Polarized Triple-Axis Spectrometer

PTAX |  HB-1 | HFIR

HB-1Polarized Triple-Axis Spectrometer

Mission Statement

HB-1 is a versatile spectrometer to study static and dynamic properties of spin and lattice using polarized and unpolarized neutrons.

Instrument Description

Of the four triple-axis spectrometers installed at HFIR, HB-1 is specifically designed for polarized beam measurements, but it is also a highly efficient general-purpose unpolarized neutron spectrometer. The choice of two monochromator plugs gives this instrument great versatility. The polarizing plug accommodates the fixed vertical focusing Heusler alloy monochromator with a vertical guide field. The unpolarized plug accommodates a pyrolitic graphite (PG) monochromator with variable vertical focusing. The instrument offers a choice of Heusler alloy (for polarized experiments) and PG (unpolarized or half-polarized) analyzers. The polarized setup is designed to be compact enough to accommodate all available sample environment equipment, including a 4He/3He dilution refrigerator, standard 4He flow cryostats, a cryofurnace, and a variety of closed-cycle refrigerators. Using the Wollaston Prisms setup, ultra-high energy and Q resolution measurements have become possible (https://fankangli.ornl.gov/). The newly implemented spherical neutron polarimetry (SNP) enables the measurement of full polarization change in the scattering process, providing a unique way to study complex magnetic structures (jiangc@ornl.gov).

Applications

HB-1 is suited for parametric studies of spin and lattice excitations in specific areas of energy and momentum space in materials, such as multiferroic materials, thermoelectric materials, high-temperature superconductors, geometrically frustrated magnets, and quantum magnets, using high flux polarized and unpolarized neutrons. It can accommodate a wide variety of sample environments including high temperature furnaces (< 1770 K), ultra-low temperature cryostats (> 0.05K), vertical field cryomagnets (< 8T), pressure cells (< 2GPa), and electric field sticks (< 10kV). The half polarization technique is used to map out spin density distributions in magnetic compounds and observe chirality in frustrated magnets. The longitudinal polarization analysis is used to determine detailed spin direction and also separate magnetic and nuclear components in magnetic materials. The materials best suited for study on HB-1 facilitate power and data transmission in computers, cell phones, and power lines; impact the capacity of computer memory (hard disk); improve the efficiency of electric devices and power plants; and are vital to the eventual development of a quantum computer.

Specifications

Beam Spectrum Thermal
Monochromators Unpolarized PG(002) (variable vertically focused)
Polarized Heusler(111) (fixed vertically focused)
Analzyers
Unpolarized PG(002), Be(101), Si(111) (fixed vertically focused)
Polarized Heusler (111) (flat)
Monochromator angle 2ΘM = 14 – 45°
Sample angle +/- 180°
Scattering angle –90 – 120°
Analyzer angle –40 – 140°
Collimations (FWHM) Premonochromator: 15', 30', 48'
Monochromator-sample: 20', 40', 60', 80'
Sample-analyzer: 20', 40', 60', 80'
Analyzer-detector: 20', 70', 90', 120', 210', 240'