National user facilities such as the NIST Center for Neutron Research (NCNR) require a significant base of software to treat the data produced by their specialized measurement instruments. There is no universally accepted and used data treatment package for the reduction, visualization, and analysis of inelastic neutron scattering data. However, we believe that the software development approach adopted at the NCNR has some key characteristics that have resulted in a successful software package called DAVE (the Data Analysis and Visualization Environment). It is developed using a high level scientific programming language, and it has been widely adopted in the United States and abroad. In this paper we describe the development approach, elements of the DAVE software suite, its usage and impact, and future directions and opportunities for development.

We describe the design and current performance of the high-flux backscattering spectrometer located at the NIST Center for Neutron Research. The design incorporates several state-of-the-art neutron optical devices to achieve the highest flux on sample possible while maintaining an energy resolution of less than 1 µeV. Foremost among these is a novel phase-space transformation chopper that significantly reduces the mismatch between the beam divergences of the primary and secondary parts of the instrument. This resolves a long-standing problem of backscattering spectrometers, and produces a relative gain in neutron flux of 4.2. A high-speed Doppler-driven monochromator system has been built that is capable of achieving energy transfers of up to ±50 µeV, thereby extending the dynamic range of this type of spectrometer by more than a factor of two over that of other reactor-based backscattering instruments.

Incoherent neutron scattering measurements were performed on polycarbonate (PC), poly-(methyl methacrylate) (PMMA), and poly(vinyl chloride) (PVC) films of variable thickness, ranging from bulklike down to 75 Å, or length scales comparable to the polymer's radius of gyration. The temperature dependencies of the incoherent elastic scattering are analyzed in terms of a Debye-Waller factor to estimate the hydrogen-weighted mean-square atomic displacement 〈u 2 〉. We find a general reduction of 〈u 2 〉 as the polymer films become increasingly thin, especially above the calorimetric glass transition temperature, Tg. However, below Tg this reduction depends strongly upon the relative amplitude of the displacement. Specifically, if 〈u 2 〉 in the bulk glass is especially large, as seen in PC, the extensive sub-Tg motions are strongly suppressed by thin film confinement. On the contrary, glassy PVC displays comparatively small-amplitude displacements in the glass and virtually no reduction of 〈u 2 〉 upon confinement. These results are discussed in terms of a caging of the atomic motions as the degree of thin film confinement increases.