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BRISP
Time of Flight Neutron Spectrometer for Small Angle Inelastic Scattering
Characteristics
| Reactor hall, thermal beam IH3 |
|---|
| Monochromator | |||
|---|---|---|---|
| Double focusing– horizontal variable focusing.Incident beamarea at the monochromator: 6 x 6 cm2.Monochromator surface:20.8 x 8.6 cm220 crystals in a 4 x 5 matrix:crystal size4 x 2 cm2,mosaic spread0.4° (PG) and 0.25° (Cu) | |||
| crystalPG(002)Cu(111)PG(004) | d-spacing (Å)3.355(nominal)2.0871.677(nominal) | λ0(Å)1.977(expt.)1.28 (expt.)0.989(expt.) | E0(meV)20.9 (expt.)49.9 (expt.)83.6 (expt.) |
| Collimation |
|---|
| Soller Collimatorα1 = 0.4°700 mm length - 5 mm slit spacing16 Gd2O3 coated Kapton sheets, 75 µm thickHoneycomb Collimatorα2 = 0.4°2000 mm length, Gd2O3-coated aluminumhoneycomb arrangement of converging tubes of hexagonal section3 different collimators for convergence at 2**, 4(recommended), 6 m from the sample positioncollimators are maintained under vacuum and selected by means of a 4-sector revolverone sector is used for coarse collimation using 2 Cd diaphragms (in: 81x81 mm2, out: 67x67 mm2) |
| Choppers | |
|---|---|
| Background chopperFermi chopper | 5000 rpm max15000 rpm max |
| Sample | |
|---|---|
| Beam area at the sample depending on the monochromator and honeycomb collimator adjustement | |
| Sample chamber | diameter 500 mm, height 550 mmSilicon windows for vacuum separation. |
| Vacuum level in the sample chamber | 10-4mbarOrange MAXI cryostat:T=1.5-300 Ksample access diameter:100mm |
| Ancillary equipment | Furnace:T=300-1500KSample access diameter:40mm |
| Detectors | |
|---|---|
| PSD Reuter-Stockes3He multi-tube assembly1003He filled (15 bar) tubes, φ=1/2" 1m length | |
| Available detection area | 2.1 m2 |
| Detector arrangement | 128 central tubes:diameter 12.7 mm, length 1118 mmSide wings of 16 tubeseach: diameter 12.7 mm, length 600mm |
| Pixel size | Height:0.43 mmWidth:12.7 mm0.86 mm |
| Distances, useful ranges and resolution (approximate values) | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Monochromator – Fermi chopper | 5540 mm | ||||||||||
| Fermi chopper – Sample | 1000 mm | ||||||||||
| Sample – Detector Dsd (variable) | 2000-6000 mm | ||||||||||
| E0(meV) | Dsd | Energy TransferE(meV) | Angular andQelranges | Resolution | ||
|---|---|---|---|---|---|---|
| DE/E0 | DQ(Å-1) | |||||
| 20.9 meV | 2 m4 m6 m | ± 18± 14± 12 | 1° - 15°1° - 15°1° - 9° | 0.05-0.8 Å-10.05-0.8 Å-10.05-0.5 Å-1 | 3%2.9%2.4% | 0.02 |
| 49.9 meV | 2 m4 m6 m | ± 50± 45± 35 | 1° - 15°1° - 15°1° - 9° | 0.09-1.3 Å-10.09-1.3 Å-10.09-0.8 Å-1 | 3.8%3%2.7% | 0.03 |
| 83.6 meV | 2 m4 m6 m | ± 80± 70± 60 | 1° - 15°1° -15°1° - 9° | 0.1-1.7 Å-10.1-1.7 Å-10.1-1.0 Å-1 | 4.5%3.2%3.1% | 0.04 |
** Please ask the instrument responsible for this configuration
Instrument description
Keywords in the design of the BRISP spectrometer were
- Thermal neutron energies: allowing for investigations in systems characterized by sound velocities up to 3000 m/s (three different incident energies between 20 and 80 meV are presently available).
- Easy small-angle access: enabling low-Q spectroscopy with thermal neutrons. Elastic wavevector transfer values Qel as low as 0.03 Å -1 at 20 meV incident energy can be reached. The position of the two-dimensional detector can be adjusted to cover different small-angle ranges between 1° and 15°.
- Time-of-Flight technique: for an efficient data collection allowing also for accurate neutron measurements as a function of external parameters such as temperature, pressure and magnetic field.
- Careful optimization of monochromator-collimators-Fermi chopper: leading to 0.5 meV energy resolution and 0.02 Å-1 Q resolution in a typical configuration (20 meV incident energy and 4 m sample-detector distance), along with acceptable counting rates (flux at the sample 104 n s-1 cm-2). For this purpose, innovatory solutions were specially developed for some of the BRISP components.
Main components
- A Soller collimator defining the beam impinging on the monochromator, with a collimation angle of 0.4°
- Two focusing multi-crystal monochromators, PG and Cu(111), that allow for the selection of three incident energies in the range from 20 to 80 meV. Fixed/variable curvatures are adopted in/outside the Brisp vertical scattering plane.
- A disk chopper used for background reduction and selection of the desired monochromator reflection through proper phasing with the Fermi chopper.
- Three honeycomb converging collimators [1] to define the incident beam on the sample with a collimation angle of 0.4°, and to optimize convergence at three detector positions (2, 4, 6 m from the sample). A coarse resolution option is also available, without honeycomb collimator.
- A Fermi chopper producing short neutron pulses which enable the time-of-flight analysis.
- A high-vacuum sample chamber possibly equipped with 1.5-300 K MAXI Orange cryostat (100 mm) and 300-1900 K furnace
- A ~2 m2-area position sensitive gas detector (3He) whose distance from the sample can be varied between 2 and 6 m in order to access the required Q-range. A huge vacuum tank hosts the detector. An elastobore – polyethylene shielding surrounds the vacuum tank to reduce the environmental background.
- The long vacuum line ensures an under-vacuum neutron flight path from the background chopper to the detector.