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Instrument Hb1a

For more information, contactInstrument Scientist: Jerel Zarestky,, 865.574.4951 The Fixed-Incident-Energy (14.6 meV) Triple-Axis Spectrometer uses a double pyrolitic graphite monochromator system. The first monochromator is vertically focused, and the second can be either a vertically or doubly focused unit. Two highly oriented pyrolytic graphic filters (HOPG), one after each monochromator, are used to reduce /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: I /2 10-4 x I . This spectometer also has one of the most intense beams at this energy at the HFIR, as well as a very low and fast neutron background.

Typical energy resolution is ~1 meV, but, using the beryllium analyzer, the energy resolution width can be reduced to ~0.5 meV.

HB-1A development and operation is a collaborative effort of the Oak Ridge National Laboratory and Ames Laboratory neutron scattering groups.

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 -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 Recent experiments on this instrument include measurement of phonon dispersion curves in martensitic, shape-memory, and magnetostrictive alloys; crystallographic and magnetic structure determinations in giant magnetocaloric, magnetoresistive, and intermetallic alloys; magnetic structures and spin-density waves in thin films; magnetism in low- dimensional systems; and spin waves and magnetic structures in magnetoelectric materials.

06-G01640D/gim Beam spectrum Thermal Monochro- mator PG(002) double crystal Monochro- mator takeoff angle 2 M = 41.3 E, = 14.7 meV Analyzers PG(002), Be(101), Be(002), Si(111), Ge(111) Sample angle 0 to 360 Scattering angle -5 to 135 Analyzer angles -60 to 120 Collimations (FWHM) Premonochro- mator: 48' Monochroma- tor-sample: 10', 20', 30', 40' Sample-ana- lyzer: 10', 20', 30', 40' Analyzer-detec- tor: 70', 140' Beam size 40 150 mm max Filters Sapphire pre- monochro- mator 2 HOPG; after M1 and M2 Flux at sample ~ 2 107 n/ cm2/s (est.) Momentum range 0.2 to 4.9 -1 (elastic con- figuration) Energy transfer ~-35 meV to ~+11 meV at q = 3 -1 Specifications March 2010 Status: Operational

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