. We also find that several other response functions vanish in parity-symmetric materials, making these systems as simple as isotropic detectors in some respects. Finally, we present the scattering rate for an anisotropic, possibly chiral detector, for generic dark matter-electron spin interactions. These relations reduce the number of independent response functions needed, thereby simplifying the computational complexity for a broad class of dark matter models. Our results provide a complete and efficient toolkit for analyzing electron recoil signals in diverse detector materials.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

A CRITICAL ASSESSMENT OF PHOTOMETRIC REDSHIFT METHODS: A CANDELS INVESTIGATION

We present results from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) photometric redshift methods investigation. In this investigation, the results from 11 participants, each using a different combination of photometric redshift code, template spectral energy distributions (SEDs), and priors, are used to examine the properties of photometric redshifts applied to deep fields with broadband multi-wavelength coverage. The photometry used includes U-band through mid-infrared filters and was derived using the TFIT method. Comparing the results, we find that there is no particular code or set of template SEDs that results in significantly better photometric redshifts compared to others. However, we find that codes producing the lowest scatter and outlier fraction utilize a training sample to optimize photometric redshifts by adding zero-point offsets, template adjusting, or adding extra smoothing errors. These results therefore stress the importance of the training procedure. We find a strong dependence of the photometric redshift accuracy on the signal-to-noise ratio of the photometry. On the other hand, we find a weak dependence of the photometric redshift scatter with redshift and galaxy color. We find that most photometric redshift codes quote redshift errors (e.g., 68% confidence intervals) that are too small compared to that expected from the spectroscopic control sample. We find that all codes show a statistically significant bias in the photometric redshifts. However, the bias is in all cases smaller than the scatter; the latter therefore dominates the errors. Finally, we find that combining results from multiple codes significantly decreases the photometric redshift scatter and outlier fraction. We discuss different ways of combining data to produce accurate photometric redshifts and error estimates.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Charged hadron multiplicities at the HERMES experiment

The HERMES collaboration has measured charge-separated pion and kaon multiplicities in semi-inclusive deep inelastic scattering using a 27.6 GeV electron or positron beam scattering off a hydrogen or deuterium target. The results are presented as a function of the Bjorken variable x {sub B }, the negative squared four-momentum transfer Q {sup 2}, the hadron fractional energy z and it’s transverse momentum P {sub h ⊥}. These data will be very useful to understand the quark-fragmentation process in deep-inelastic hadron electro-production and will serve as crucial input in the understanding of spin asymmetries in polarized semi-inclusive deep-inelastic scattering.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Study of the energy dependence of the underlying event in proton-antiproton collisions

We study charged particle production (p(T) > 0.5 GeV/c, vertical bar eta vertical bar < 0.8) in proton-antiproton collisions at total center-of-mass energies root s = 300 GeV, 900 GeV, and 1.96 TeV. We use the direction of the charged particle with the largest transverse momentum in each event to define three regions of eta - phi space: "toward", "away", and "transverse." The average number and the average scalar pT sum of charged particles in the transverse region are sensitive to the modeling of the "underlying event." The transverse region is divided into a MAX and MIN transverse region, which helps separate the "hard component" (initial and final-state radiation) from the "beam-beam remnant" and multiple parton interaction components of the scattering. The center-of-mass energy dependence of the various components of the event is studied in detail. The data presented here can be used to constrain and improve QCD Monte Carlo models, resulting in more precise predictions at the LHC energies of 13 and 14 TeV.

