Coherent Scattering Cross Section Research Articles

Re-Analysis of Recent Neutron Diffusion and Transmission Measurements in Nuclear Graphite

We revisit the determination by Bowman et al. of unusual neutron transport characteristics for a newly fabricated form of graphite [Nucl. Sci. Eng., 159, 182 (2008); Nucl. Sci. Eng., 161, 68 (2009)]. From MCNP modeling and consideration of data from other experiments, we determine revised values for the neutron transport parameters of this graphite. Our reanalysis gives a coherent scattering cross section σcoh ˜ 4 b at 50 meV, a small-angle neutron scattering cross section σsans ˜ 11 to 13 b at 1 meV, and an effective capture cross section σa = 5.8 ± 0.5 mb. Scaled to a graphite reference density of 1.60 g/cm3, we find a diffusion coefficient D̄ = 0.94 ± 0.03 cm and a diffusion length L = 47.7 ± 3.7 cm. Apart from the somewhat larger values of σa and D̄, these are not untypical parameters for graphite. Based on our investigation, the recent experiments and analysis of Bowman et al. do not give evidence for different transport properties for this newly fabricated graphite.

Neutrino backgrounds to dark matter searches and directionality

Neutrino-nucleus coherent scattering cross sections can be as large as 10−39 cm2, while current dark matter experiments have sensitivities to WIMP coherent scattering cross sections several orders of magnitude smaller. With large target masses and few κeV recoil energy detection thresholds, coherent scattering of solar neutrinos becomes an irreducible background. Directional dark matter detection can discriminate against such backgrounds in a second observable: nuclear recoil angle. The motion of our solar system around the galactic center should produce an apparent dark matter wind. With this signal, directional detection of dark matter can provide an unambiguous observation of dark matter interactions even in the presence of backgrounds, from neutrinos and other sources. The DM-TPC collaboration and others are developing recoil direction-sensitive dark matter detectors with very promising results.

Neutrino backgrounds to dark matter searches

Neutrino coherent scattering cross sections can be as large as ${10}^{\ensuremath{-}39}\text{ }\text{ }{\mathrm{cm}}^{2}$, while current dark matter experiments have sensitivities to WIMP coherent scattering cross sections 5 orders of magnitude smaller; future experiments plan to have sensitivities to cross sections as small as ${10}^{\ensuremath{-}48}\text{ }\text{ }{\mathrm{cm}}^{2}$. With large target masses and few keV recoil energy detection thresholds, neutral current coherent scattering of solar neutrinos becomes an irreducible background in dark matter searches. In the current zero-background analysis paradigm, neutrino coherent scattering will limit the achievable sensitivity to dark matter scattering cross sections, at the level of ${10}^{\ensuremath{-}46}\text{ }\text{ }{\mathrm{cm}}^{2}$.

Dynamical structure factor of a nonlinear Klein-Gordon lattice

The quantum modes of a nonlinear Klein-Gordon lattice have been computed numerically [L. Proville, Phys. Rev. B 71, 104306 (2005)]. The on-site nonlinearity has been found to lead to phonon bound states. In the present paper, we compute numerically the dynamical structure factor so as to simulate the coherent scattering cross section at low temperature. The inelastic contribution is studied as a function of the on-site anharmonicity. Interestingly, our numerical method is not limited to the weak anharmonicity and permits one to study thoroughly the spectra of nonlinear phonons.

Coherent scattering X-ray imaging at the Brazilian National Synchrotron Laboratory: Preliminary breast images

The angular distribution of coherent scatter (low-momentum transfer) carries information about atomic structures, resulting in a pattern, which can be used to reconstruct a series of images. Coherent-scatter computed tomography is a novel imaging method developed to produce cross-sectional images based on the X-ray diffraction properties of an object. A different approach to coherent X-ray imaging is possible by fixing the detector at a given scatter angle θ , which produces an interference peak and then, carried out a tomography in the standard way. The cross-sectional images obtained allow determining the spatial dependence of coherent scatter cross-section of selected volume elements of inhomogeneous, extend objects for a single predetermined value of θ of interest, leading to a simplification of the data processing and the complexity of the apparatus. This work presents preliminary coherent scattering images carried out at the X-ray Diffraction beamline of the National Synchrotron Light Laboratory in Campinas, Brazil. The specimens were excised human breast tissues fixed in formaline. No frozen procedure was used in order to minimize preferred orientation during sample preparation. About 1 mm thick slices cut from each of the fresh samples were mounted in frames without windows and placed on a translator to allow acquisition of scattering spectra. Cylinders containing healthy and cancerous (infiltrating ductal carcinoma) breast tissues were imagined at the characteristic angle for adipose tissue. Transmission and coherent scatter images are compared.

