Table 1.
Specifications and anticipated performance of the Fermi Chopper Spectrometer. Additional details are given in the text
| Specifications | ||
| Guide cross section (height × width): | 150 × 60 mm | |
| Maximum beam size (height × width): | 100 × 25 mm | |
| Monochromators (double): | Pyrolytic graphite PG(002) | |
| 1st Monochromator (height × width/type): | 160 × 100 mm/flat | |
| 2nd Monochromator (height × width/type): | 184 × 100 mm/vertically focussing | |
| Monochromator mosaic (vertical/horizontal): | 25750′ | |
| Intermonochromator collimation: | 60′ | |
| Beam filters (thickness/type/temperature): | 152 mm/Be/77 K for λ > 0.4 nm | |
| 38 mm/PG/296 K for select λ <0.4 nm | ||
| Fermi chopper details (2 slit packages) | Package 1 | Package 2 |
| Blade curvature radius: | 389.0 mm | 581.4 mm |
| Rotor radius: | 26.9 mm | 25.6 mm |
| Slot width: | 0.635 mm | 0.635 mm |
| Beam window (height × width): | 100 × 25 mm | 100 × 25 mm |
| Optimum chopper speed: | 80.93/λ(nm)Hz | 54.15/λ(nm) Hz |
| Sample — detector distance: | 2.286 m | |
| Scattering angle range: | 5° < ϕ < 140° | |
| Post-Sample radial collimation (oscillating) | ||
| Blade separation: | 3° | |
| Inner/Outer radius: | 203/305 mm | |
| Detectors (cylindrical, 3He-filled) | ||
| Fill pressure: | 0.4 MPa | |
| Diameter: | 25 mm | |
| Angular separation: | 1.273° | |
| Quantity/Active height: | 12/229 mm for 5° <2θ <20° | |
| 88/457 mm for 20° < 2θ < 140° | ||
| Incident wavelength range: | 0.23 < λ0 0.61 nm (÷2 for PG(004)) | |
| Incident energy range: | 15.5 >E0 > 2.2 meV (×4 for PG(004)) | |
| Elastic momentum transfer range: | 1< Q < 50 nm−1 (×2 for PG(004)) | |
| Anticipated performance | ||
| Fluence rate on sample: | ∼1 × 108 n/m2/s at λ =0.24 nm | |
| ∼1.2 × 108 n/m2/s at λ = 0.40 nm | ||
| Elastic energy resolution: | 40 μeV at λ = 0.60 nm | |
| 150 μeV at λ = 0.40 nm | ||
| 600μeV at λ=0.24 nm | ||
| Q Resolution: | ΔQ/Q < 3% | |