FSANS –Time of Flight Small Angle Neutron Scattering instrument
Instrument scientists: János Füzi, Adél Len
The FSANS diffractometer covers a Q-range from 0.0003 to 0.03 Å-1 and complementary to the Yellow Submarine SANS instrument allows to probe structures at length scales from 100 Å to 5000 Å. It has a wide range of applications from studies of defects and precipitates in materials, surfactant and colloid solutions, ferromagnetics, magnetic correlations, alloy segregation, polymers, proteins, biological membranes. The instrument is installed on the bottom section of the curved neutron guide No.3, made of m = 2 supermirrors.
Figure 1. Post sample flight tube and detector positioning mechanism of the FSANS diffractometer.
The beam time structure is provided by 4 choppers: a counter-rotating pair of pulse definition choppers, one wavelength limiting and one frame overlap chopper. The available wavelength range is 2 - 16 Å. The width Δλ of the wavelength uncertainty can be set by choosing the pulse definition chopper window to 0.3 A° with 8° opening (better resolution mode) or 0.75 A° with 20° opening (higher intensity mode) respectively. The collimation distance is 3.7 m, the sample to detector distance 4.3 m.
Samples from several millimetres to several tens of centimetres in diameter can be placed at the sample position, the beam size can be varied from 4 (pinhole collimation mode) to 40 mm (focusing mode) in diameter.
Detector and Data acquisition
The scattered neutrons are detected by a 256 x 256 pixels (0.7 mm x 0.7 mm pixel size) two dimensional position sensitive detector filled with 3He gas. Data acquisition is performed in event recording mode. Figure 2 displays an example of a small angle scattering measurement. Data were collected on both FSANS and Yellow Submarine instruments.
Figure 2. Small angle scattering curve measured on pottery control samples on the FSANS (left side) and Yellow Submarine (right side) instruments.
Figure 3. Layout of the FSANS diffractometer with pinhole collimation
Figure 4. Layout of the FSANS diffractometer with focusing collimation