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A neutron spin filter based on transmission through nuclear-spin-polarized 3He gas has been applied to polarization analysis of small angle neutron scattering (SANS). Such spin filters, which are based on the large spin dependence of the absorption of neutrons by 3He, make SANS polarization analysis possible because of their large angular acceptance. In the present experiment, a 3He-based analyzer was employed to separate nuclear scattering into its coherent and spin-incoherent components. Polarized 3He analyzers were prepared by two different optical pumping methods and installed on the NG3 SANS instrument at the NIST Center for Neutron Research (NCNR). Measurements were taken on cellophane tape and silica gel, for which the scattering is almost completely incoherent and coherent, respectively, and on a combined sample. For the combined sample, separation of the coherent part from the incoherent part was successfully demonstrated using polarization analysis.

Two high-resolution, general-purpose, small-angle neutron scattering instruments have been constructed at the National Institute of Standards and Technology's Center for Neutron Research. The instruments are 30 m long and utilize mechanical velocity selectors, pinhole collimation and high-data-rate two-dimensional position-sensitive neutron detectors. The incident wavelength, wavelength resolution and effective length of the instruments are independently variable, under computer control, and provide considerable flexibility in optimizing beam intensity and resolution. The measurement range of the instruments extends from 0.0015 to 0.6 A−1 in scattering wavevector, corresponding to structure in materials from 10 A to nearly 4000 A. The design and characteristics of the instruments, and their modes of operation, are described, and data are presented which demonstrate their performance.

Quasielastic gamma‐ray scattering of 46.5‐keV Mossbauer photons by polydimethylsiloxane has been studied at room temperature as a function of dilution in benzene. The high energy resolution of this novel technique allowed the separation of the scattering signal into a narrow component associated with stiff motions along the polymer chain backbone and a quasielastic component associated with softer side group motions. The narrow component disappears upon dilution in benzene while the intensity of the quasielastic component grows proportionately. This result is interpreted as a softening of the backbone normal modes upon dilution.

If one expands the expression of the intensity scattered by polymers or copolymers in the large q range, one observes that, for Gaussian chains, this intensity follows a law of the type i(q) = Aq-2 + Bq-4. The coefficient A characterizes the length of the statistical element, and the coefficient B is easily measured using the Zimm representation. For a linear chain B gives the number-average degree of polymerization. In the case of branched polymers without loops, it depends mainly on the number of statistical elements between two cross-links or one cross-link and an end. If the polymer is sufficiently long, it gives the number-average degree of polymerization of these branches. A general formula is given and applied to classical examples: star, alternating, a comblike copolymer. The effect of polydispersity and the case of block copolymers with blocks of different chemical nature are discussed. These results are also extended to stretched polymers. This method could give new information in the interpretation of neutron scattering data.

A recently developed M\"ossbauer instrument has been used to study the liquid dynamics of pentadecane at various temperatures and scattering angles. Widths of the quasielastic signal extracted from the data ranged between 16 GHz (at 12 \ifmmode^\circ\else\textdegree\fi{}C) and 48 GHz (at 74 \ifmmode^\circ\else\textdegree\fi{}C) at a scattering vector of 1.15 A${\mathrm{\r{}}}^{\mathrm{\ensuremath{-}}1}$. Similar measurements at five different scattering angles (at 12 \ifmmode^\circ\else\textdegree\fi{}C) were also taken to investigate the Q dependence between 0.82 and 1.56 A${\mathrm{\r{}}}^{\mathrm{\ensuremath{-}}1}$. The results obtained are in good agreement with classical theory for coherent scattering from liquids.

There is previous evidence that random copolymers of bisphenol A carbonate (BPAC) and dimethylsiloxane (DMS) form microdomain morphology. Small-angle neutron scattering (SANS) is used to investigate this system, which shows a broad-peak spectrum. The origin of this peak is due to interference scattering between the BPAC-rich microdomain and the DMS-rich interdomain regions. SANS measurements taken from such a random copolymer (50%/50% mixture) under uniaxial external stretch show that the glassy microdomains do not follow the external drawing whereas the rubbery interdomain regions do. Two data analysis methods are used: one based on nonlinear least-squares fits of the raw data to a model consisting of two confocal ellipsoids representing the deformed microdomain morphology and the other on a two-di- mensional Fourier transform of SANS data to obtain an anisotropic pair correlation function.