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  • 1
    Electronic Resource
    Electronic Resource
    Measurements of radius of gyration and persistence length in bulk atactic polystyrene by low-angle neutron scattering (1974)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 7 (1974), S. 190-190 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The radius of gyration, rg, of atactic polystyrene molecules in the bulk polymer has been measured by low-angle neutron scattering from dilute solid solutions of poly-proto-styrene in poly-deutero-styrene with concentrations of 5 % and 0.5 % tagged solute molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889874009204
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  • 2
    Electronic Resource
    Electronic Resource
    Instrumental resolution effects in small-angle neutron scattering (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 438-451 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Experimentally measured scattering data differ from theoretical curves because of departures from point geometry in a real instrument. In a small-angle neutron scattering (SANS) instrument, there are essentially three contributions to the smearing of an ideal curve: (1) the finite divergence of the beam, (2) the finite resolution of the detector, and (3) the poly chromatic nature of the beam. Where the scattering is azimuthally symmetric about the incident beam, indirect Fourier transform (IFT) methods may be used not only to smear an ideal scattering curve, but also to desmear an observed pattern. For experiments where the assumption of azimuthal symmetry cannot be made, alternative procedures based on Monte Carlo (MC) techniques have been developed which simulate the smearing of a given theoretical scattering function. This procedure permits the evaluation of smearing effects in anisotropic systems. Both IFT and MC procedures are illustrated with a range of applications from data taken on the 30 m SANS facility at Oak Ridge National Laboratory. It is shown that for experiments with scattering dimensions 〈 200 Å smearing effects are small (〈 5%) and that dimensions up to ̃1200 Å may be accurately resolved after proper evaluation of resolution effects. The procedures described may also be extended to include small-angle X-ray scattering, and an example of one such application is given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888004273
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  • 3
    Electronic Resource
    Electronic Resource
    Absolute calibration of small-angle neutron scattering data (1987)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 20 (1987), S. 28-40 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Absolute calibration forms a valuable diagnostic tool in small-angle neutron scattering (SANS) experiments, and allows the parameters of a given model to be restricted to the set which reproduces the observed intensity. Discrepancies between the observed and calculated intensities may arise from potential artifacts or even new physical processes and absolute calibration methods are useful in delineating these circumstances. General methods which are available for absolute scaling are discussed along with estimates of the degree of internal consistency which may be achieved between the various standards. In order to minimize the time devoted to calibration in a given experimental program, emphasis is placed on developing a set of precalibrated strongly scattering standards which may be run in the chosen experimental geometry. Comparison of such a set developed at the National Center for Small-Angle Scattering Research (Oak Ridge) with independent determinations by SANS users indicates consistency to within ± 5%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889887087181
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  • 4
    Electronic Resource
    Electronic Resource
    Estimation of incoherent backgrounds in SANS studies of polymers (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 469-475 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Small- and intermediate-angle neutron scattering studies have been undertaken on mixtures of deuterated and protonated poly(ethylene terephthalate) (PET) molecules with a wide range of concentration. The samples were converted to random copolymers by transesterifying in the melt, thus removing the coherent component of the intensity associated with single-chain scattering. The transesterified samples were used to determine the level of incoherent scattering associated with each isotopic mixture which was compared with estimates from established background-correction techniques based on extra-polating from the scattering of fully protonated or deuterated blanks. Scaling via the measured sample transmission works well for predominantly protonated mixtures but fails when the fraction of deuterated polymer exceeds φD 0̃.6. Scaling via the component of the sample transmission attributable to the incoherent scattering from H nuclei works well over the whole concentration range. This method involves calculations of the sample transmission via the bound-atom cross section and this is a good approximation at the wavelength employed (λ 4̃.75 Å), where the hydrogen incoherent cross section is close to the bound-atom cross section (σH 8̃0 × 10−28 m2). However, σH is a strong function of wavelength and the method cannot be used where the measured and calculated transmissions diverge. A recently developed theory describing the scattering from random copolymers was used to analyze the residual coherent cross section of the copolymers and led to a statistical segment length b = 14.3 ± 1 Å, in good agreement with existing values for PET.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889890006215
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  • 5
    Electronic Resource
    Electronic Resource
    The effects of instrumental distortion in X-ray diffraction studies of liquids. II. Collimation distortion (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 44-49 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The effects of collimation distortion on the measured diffraction curves from `amorphous' solids and liquids are discussed. It is shown how the parameters governing the range of angular divergence may be obtained and how the `permissible' range of scatter angles may be established. Model calculations and experiments were performed to show some of the distortion effects which can occur in the measured interference function if the permissible range of scatter angles is exceeded. It is shown that distortion effects are potentially most severe where line sources are employed, and it is therefore recommended that in future, collimation limits are calculated and stated. If it proves necessary to use collimation limits which distort the data in order to achieve satisfactory intensity, then these limits should be chosen so that analytical correction procedures to correct the data are possible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889878012650
