Instrument Description

HB-3 is a colossal flux thermal neutron three-axis spectrometer designed for inelastic measurements on single crystals over a wide range of energy and momentum transfers. Although the energy and momentum range for measurements is quite large, the instrument is ideal for experiments at high energy transfers. This is because of a combination of its location directly at the end of the beam tube and the availability of a beryllium monochromator. Experiments performed on HB-3 include excitations at high energies, such as phonons in high-temperature cuprates and magnons in iron and nickel. A wide range of sample environments, including closed-cycle helium (Displex) refrigerators 4He cryostats (with a dilution refrigerator option), cryomagnets, and furnaces can be accommodated on the instrument.

HB-3 has a variable-focus PG002 monochromator optimized for a 1 inch tall beam at the sample position over a broad range of incident energies, thus optimizing the incident neutron flux at each energy.

Pyrolitic graphite provides the highest neutron intensity because it has a high neutron reflectivity. The high-quality beryllium monochromator allows measurements with good energy resolution. Silicon 111 crystals have the advantage that there is no second-order reflection, thus providing a higher order contamination-free beam. The availability of these three monochromator crystal choices makes this spectrometer extremely versatile for a wide range of studies of the properties of materials.

The in-pile collimation can be reduced from its intrinsic value of 48' to a user-selectable value of 30' at the push of a button via the shutter control panel. This spectrometer also provides an in-pile sapphire filter for the white beam before the monochromator. Söller collimators from the monochromator-sample, the sample-analyzer, and the analyzer-detector can be changed as required by the user. The beam diameter of the effective source that illuminates the monochromator is 4.625 inches.

Applications

The availability of three different monochromator crystals makes HB-3 an extremely versatile instrument for studies of excitations in materials with energies ranging from 2 to 100 meV. Typical applications include spin and lattice dynamics in high-temperature superconductors and related compounds; low-dimensional magnetic model systems; magnetic excitations and phonons in colossal magnetoresistive materials, multiferroics, and ruthenates; and spin waves in magnetically ordered materials. The high incident neutron flux makes HB-3 well suited to studying samples that have a small volume or weak scattering characteristics.

Specifications

Beam Spectrum:Thermal
Monochromators:Variable vertical focusing PG(002), Be(101), Si(111)
Analyzer:Fixed veritcally focused PG(002), Si(111), Be(101)
Monochromator angle:12 – 88°
Sample angle:+/- 180°
Scattering angle-90° – 120°
Analyzer angle:-40 – 90°
Collimations (FWHM):Premonochromator: 30', 48'
Monochromator-sample: 20', 40', 60', 80'
Sample-analyzer: 20', 40', 60', 80'
Analyzer-detector: 30', 70', 90', 120', 210', 240'