Aaltonen, T.↗
DOE OSTI2021

Modeling of the Molten Salt Reactor Experiment with SCALE

A SCALE model was developed for the Molten Salt Reactor Experiment (MSRE) benchmark that was recently added to the International Handbook of Evaluated Reactor Physics Benchmark Experiments. This SCALE model served as a basis for criticality calculations and nuclear data sensitivity and uncertainty analyses with the Monte Carlo code Shift and the TSUNAMI computational capabilities in the SCALE code system. The focus of this work is the assessment of the impact of nuclear data on the calculated eigenvalue results in support of the discussion of differences between the calculated and the experimental eigenvalue result. The differences in the eigenvalues obtained using the ENDF/B-VII.0, ENDF/B-VII.1, and ENDF/B-VIII.0 nuclear data libraries cover a relatively small range of ~230 pcm. Since eigenvalue sensitivity of the MSRE is dominated by the neutron multiplicity and neutron capture of 235 U and elastic scattering in graphite, relevant changes in the ENDF/B libraries for nuclear reactions (such as carbon capture) that caused large differences in other graphite-moderated systems did not have a significant impact. Propagation of nuclear data uncertainty results in an eigenvalue uncertainty of ~700 pcm with the major contributors being 235 U neutron multiplicity, graphite elastic scattering, and 7Li neutron capture. All calculations resulted in large differences of ~2000 pcm in eigenvalue compared to the benchmark experimental value. Several potential contributors to this difference—including uncertainties and gaps in the knowledge of the material, geometry, and nuclear data—were identified. Simplified models of the full MSRE core were developed, and similarity assessments were conduced with the full MSRE core model. It was found that simplified models can serve as adequate surrogates of the full-core model such that they can be used for performing selected nuclear data performance assessments with a lower computational burden.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2014

TH-C-19A-01: Analytic Design Method to Make a 2D Planar, Segmented Ion Chamber Water-Equivalent for Proton Dose Measurements

Purpose: Quality Assurance (QA) measurements of proton therapy fields must accurately measure steep longitudinal dose gradients as well as characterize the dose distribution laterally. Currently, available devices for two-dimensional field measurements perturb the dose distribution such that routine QA measurements performed at multiple depths require multiple field deliveries and are time consuming. Methods: A design procedure for a two-dimensional detector array is introduced whereby the proton energy loss and scatter are adjusted so that the downstream dose distribution is maintained to be equivalent to that which would occur in uniform water. Starting with the design for an existing, functional two-dimensional segmented ion chamber prototype, a compensating material is introduced downstream of the detector to simultaneously equate the energy loss and lateral scatter in the detector assembly to the values in water. An analytic formalism and procedure is demonstrated to calculate the properties of the compensating material in the general case of multiple layers of arbitrary material. The resulting design is validated with Monte Carlo simulations. Results: With respect to the specific prototype design considered, the results indicate that a graphite compensating layer of the proper dimensions can yield proton beam range perturbation less than 0.1mm and beam sigma perturbation less than 2% across the energy range of therapeutic proton beams. Conclusion: We have shown that, for a 2D gas-filled detector array, a graphite-compensating layer can balance the energy loss and multiple Coulomb scattering relative to uniform water. We have demonstrated an analytic formalism and procedure to determine a compensating material in the general case of multiple layers of arbitrary material. This work was supported by the US Army Medical Research and Materiel Command under Contract Agreement No. DAMD17-W81XWH-04-2-0022. Opinions, interpretations, conclusions and recommendations are those of the author and are not necessarily endorsed by the US Army.

07 ISOTOPE AND RADIATION SOURCES↗
NASA NTRS1984

Ratioed scatter diagrams - An erotetic method for phase identification on complex surfaces using scanning Auger microscopy

By ratioing multiple Auger intensities and plotting a two-dimensional occupational scatter diagram while digitally scanning across an area, the number and elemental association of surface phases can be determined. This can prove a useful tool in scanning Auger microscopic analysis of complex materials. The technique is illustrated by results from an anomalous region on the reaction zone of a SiC/Ti-6Al-4V metal matrix composite material. The anomalous region is shown to be a single phase associated with sulphur and phosphorus impurities. Imaging of a selected phase from the ratioed scatter diagram is possible and may be a useful technique for presenting multiple scanning Auger images.