Neutron scattering study of the H-bond network in amorphous N-methylformamide

Original investigations of structural properties in noncrystalline solid N-methylformamide (HCONHCH(3)) are presented in this paper. After description of the sample preparation, the elastic neutron scattering formalism is applied to deduce the coherent scattering cross section for amorphous N-methylformamide. The contribution of each possible monomer (cis or trans) is computed and the corresponding distinct structure factor is deduced. Our measurements clearly show that the hydrogen-bond network occurs in amorphous N-methylformamide between C=O and N-H groups. The experimental spectra are consistent with an open-chain structure similar to the one existing in the crystalline form. The more probable clusters that have been identified in the liquid are also examined.

EXPERIMENTAL STUDY ON COHERENT SCATTERING OF 59.54 keV GAMMA RAYS BY Ag, In, AND Sn

The differential coherent scattering cross sections of 59.54 keV γ-rays in Ag, In, and Sn were experimentally determined at different angles, ranging from 40° to 135°, by the earlier method of Simsek. The measured cross sections were compared with the experimental values in the literature and with the numerically calculated results using S-matrix theory for available cases. Form factors at the momentum transfer 1.644≤ x ≤4.442 Å−1 were extracted from the measured cross sections. The results are discussed in the light of the predictions of form factor formalisms.

Dynamical molecular disorder and diffuse scattering in an alkane/urea incommensurate inclusion compound

The diffraction pattern of n-alkane/urea inclusion compounds is known to contain a broad diffuse scattering related to the molecular form factor of the alkane species, indicating individual rotational and/or translational disorder of these molecules. Inelastic coherent neutron scattering reveals for the first time the entirely dynamical character of the alkane molecular disorder around room temperature. This observation fully agrees with a recent model of the coherent scattering cross section of totally uncorrelated motions. In the ordered phase this diffuse scattering remains, but elastic, and very low energy molecular vibrational modes are evidenced. These observations are discussed in relation with previous incoherent neutron scattering results.

Implementation of an analyser crystal method for x-ray diffractiontomography

In this paper we present an experimental method which is well suited tosynchrotron x-ray diffraction tomography. The experimental technique utilizesan analyser crystal placed in the diffracted x-ray beam to selectively detectdiffracted photons at the desired scattering angle. This arrangement selectsthe prominent diffraction feature of a specimen component, allowing thespatial distribution of that component to be specifically and quantitativelyimaged. Images of the spatial variation of the differential x-ray scatteringcross section (reflectivity) in a cross sectional plane of interest arereconstructed using an iterative algebraic technique and an error functionalminimization. Reconstructed images of a well characterized phantom show thatmaterial features can be clearly delineated. Images based on the spatialvariation of x-ray linear attenuation coefficients and differential coherentscattering cross sections have been reconstructed with approximately 125 µmspatial resolution in the imaging plane.

Coherent X-ray scatter imaging and its applications in biomedical science and industry

Coherent x-ray scatter (CXRS) imaging refers to the spatially-resolved measurement of the coherent scatter cross-section in localised volume elements (“voxels”) of an extended object. Following a historical introduction to the subject of CXRS, an account is given of the physical principles on which it is based. Representative coherent scatter plots of materials of interest in medical and industrial applications are presented. Several alternative measurement configurations based on angular-dispersive and energy-dispersive x-ray diffraction are described and reasons are discussed which have lead to the adoption of the latter in the bulk of published CXRS investigations. The coherent scatter signal is subject to various degrading effects, such as self-attenuation of the primary and scatter radiations within the object, multiple scatter and statistical (photon) noise. These effects are described and data processing procedures to account for them in order to derive useful quantitative are illustrated. The design of a CXRS device (“RayScan”) in use at the Philips Research Labs is discussed in some detail and representative results obtained with it are presented. The utility of coherent scatter imaging is demonstrated with examples drawn from the fields of tissue characterization in the medical environment, explosives detection for airport security screening purposes and the detection of narcotics.

Efficient object scatter correction algorithm for third and fourth generation CT scanners

X-ray photons which are scattered inside the object slice and reach the detector array increase the detected signal and produce image artifacts as "cupping" effects in large objects and dark bands between regions of high attenuation. The artifact amplitudes increase with scanned volume or slice width. Object scatter can be reduced in third generation computed tomography (CT) geometry by collimating the detector elements. However, a correction can still improve image quality. For fourth generation CT geometry, only poor anti-scatter collimation is possible and a numeric correction is necessary. This paper presents a correction algorithm which can be parameterized for third and fourth generation CT geometry. The method requires low computational effort and allows flexible application to different body regions by simple parameter adjustments. The object scatter intensity which is subtracted from the measured signal is calculated with convolution of the weighted and windowed projection data with a spatially invariant "scatter convolution function". The scatter convolution function is approximated for the desired scanner geometry from pencil beam simulations and measurements using coherent and incoherent differential scatter cross section data. Several examples of phantom and medical objects scanned with third and fourth generation CT systems are discussed. In third generation scanners, scatter artifacts are effectively corrected. For fourth generation geometry with poor anti-scatter collimation, object scatter artifacts are strongly reduced.

