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Asterix

A special strength of Asterix is the ease with which a great variety of experimental requirements can be accommodated.

Contacts  

  • Instrument Scientist
  • Erik Watkins
  • (505) 667-4037
  • Email

Surfaces and Interfaces

Asterix is a reflectometer/diffractometer/grazing-incidence-SANS/SESAME-enabled-SANS spectrometer that is primarily used for experiments or neutron scattering techniques requiring polarized neutron beams. These experiments involve studies of magnetic materials and to a smaller (though growing) extent non-magnetic systems—the latter taking advantage of the Spin Echo Scattering Angle Measurement (SESAME) technique. Examples of programs using Asterix include: polarized neutron reflectometry of magnetic materials (in low and 11 T-strong fields), long-wavelength/large-d-spacing diffraction (d-spacing > 2 Å) and measurements of pair correlation lengths up to 2 µm in soft matter.

Asterix views an intense polychromatic neutron beam through a 36-cm 2 neutron guide. Efficient polarization of the neutron beam with a 2.5 cm by 6 cm cross-section, a 4 to 13 Å wavelength range with divergence of the neutron guide is achieved using a state-of-the-art polarization cavity. The location of the instrument in the quiescent environment of Experiment-Room-2, and robust neutron shielding greatly minimize instrumental background.

A special strength of Asterix is the ease with which a great variety of experimental requirements can be accommodated. Use of non-magnetic materials in the neutron shielding assure compatibility of the spectrometer with LANSCE’s 11-T superconducting magnet, and has enabled the implementation of neutron spin-echo techniques. The 2.5-m long detector arm is readily configurable for polarization or energy analysis of the scattered neutron beam.

Special sample environment capabilities exist, including, for example, the capability to simultaneously expose samples to infrared laser light, magnetic fields, and neutron beams in an “ILL orange” cryostat or 11-T super-conducting cryomagnet. A 3 He insert enables measurements of samples to temperatures as low as 260 mK for all experiments using the 11 T magnet. A 4K Displex cryostat is configured to perform measurements of a sample’s resistivity. The Displex cryostat can also accommodate our four-point bending jig. The jig is capable of applying pure bending stress to very thin (up to 250 ±m thick) samples. Strains of ±0.1% have been achieved with ceramic oxide substrates.

Specifications

Moderator
Lower-tier coupled liquid-hydrogen moderator
Beam cross-section
- Polarized
- Unpolarized
 
25 mm – 60 mm
60 mm by 60 mm
Beam polarization
Unpolarized and polarized beams are routinely used. Two polarization analyzers are available.
Primary flight path
Target to sample position: 18 m
Secondary flight path
Sample to detector position: 0.5 – 2.5 m
Wavelength frame
4 to 13 Å
Resolution
Time-of-flight (wavelength) resolution 0.2 to 0.6%
Geometrical resolution > 0.04cotθ (%)
Neutron detector
(reflectometry)
One-dimensional position sensitive detector (PSD) on a detector arm with range of motion from 6° - 40°. The PSD can be rotated 90° about the normal to the detector face.
Neutron detector
(Grazing incidence SANS)
Two-dimensional PSD on a detector arm with range of motion from 6° - 40°. The PSD is equipped with two 3He pencil detectors that can be translated in the horizontal and vertical directions.
Neutron detector
(Spin Echo Scattering Angle Measurement, SESAME)
In addition to the one and two-dimensional PSD’s, some SESAME experiments use an array of twelve 3He pencil detectors for extremely high count rate measurements.
Neutron detector
(diffraction)
Two-dimensional array of PSD tubes that can be placed anywhere inside the Asterix cave. Maximum scattering angle is 100°.
Sample environment options tailored for Asterix experiments
11T superconducting 260 mK-300 K cryomagnet.
xyz-cryomagnet (1.7 to 300 K)
electromagnet (1.9 T across a 1 cm gap without cryostat or 1 T with a cryostat)
“Orange” cryostat for reflectometry, SANS or diffraction (1.7 to 300 K)
4-300 K Displex cryostat equipped with electrical leads for transport measurements
4-point bending jig to apply pure bending stress to substrates measuring 1 cm by 1 cm by 250 µm. The bending jig is intended for use in the 4K Displex cryostat.
808 nm 30 W fiber optic laser, with optical enclosure for the “Orange” cryostat.
Other options available, contact the instrument scientist.