Versatile Intense Triple-Axis Spectrometer

VERITAS |  HB-1A | HFIR

HB-1A Triple-Axis Spectrometer

Mission Statement

Diffraction studies of structural and magnetic phase transitions or parametric studies of low-lying magnetic excitations in novel materials.

Instrument Description

The VERITAS triple-axis spectrometer (HB-1A) at the High Flux Isotope Reactor operates at a fixed incident energy of Ei = 14.5 meV (wavelength λ = 2.37 Å) by employing a double-bounce pyrolytic graphite monochromator system. The first monochromator is flat, while the second monochromator is vertically focused. A highly-oriented pyrolytic graphite filter is placed after each monochromator to reduce λ/2 contamination (~0.01%). This configuration gives VERITAS an intense, clean monochromatic beam nearly free of higher-order contamination neutrons. The double-bounce monochromator system, combined with an analyzer for energy discrimination, ensures that the instrument has a low background and an excellent signal-to-noise ratio. The instrument is well-suited for probing weak scattering signals from single crystals, powders and thin films using a wide variety of sample environments, including high-temperature furnaces (≤ 1500°C), ultra-low temperature cryostats (≥ 0.03K), vertical field cryomagnets (≤ 8T), pressure cells (≤ 2GPa), and electric field sticks (≤ 10kV).

Applications

VERITAS is a versatile triple-axis spectrometer serving the condensed matter and materials science communities. The instrument is optimized for the following elastic and inelastic experiments:

  • Elastic scattering studies of structural and magnetic phase transitions and phase diagram mapping as a function of temperature, magnetic field, pressure, and electric field
  • Inelastic scattering studies of low-lying magnetic excitations with tunable energy resolution using different analyzers
     

VERITAS is primarily used to investigate the structural and magnetic properties of topical systems, including the following:

  • Quantum materials
  • High-Tc superconducting materials
  • Frustrated magnets
  • Multifunctional materials
  • Topological materials

Specifications

Beam Spectrum Thermal
Monochromator PG(002) crystal array
Monochromator angle 2Θ M = 41.3° Ei = 14.5 meV
Analyzers PG(002), Be(002), or Si(111) crystal array
Sample angles

±160°
Scattering angle -5 to 130°
Analyzer angles -60° < 2ΘA < 120°
Collimations Premonochromator: 40′
Monochromator-sample: 10′, 20′, 40′
Sample-analyzer: 20′, 40′, 80′ 
Analyzer-detector: 20′, 80′
Filters Sapphire pre-monochromator
2 pyrolytic graphite filters each mounted after
M1 and M2, respectively (λ/2 ≈ 10-4 λ)
Flux at sample ~4.2 × 107 n/cm2/s
Momentum range 0.2 to 4.8 Å-1 (elastic configuration)