Photon-atom scattering of 13.95-, 17.75-, 26.36-, and 59.54-keV photons by Cu, Zn, Zr, Nb, Mo, Ag, Cd, In, Sn, Ta, and W

Differential coherent scattering cross sections for 11 moderate- to high-atomic-number elements have been experimentally determined with $O$(10%) error at the photon energies 13.95, 17.75, 26.36, and 59.54 keV, corresponding to major photon-emission intensities of the radionuclide ${}^{241}\mathrm{Am}.$ The measurements were performed using a standard backscattering geometry setup to obtain scattering angles of 145\ifmmode^\circ\else\textdegree\fi{}, 154\ifmmode^\circ\else\textdegree\fi{}, and 165\ifmmode^\circ\else\textdegree\fi{}, with resulting photon momentum transfers in the range $1.07<~x<~4.76{\mathrm{\AA{}}}^{\mathrm{\ensuremath{-}}1}.$ High-purity (better than 99%) foils of Cu, Zn, Zr, Nb, Mo, Ag, Cd, In, Sn, Ta, and W were used as targets. A hyperpure germanium detector completed the arrangement. Measurements for Mo and Zr using the 17.75-keV photon-energy emission of ${}^{241}\mathrm{Am}$ were not possible due to the fact that for these targets at this photon energy, intense fluorescence overlapped significantly with the coherent scatter. At 26.36 keV the coherent scatter from Cd was similarly dominated by fluorescence. Experimental data have been compared with predictions from relativistic form factors (RFFs), modified relativistic form factors (MRFFs), and counterpart RFF and MRFF approximations with anomalous corrections using angle-independent scattering factors.

Measurements of anomalous elastic scattering of 59.54-keV photons.

Coherent scattering cross sections of 59.54-keV photons on target foils of {sup 64}Gd, {sup 66}Dy, {sup 68}Er, {sup 70}Yb, {sup 72}Hf, and {sup 73}Ta at 60{degree}, 90{degree}, and 120{degree} have been measured to provide information on the region of {ital K} anomalous elastic scattering. The results are compared with the values calculated by the second perturbative order {ital S} matrix and by two procedures based on the form-factor approximation corrected by the anomalous scattering factors. Agreement of the {ital S} matrix values is very satisfactory, on the whole, and that of the values given by the form-factor approximations is fairly good. {copyright} {ital 1996 The American Physical Society.}

Rayleigh and Compton scattering cross sections for low, medium and high Z elements in the energy region 23.18 ⩽ E ⩽ 30.85 keV

Using nearly monoenergetic unpolarised Kα x-ray photons coherent (Rayleigh) and incoherent (atomic Compton) scattering cross sections in the atomic region 13 ⩽ Z ⩽ 82 have been measured at 23.18, 24.14, 25.19, 26.27 and 30.85 keV. Experimental scattering cross sections in the momentum transfer region 1.322 h Å−1 ⩽ q ⩽ 1.759 h Å−1 [q = sin (θ/2)λ(Å)] were obtained at an angle of 90°. Experimental coherent scattering cross sections are in good agreement with second order S-matrix calculations, compared to theoretical estimates based on form factor approximations. Experimental incoherent scattering cross sections are higher than the theoretical estimates calculated using non-relativistic incoherent scattering functions for low and medium Z elements and lower for heavy elements. The latter is due to the binding effects at low photon energies.

Angular‐dependent coherent scatter measured with a diagnostic x‐ray image intensifier‐based imaging system

Low-angle scatter of x rays at diagnostic energies is primarily coherent. This coherence gives rise to interference effects resulting in x-ray diffraction patterns that are characteristic of the scattering material. A method is described of imaging these low-angle (0 degree-10 degrees) x-ray diffraction properties of tissue specimens using a diagnostic x-ray beam and image intensifier-based system. The coherent-scatter cross sections of several materials measured this way are presented. It is shown theoretically that the measurements made with this system can be expressed as the mono-energetic cross section "blurred" by the x-ray spectrum using a linear superposition integral. Experimental results using aluminum powder confirm this. Using a 70 kVp x-ray beam filtered with gadolinium to reduce the spectral width, materials such as water, Lucite, and hydroxyapatite all have significantly different diffraction patterns. The cross sections determined from this analysis from the basis of a unique method of characterizing and identifying tissue samples according to their atomic structure rather than x-ray attenuation properties.