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  • 6
    Electronic Resource
    Electronic Resource
    Calculation of double scattering of X-rays in two scattering geometries for a compressible fluid (argon) (1974)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 7 (1974), S. 366-369 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Numerical estimates of double scattering of X-rays have been made in cylindrical and parallel-plate geometries for fluid argon in two states. For the cylindrical geometry the ratio of double scattering to single scattering is 0̃.01 and independent of scatter angle to a first approximation, and thus does not seriously effect estimates of the radial distribution function. For the parallel-plate geometry the ratio is to a first approximation linear with angle and increases to 0̃.15 at high angles; it thus seriously effects estimates of the radial distribution function and direct correlation function. The ratio can reach very high levels at low scatter angles if primary scattering is low.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889874009812
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  • 7
    Electronic Resource
    Electronic Resource
    Intercalibration of small-angle X-ray and neutron scattering data (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 629-638 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Absolute calibration forms a valuable diagnostic tool in small-angle scattering experiments and allows the parameters of a given model to be restricted to the set which reproduces the observed intensity. General methods which are available for absolute scaling of small-angle X-ray scattering (SAXS) data are reviewed along with estimates of the degree of internal consistency which may be achieved between the various standards. In order to minimize the time devoted to calibration in a given experimental program, emphasis is placed on developing a set of precalibrated strongly scattering standards for the SAXS facilities of the National Center for Small-Angle Scattering Research (Oak Ridge). Similar standards have been developed previously for calibration of small-angle neutron scattering (SANS) data. Particular attention is given to standards which can be used for either SAXS or SANS experiments where each sample has been independently calibrated for both types of radiation. These calibrations have been tested via the theoretical relationships between the two cross sections. It has been found that specimens best suited for such intercalibration purposes are a glassy carbon specimen where the scattering arises from voids in a carbon matrix and a perdeuterated polyethylene where the scattering arises from periodic arrangement of the crystalline lamellae. In only these two cases could the identical specimen be used for both the neutron and X-ray scattering experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888004820
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  • 8
    Electronic Resource
    Electronic Resource
    Small-angle neutron scattering studies of chain conformation in semicrystalline hydrogenated polybutadiene (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 701-706 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Mixtures of model crystallizable copolymers, hydrogenated polybutadiene (HPB) and deuterated polybutadiene (DPB), were investigated by SANS in the intermediate q range (0.02 ≤ q ≤ 0.18 Å−1). Linear and three-arm-star polymers were crystallized by quenching and slow cooling at rates differing by 3000-fold. Care was taken in subtracting the incoherent background scattering. The coherent cross section shows a q−2 dependence which results in a constant Kratky plateau. Absolute SANS intensity is slightly greater than predicted for amorphous chains and is very insensitive to crystallization conditions in these polymers, changing by less than 10%. These observations are interpreted in terms of the gambler's-ruin model for chain configurations in semicrystalline polymers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888006818
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  • 9
    Electronic Resource
    Electronic Resource
    Reduction of parasitic scattering in small-angle X-ray scattering by a three-pinhole collimating system (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 241-245 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A series of experiments have been undertaken on the Oak Ridge National Laboratory (ORNL) 10 m small-angle X-ray scattering (SAXS) camera to provide quantitative data on the level of background (parasitic) scattering generated by different types of bevelled collimating slits. The addition of a third (guard) slit, positioned close to the sample, resulted in a reduction of over an order of magnitude in the parasitic background generated by the best two-slit combination of collimating slits. This made it possible to reduce the size of the beamstop, permitting useful data to be collected down to a value of the scattering vector Q = 4πλ−1sinθ ∼ 3 × 10−3 Å−1, where λ is the wavelength, and 2θ is the angle of scatter. This permits the resolution of distances d ̃2π/Q up to 2000 Å.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889890001984
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  • 10
    Electronic Resource
    Electronic Resource
    The effects of instrumental distortion in X-ray diffraction studies of liquids. I. A study of the relative effectiveness of several monochromatizing techniques (1975)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 8-11 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Some experimental and theoretical comparisons have been made of the effectiveness of four techniques which have been commonly used for monochromatizing X-radiation for use in diffraction studies of liquids: monochromator crystals, curved or flat; β-filter and pulse-height analyzer; balanced dual filters. The β-filter/pulse-height analyzer system alone results in unacceptable error, at both low and high s(s = 4πλ−1 sin&thgr;). Dual filters can be made quite effective, actually approaching the resolution possible with monochromator crystals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889875009429
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