search form

search form
High-Resolution Chopper Spectrometer (Pharos) 
Date of Last update : 2014.09.16 Rivision Request
Photos
Location
Lujan Center, Group Office TA-53, Bldg. 622, Rm. 220, LANSCE, Los Alamos National Lab, Los Alamos, NM 87545 USA
Homepage
http://lansce.lanl.gov/lujan/instruments/PHAROS.shtml
Coordinating Country
United States
Hosting Organisations
Lujan Neutron Scattering Center at Los Alamos Neutron Science Center (LANSCE) of Los Alamos National Laboratory
Contact Person
Dr. Victor Fanelli (+1-505-667-8755, vfanelli@lanl.gov)
RI Category
Analytical Facilities
Keywords
condensed-matter, local structure, magnetism, nanomaterials
Description
Pharos is designed for studies of fundamental excitations in condensed-matter systems.
Application Area
Pharos is designed for studies of fundamental excitations in condensed-matter systems.

Pharos can accommodate the full range of inelastic scattering experiments on liquid, polycrystalline, and single-crystal samples. This includes phonon and spin-wave dispersions, phonon density-of-states, magnetic excitations, momentum distributions, spin-orbit and crystal-field levels, chemical spectroscopy, and measurements of S(Q, ω) in disordered systems. In addition, the low-angle detectors are available for use at distances between 4 and 10 meters with scattering angles down to 0.65°, thus making it suitable for high-resolution inelastic studies (< 1% resolution) at low Q.
Specifications

Pharos provides 2% to 4% incident energy resolution and uses a high-speed Fermi chopper to obtain monochromatic incident energies in the range from 10 meV to 2 eV. The sample is positioned 20 meters from a chilled-water moderator. The spectrometer consists of an evacuated, shielded flight path with 10 m2 of meter-long position-sensitive detectors located at a distance of 4 meters from the sample and covering scattering angles between -10° and 145°.



Phonon dispersion of Pb at room temperature as measured by Pharos. The intensity of phonon branches are shown as a function of energy transfer and scattering angle. The data can be used to obtain the forces between Pb

atoms and verify first-principles electronic-band structure calculations used in equation-of-state efforts.



Specifications:

- Incident energy resolution: ??Ei/Ei = 2% - 4%

- Moderator-chopper distance: 18 m

- Chopper-sample distance: 2 m

- Moderator: Chilled water at 283 K

- Fermi chopper frequency: 60 - 600 Hz

- Fermi chopper diameter: 10 cm

- Fermi chopper slit spacing: 1 mm or more

- Sample size: up to 5 cm x 7.5 cm

- Detectors: 10 m2 of meter-long position-sensitive detectors at 4"m from the sample and scattering angles between -10° and 145°; 1 m2 of detectors in forward scattering position can be moved up to 10 m from the sample.