Rayleigh scattering of 16.58 keV photons in the atomic region 59 ⩽ Z ⩽ 82 at q = 0.9457 h Å−1

Coherent scattering cross sections for the elements Pr, Sm, Gd, Dy, Ho, Er Pt, Au and Pb have been measured at the excitation energy 16.58 keV. The measured cross sections are compared with the normalised integrated scattering cross section values calculated using relativistic, non-relativistic and relativistic modified form factors. Atomic form factors are extracted from the measured cross sections at q = 0.9457 h Å−1. The results were compared with the different formalisms of form factor theory and their validity at q = 0.9457 h Å−1 is thoroughly discussed.

Elastic and compton scattering cross sections in the atomic region 12 ⩽ Z ⩽ 82

Coherent and Compton scattering cross sections for the elements Mg, Al, Mn, Ni, Cu, Y, Mod, Pd, Ag, Cd, In, Sn, Sb, Au and Pb have been measured at 32.06 keV (Ba Kα) and 33.29 keV (La Kα) x-ray energies. Measurements have been performed using an x-ray tube with a secondary excitor system as the excitation source instead of radioisotopes. In order to improve the efficiency of the detection system the excitation source detector and the sample assembly were placed in a vacuum chamber and a pressure of 10 −2 mbar was maintained throughout the measurements. The present system reduced the scattering and background effects considerably and improved the monochromaticity. Experimental coherent scattering cross sections are compared with the normalised integrated coherent scattering cross sections. Experimental results are higher around the edges indicating the oscillatory nature of coherent intensity, resonance behaviour and fine structure effects. Experimental incoherent scattering cross sections are higher than the theoretical estimates for low medium Z elements and lower for heavy elements. The latter is due to the effect of electron binding at low photon energies for heavy elements.

Coherent and incoherent scattering of low-energy X-ray photons in the atomic region 13 ≤ Z ≤ 82

Coherent- and incoherent-scattering cross sections for the elements Al, Cu, Y, In, Au, and Pb were measured using nearly monoenergetic unpolarized 35.86 and 39.96 keV X-ray beams with high-resolution Si (Li) detectors. Bremsstrahlung radiation from an X-ray tube was used to excite nearly monoenergetic X-rays in secondary targets. To improve the efficiency of the detection system the excitation source, detector, and the target assembly were placed in a vacuum chamber and a pressure of 10−2 mbar was maintained throughout the measurements. This system considerably reduced the background and scattering effects and improved the monochromacy. Experimental coherent-scattering cross sections are compared with the normalized integrated coherent-scattering cross sections calculated using the relativistic, nonrelativistic, and relativistic-modified form factors. Experimental incoherent-scattering cross sections are compared with the theoretical values, calculated using the nonrelativistic incoherent-scattering function. Good correspondence is observed between experimental and theoretical values in the given energy region.

Aggregation Phenomena of Model PS/PI Super-H-Shaped Block Copolymers. Influence of the Architecture

The super-H-shaped block copolymers belong to a new class of polymeric materials, the miktoarm stars (mikto from the Greek word μικτος meaning mixed), which includes star-shaped polymers in which from one or more junction points radiate different arms. Schematically, the super-H structure can be described as two three-arm stars which are bridged with a common fourth arm. Model super-H-shaped block copolymers of the PI3(PS-d8)PI3 type, where PI is protonated polyisoprene and PS-d8 is deuterated polystyrene, were synthesized by anionic polymerization using the chlorosilane approach. These nonlinear block copolymers were characterized by size exclusion chromatography (SEC), ultraviolet (UV) spectroscopy, low-angle laser light scattering (LALLS), and membrane (MO) and vapor pressure osmometry (VPO). The micellar behavior of these stars was investigated in n-decane, which is a selective solvent for the PI part. Small angle neutron scattering (SANS), LALLS, and viscometry were used in order to characterize the micelles. SANS measurements were performed at two different contrasts, where in each case one of the monomeric units was matched to the solvent. The coherent scattering cross sections of the single cores and coronas were determined by extrapolating low-concentration data to φ = 0. A theoretically calculated cross section of an unswollen hard sphere of PS-d8 was found to fit fairly well the experimental curves for the core. A calculated cross section of a hollow sphere with a constant density profile for the PI chains was found to describe the cross sections of the corona. Experimentally, it was found that the super-H structure increases the solubility and drastically reduces the aggregation number in comparison with linear PS/PI diblocks. A scaling approach is presented to take into account the specific influence of the SH structure on the micellar properties. It was found that the derived scaling laws of an intermediate regime between the starlike and the crewcut regime are in fair agreement with the experimental observations.

Test of Abnormally Large Coherent Scattering Cross Section Using Solar-Neutrino

We have carried out a high precision torsion balance experiment in searching for abnormally large coherent scattering cross sections between a sapphire crystal and solar-neutrino. According to the hypothesis and the experimental results presented by J. Weber, a diurnal effect, which was 60 times larger than the noise level, should be observed obviously, but no significant diurnal effects were found at the level of 8.1 × 10-8 dyn in our experiment.