Fixed-Incident-Energy Triple-Axis Spectrometer

Click for larger view of HB-1A photo

HB-1A Triple-Axis Spectrometer.

HB-1A is a fixed incident energy (14.6 meV) triple-axis spectrometer, using a double pyrolitic graphite monochromator system. The first monochromator is vertically focused and the second can be either a vertically or a double focused unit. Two HOPG filters, one after each monochromator, are used to reduce λ/2 contamination. These filters, together with the double monochromator system, provide HB-1A with an exceptionally clean beam in terms of higher order contamination neutrons; Iλ/2 ≈ 10-4 x Iλ/2. HB-1A also has one of the most intense beams at this energy at the HFIR, as well as a very low γ and fast neutron background. Typical energy resolution is ~1 meV but by using the Be analyzer the energy resolution width can be reduced to ~0.5 meV.

HB-1A development and operation is a collaborative effort of ORNL and Ames Laboratory.

HB-1A Schematic

HB-1A schematic.

Applications

  • Excitation spectra to ~35 meV using neutron energy gain, and low-lying excitations, 1-9 meV, using neutron energy loss.
  • Elastic studies on crystallographic and magnetic structures and transitions in a q range of 0.2 to 4.9 Å-1.
  • Elastic studies and excitations in thin films and other small volume samples where high flux and very low higher-order contamination of the beam are critical.