[en] A multi-detector chopper spectrometer enables measurements of the scattering function S(Q,E) to be made over a wide range of momentum and energy transfer (Q,E). The application of pulsed-source chopper spectrometers for inelastic measurements at thermal and epithermal energies (50 meV < E < 1000 meV) is well known. Recently at IPNS, we have extended the energy-transfer region down to about 0.5 meV with a resolution of the order of 150 μeV. It is made possible by utilizing the cold-neutron incident spectrum of the 100 K methane moderator in conjunction with a dual beryllium-body rotor system. Neutron incident energies can be changed efficiently over the 4 to 1000 meV region while maintaining an undisturbed sample environment. We describe the operation of the IPNS chopper spectrometers (HRMECS and LRMECS), the instrumental resolution and the background-suppression performance. The capability of measuring inelastic features from 0.5 to 100 meV with an energy resolution of ΔE/E₀ = 2.5% is demonstrated by experimental results of crystal-field excitation spectra of a high-Tc superconductor ErBa₂Cu₃O₇. Preliminary data of quasielastic scattering from a room-temperature molten salt AlCl₃-EMIC are presented

[en] The electronic behavior of the ⁵I₈ Russell Saunders ground multiplet of Ho³⁺ in Pb₂Sr₂HoCu₃O₈ has been investigated using inelastic neutron scattering. We observe ten peaks in the excitation spectra that are associated with crystal field transitions. The peaks are only slightly broader than expected from instrument resolution, indicating that there are no strong interactions between the local Ho f states and the CuO conduction states. Comparing the energies and intensities of the experimental peaks with those expected from modeling convinces us that there are at least three states populated at the temperature of our experiment (15 K), making the assignments of transitions very difficult in the absence of further data

[en] The crystal-field splitting of the Er³⁺ ground multiplet ⁴I_15/2 in ErPO₄ is investigated by inelastic neutron scattering. Four excitations from the Γ₇ ground state to the excited states and several transitions between the excited states have been identified. The observed transition energies and intensities are used to refine the parameters of the crystal-field potential. The calculated magnetic susceptibility χ(T) agrees well with experimental values from single-crystal measurements. A comparison of the neutron data with optical absorption and both nonresonance and resonance Raman scattering measurements has been made

[en] The IPNS single crystal diffractometer (SCD) has been operating since 1981 primarily as a general purpose instrument for small molecule crystallography and for surveying reciprocal space. The instrument has recently undergone a major upgrade involving replacement of most of the hardware and software. In particular, two new position-sensitive scintillator area detectors based on the Anger camera concept were designed, fabricated and installed on the SCD. Each of these detectors have active areas of 15x15 cm² with a spatial resolution of better than 2 mm. A new data acquisition system permits the use of larger data files with a larger wavelength bandwidth at higher time-of-flight resolution. Software developed with tools in the ISAW workbench provides graphical manipulation of three-dimensional arrays of data in histogram coordinates and in reciprocal space, and user-friendly wizards for routine data analysis. As described in this paper, the upgrade of the SCD provides significant improvements in resolution, speed of data collection, and ease of use