Description

HEiDi was build for structural investigations of single crystals using neutron diffraction. Neutron radiation is guided via the beam tube from the reactor core through the primary collimator. The collimator removes disturbing scattered radiation and reduces the horizontal divergence of the primary beam to a suitable value.
After passing the primary channel in the biological shielding the remaining radiation reaches the monochromator. The monochromator selects a suitable wavelength λ from the radiation spectrum and guides it under a diffraction angle of 2θ_M through one of the three secondary beam channels in the shielding to the sample.
The sample is mounted on the diffractometer itself. Because of its Eulerian geometry this device can orient the sample virtually in any direction corresponding to the incomming beam. By this the secondary beam which is diffracted from the sample under the angle of 2θ can be directed to the detector.
The Detector detects the incoming radiation, using a ³He single counter or a 2D multidetector.
The basic control system of the instrument consists of a Siemens Profibus controller which is usually used for industrial CNC devices. This Siemens controller itself communicates with a Linux PC which also manages data collection.

Special Features

The following special features are available to increase the efficiency of the instrument:

• Temperature dependent measurements
  For certain investigations, e.g. of structural phase transitions, HEiDi can be equipped with special sample environments, a furnace and a closed cycle cryostat. Therefore one can perform diffraction experiments in a wide temperature range between 4 Kelvin and 1300 Kelvin.
• Pure elastic diffraction
  Using an Analyser of pyrolytic graphite-(002) one can suppress detection of neutrons scattered in the neighbourhood of the sample and pure elastic scattering can be measured.
• Time optimized data collection
  A typical single crystal diffractometer spends up to 50% of the complete time of measurement for the positioning of its axes. By optimizing the coordination of the axes and data collection this dead time can be reduced to a minimum.
• Optimized background correction
  By using a small twodimensional detector, one can perform a much more accurate background determination than by using a single counter. This increases quantitative data analysis significantly.