[ Identification | Description | Input parameters | Links ]
ILL_IN4 InstrumentIN4C is a high-flux time-of-flight spectrometer used for the study of excitations in condensed matter. It works in the thermal neutron energy range (10-100 meV). Primary spectrometer The main components of the beam conditioning part are the two background choppers, the double curvature mono-chromator with four faces and the Fermi chopper. The background choppers are rapidly pulsating beam shutters which act as a low-pass filter. Thus they eliminate from the beam most of the fast neutrons and gamma rays that would give background noise in the spectra. The modular shielding encloses the background choppers in separate compartments in order to cut off these undesired neutrons as early as possible. A suitable energy is selected from the thermal neutron spectrum with the crystal monochromator. The monochromator, an assembly of 55 crystal pieces, concentrates the divergent incident beam onto a small area at the sample position. The full use of the available solid angle gives a high incident flux. The vertical curvature is fixed, and the horizontal variable curvature of the monochromator is essential in controlling the time and space focussing conditions for optimal performance (see H. Mutka, Nucl. Instr. and Meth. A 338 (1994) 144). The Fermi chopper rotates at speeds of up to 40000 rpm. It transmits short neutron pulses (10 ... 50 µs) to the sample. The time-of-flight of neutrons between the chopper and the sample (1 ... 5 ms) can be measured by using precise electronic circuitry. A sapphire (Al2O3) filter can be inserted in the beam to remove the fast neutrons background. Monochromators: PG 002 DM=3.355 AA (Highly Oriented Pyrolythic Graphite) PG 004 DM=1.677 AA (used for lambda=1.1) PG 006 DM=1.118 AA Cu 220 DM=1.278 AA Cu 111 DM=2.095 AA Take-off: 39-65 deg flux at sample: 5e5 n/s/cm2 (at 1.1 Angs) Secondary spectrometer The sample environment is designed to accommodate standard cryostats and furnaces. A radial collimator around the sample position is used to cut the scattering from the sample environment. The secondary flight-path is in vacuum to avoid parasitic scattering of the transmitted neutrons. The detector bank covers scattering angles of up to 120°. In addition to the 3He detector tubes (length 300 mm, width 30 mm, elliptical section, pressure 6 bar) a 3He filled multidetector (eight sectors with 12 radial cells each; outer diameter Phi 60 cm) will allow us to observe forward scattering. The time-of-flight spectra measured at various angles are further treated in order to obtain the scattering function S(Q,w) using e.g. LAMP. In this model, the sample is a cylindrical liquid/powder/glass scatterer surrounded by a container and an Al cryostat.
| Name | Unit | Description | Default |
| lambda | Angs | wavelength | 2.2 |
| dlambda | Angs | wavelength HALF spread at source | 0.1 |
| DM | Angs | monochromator d-spacing | 3.355 |
| ETAM | arcmin | monochromator mosaic FWHM | 35 |
| RMH | m | Monochromator horizontal curvature. Use -1 for auto. | -1 |
| ratio | 1 | Disk Chopper ratio (nu=nu_FC/ratio) | 4 |
| dE | meV | Inelastic energy for time focusing | 0 |
| Sapphire_present | 1 | Flag, when 1 the Al2O3 filter is active | 1 |
| sample_coh | str | Sample coherent dynamic structure factor (.sqw) or NULL | "Dirac2D.sqw" |
| sample_inc | str | Sample incoherent dynamic structure factor (.sqw) or NULL | "NULL" |
| order | 1 | The number of multiple orders at the monochromator | 1 |
ILL_IN4.instr.
[ Identification | Description | Input parameters | Links ]
Generated on 2023-09-19 20:01:36