Browning, R.↗
DOE OSTI2014

Diagnosing collisions of magnetized, high energy density plasma flows using a combination of collective Thomson scattering, Faraday rotation, and interferometry (invited)

A suite of laser based diagnostics is used to study interactions of magnetised, supersonic, radiatively cooled plasma flows produced using the Magpie pulse power generator (1.4 MA, 240 ns rise time). Collective optical Thomson scattering measures the time-resolved local flow velocity and temperature across 7–14 spatial positions. The scattering spectrum is recorded from multiple directions, allowing more accurate reconstruction of the flow velocity vectors. The areal electron density is measured using 2D interferometry; optimisation and analysis are discussed. The Faraday rotation diagnostic, operating at 1053 nm, measures the magnetic field distribution in the plasma. Measurements obtained simultaneously by these diagnostics are used to constrain analysis, increasing the accuracy of interpretation.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS2008

Interferometric Rayleigh Scattering Measurement System

A method and apparatus for performing simultaneous multi-point measurements of multiple velocity components in a gas flow is described. Pulses of laser light are directed to a measurement region of unseeded gas to produce Rayleigh or Mie scattered light in a plurality of directions. The Rayleigh or Mie scattered light is collected from multiple directions and combined in a single collimated light beam. The Rayleigh or Mie scattered light is then mixed together with a reference laser light before it is passed through a single planar Fabry-Perot interferometer for spectral analysis. At the output of the interferometer, a high-sensitivity CCD camera images the interference fringe pattern. This pattern contains the spectral and spatial information from both the Rayleigh scattered light and the reference laser light. Interferogram processing software extracts and analyzes spectral profiles to determine the velocity components of the gas flow at multiple points in the measurement region. The Rayleigh light rejected by the interferometer is recirculated to increase the accuracy and the applicability of the method for measurements at high temperatures without requiring an increase in the laser energy.

Bivolaru, Daniel↗
DOE OSTI2018

Decoupling carrier concentration and electron-phonon coupling in oxide heterostructures observed with resonant inelastic x-ray scattering

In this paper, we report the observation of multiple phonon satellite features in ultra thin superlattices of form n SrIrO 3 / m SrTiO 3 using resonant inelastic x-ray scattering. As the values of n and m vary the energy loss spectra show a systematic evolution in the relative intensity of the phonon satellites. Using a closed-form solution for the RIXS cross section, we extract the variation in the electron-phonon coupling strength as a function of n and m . Combined with the negligible carrier doping into the SrTiO 3 layers, these results indicate that tuning of the electron-phonon coupling can be effectively decoupled from doping. In conclusion, this work showcases both a feasible method to extract the electron-phonon coupling in superlattices and unveils a potential route for tuning this coupling which is often associated with superconductivity in SrTiO 3 -based systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Super-resonant four-photon collinear laser frequency multiplication in plasma

Resonant four-photon scattering could nearly double frequencies of intense laser pulses in plasma. However, transverse slippage between pulses presents a technological challenge, while collinear four-photon scattering is forbidden for classical light dispersion in plasma. Nonlinear renormalization of intense laser pulses can enable collinear four-photon resonance. However, such a very intensity-sensitive resonance is difficult to maintain for evolving pulses. Remarkably, there is a lower-dimensionality submanifold of the resonant four-photon manifold where the evolving pulses stay in resonance. Furthermore this could enable an all-optical frequency doubling of mildly relativistic-intense laser pulses in collinear geometry, advantageously free of the transverse slippage challenges.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Concurrent determination of nanocrystal shape and amorphous phases in complex materials by diffraction scattering computed tomography

Advanced functional materials often contain multiple phases which are (nano)crystalline and/or amorphous. The spatial distribution of these phases and their properties, including nanocrystallite size and shape, often drives material function yet is difficult to obtain with current experimental techniques. This article describes the use of diffraction scattering computed tomography, which maps wide-angle scattering information onto sample space, to address this challenge. The wide-angle scattering signal contains information on both (nano)crystalline and amorphous phases. Rietveld refinement of reconstructed diffraction patterns is employed to determine anisotropic nanocrystal shapes. The background signal from refinements is used to identify contributing amorphous phases through multivariate curve resolution. Thus it is demonstrated that reciprocal space analysis in combination with diffraction scattering computed tomography is a very powerful tool for the complete analysis of complex multiphase materials such as energy devices.

