Fixed-Incident-Energy Triple-Axis Spectrometer (HB-1A)
| Beam Spectrum: | Thermal |
| Monochromator: | PG(002) double crystal |
| Monochromator angle: | 2Θ M = 41.3° Ei = 14.64 meV |
| Analyzers: | PG(002) Be(101) Be(002) Si(111) Ge(111) |
| Sample angles: | 0° < Ψ < 360° |
| Scattering angle: | -15° < Φ < 140° |
| Analyzer angles: | -60° < 2ΘA < 120° |
| Collimations (FWHM): | C1: open (48′ effective) C2: open (40′ effective) (30′, 20′, 10′) C3: 40′, 30′, 20′,10′ (sample-analyzer) C4: 34′, 68′, 136′ (analyzer-detector) |
| Beam Size: | 40 × 150 mm max |
| Filters: | Sapphire pre-Monochromator-1 HOPG (λ / 2 ≈ 10-4λ) located between M-1 and M-2 and after M-2 |
| Flux at sample: | ~2 × 107 n/cm2/s (est.) |
HB-1A Schematic
HB1A is a fixed incident energy (14.6 meV) triple-axis spectrometer, using a double pyrolitic graphite monochromator system. The first monochromator is vertically focused and the second can be either a vertically or a double focused unit. Two HOPG filters, one after each monochromator, are used to reduce λ/2 contamination. These filters, together with the double monochromator system, provide HB1A with an exceptionally clean beam in terms of higher order contamination neutrons; Iλ/2 ≈ 10-4 x Iλ/2. HB1A also has one of the most intense beams at this energy at the HFIR, as well as a very low γ and fast neutron background. Typical energy resolution is ~1 meV but by using the Be analyzer the energy resolution width can be reduced to ~0.5 meV.
HB1A development and operation is a collaborative effort of the ORNL and Ames Laboratory neutron scattering groups.
Recent experiments on HB1A include measurement of phonon dispersion curves in martensitic, shape-memory and magnetostrictive alloys, crystallographic and magnetic structure determinations in giant magnetocaloric, magnetoresistive and intermetallic alloys, magnetic structures and spin-density waves in thin films, magnetism in low-dimensional systems and spin waves and magnetic structures in magnetoelectric materials.
Applications
- Excitation spectra to ~35 meV using neutron energy gain, and low-lying excitations, 1-9 meV, using neutron energy loss.
- Elastic studies on crystallographic and magnetic structures and transitions in a q range of 0.2 to 4.9 Å-1.
- Elastic studies and excitations in thin films and other small volume samples where high flux and very low higher-order contamination of the beam are critical.
HB-1A Triple-Axis Spectrometer. Click image for a larger view.
