Disordered Materials Diffractometer
Reactor Hall, Level C, Hot Beam H8
Si(11L=1,2,3), Cu(220) and Cu(331), all 20 cm high and 23 cm wide,
Flux at sample
~5.0·107 n cm-2 s-1
for λ=0.7 Å (167 meV) / Cu220
~5.0·107 n cm-2 s-1
for λ=0.5 Å (327 meV) / Cu220
~0.75·107 n cm-2 s-1
for λ=0.35 Å (668 meV) / Cu331
Continuously variable (see IN1 specifications).
2x2-slit horizontal + vertical diaphragm at 30 cm upstream of sample,
20 mm diameter by 50 mm height
9 x 64 cells under 15 bar of 3He
100 mm height by 160 mm width
The D4 instrument is a two-axis neutron diffractometer equipped with nine 1-D position-sensitive microstrip detectors pressurized with 3He gas to 15 bar for efficient detection of short-wavelength neutrons from the ILL's hot source.
The monochromator take-off angle is 2θM ≈ 20-40°, variable. The available monochromators are all horizontally and vertically focusing: Cu (220) for λ = 0.7 Å, Cu (220) for λ = 0.5 Å, Cu (331) for λ = 0.35 Å.
All three monochromator faces are 20 cm high and 23 cm wide. The Si(11L=1,2,3) face is not advantageous for these three standard D4 wavelengths.
Filters for λ/2 harmonic contamination are available for λ = 0.7 and 0.5 Å, Ir and Rh, respectively. A high-transmission monitor located between monochromator and beam-defining slits is used for normalisation to incident beam intensity.
The sample is mounted in an evacuated cylindrical bell jar (Ø = 46 cm, 55 cm height) with a wide-angle thin aluminum exit window. The samples are usually contained in cylindrical vanadium cans. Vertical and horizontal slits allow defining a maximum illuminated cross-section of 5 cm (Vert) and 2 cm (Horiz).
The instrument is equipped with nine 3He-gas 1D position-sensitive detectors, with a cell spacing of 2.5 mm. The distance between sample and detection surface is 1146 mm, giving an angular spacing of 0.125º per cell. Each detector of 64 cells covers therefore 8º in 2θ. Since there is a 7º gap between two detectors, at least 2 angular positions of the 9-detector ensemble are required to produce a complete diffractogram, and normally scans of 5 or 6 angular positions are used in order to equilibrate counting statistics. The final available 2θ-range of the diffractogram is 1.5º to 140º.
Each detector has its own evacuated collimating tube, containing B4C or 10B4C (detector 1) collimation rings placed at positions so as to suppress background intensity and to block spurious Bragg peaks coming from the bell jar's aluminum exit window. Each microstrip detector, located in a 3He chamber at about 15 bar, consists of an electrically-conducting glass substrate supporting photo-lithographically deposited anodes and cathodes, providing very high counting-rate stability.
Standard non-ambient sample environments include a cryofurnace (2 to 550 K) and a vanadium furnace (50 to 1150 C). The sample bell jar is big enough to accommodate specialized or user-provided equipment, such as high-pressure cells (including Paris-Edinburgh) or non-standard furnaces (including aerodynamic levitation with laser heating).
Counting statistics of 0.1% per 0.125º can be obtained in about 3 hours for a sample of average dimensions and scattering cross-section. More information on the characteristics of the D4c instrument can be found in the following standard reference:
H.E. Fischer, et al, Appl. Phys. A 74 (2002) S160--S162.