Birkbak, Mie Elholm↗
DOE OSTI2017

The asymptotic behaviour of the scattering matrix in a neighbourhood of the endpoints of a spectral gap

The behaviour of the scattering matrix is investigated as the spectral parameter approaches an endpoint of a spectral gap of a quantum waveguide from the inside or the outside. The waveguide has two sleeves, one is cylindrical and the other periodic. When the spectral parameter traverses the spectral gap, the scattering matrix is reshaped because the number of waves inside and outside the gap is different. Notwithstanding, the smaller scattering matrix (in size) is transformed continuously into an identical block in the bigger scattering matrix and, in addition, the latter takes block diagonal form in the limit at the endpoint of the gap, that is, at the spectral threshold. The unexpected phenomena are related to the other block. It is shown that in the limit this block can only take certain values at the threshold, and taking one or other of these values depends on the structure of the continuous spectrum and also on the structure of the subspace of 'almost standing' waves at the threshold, which are solutions of the homogeneous problem that transfer no energy to infinity. A criterion for the existence of such solutions links the dimension of this subspace to the multiplicity of the eigenvalue −1 of the threshold scattering matrix. Asymptotic formulae are obtained, which show, in particular, that the phenomenon of anomalous scattering of high-amplitude waves at near-threshold frequencies, discovered by Weinstein in a special acoustic problem, also occurs in periodic waveguides. Bibliography: 38 titles. (paper)

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2015

Multiple Fano interferences in a plasmonic metamolecule consisting of asymmetric metallic nanodimers

We theoretically explore signatures of plasmonic Fano interferences in a subwavelength plasmonic metamolecule consisting of closely packed asymmetric gold nanodimers, which lead to the possibility of generating multiple Fano resonances in the scattering spectrum. This spectral feature is attributed to the interference between bright and dark plasmonic modes sustained by the constituent nanodimers. The excited Fano dips are highly sensitive in both wavelength and amplitude to geometry and background dielectric medium. The tunability of induced Fano resonances associated with enhanced electric fields from the visible to infrared region provides promising applications, particularly in refractive index sensing, light-trapping, and photon up-converting.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Current-enabled optical conductivity of superconductors

In most superconductors, optical excitations require impurity scattering or the presence of multiple bands. This is because in clean single-band superconductors, the combination of particle-hole and inversion symmetries prevents momentum-conserving transitions. In this Letter we show how the flow of supercurrent can lead to new contributions to optical conductivity. As the supercurrent breaks inversion symmetry, transitions across the superconducting gap become allowed even in clean superconductors and dominate over impurity-induced contributions for energies comparable to the gap width. Further, the response is dependent on the nature of the underlying normal state as well as on the type of superconducting order. Use of an external magnetic field to produce a screening supercurrent with controllable magnitude and direction, enables a detailed investigation of the superconducting state, allowing determination of the gap symmetry in unconventional superconductors for which other techniques have not been practicable.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Nonstationary Spatial Energy Distribution of a Cascade of Knock-out Atoms in a Solid

We consider the evolution of a cascade of atomic collisions in a solid consisting of identical atoms. The solution to the Boltzmann kinetic equation describing a nonstationary spatial energy distribution of slowing down atoms is obtained considering their multiplication. We assume that the scattering of atoms is elastic and spherically symmetric in the center-of-mass system and that the scattering cross section is constant. Some particular cases of this solution coincide with the results obtained earlier.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

First Search for the EMC Effect and Nuclear Shadowing in Neutrino Nucleus Deep Inelastic Scattering at MINERvA

Decades of research in electron-nucleus deep inelastic scattering (DIS) have provided a clear picture of nuclear physics at high momentum transfer. While these effects have been clearly demonstrated by experiment, the theoretical explanation of their origin in some kinematic regions has been lacking. Particularly, the effects in the intermediate regions of Bjorken-x, anti-shadowing and the EMC effect have no universally accepted quantum mechanical explanation. In addition, these effects have not been measured systematically with neutrino-nucleus deep inelastic scattering, due to experiments lacking multiple heavy targets.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