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High Resolution Neutron Powder Diffractometer (PSD)

The PSD powder instrument is designed to optimize the neutron flux and resolution available at a medium-sized source. The features that are primarily responsible for its resolution and intensity characteristics are the double focusing perfect crystal Si monochromator and a detector bank of five, vertically stacked linear position sensitive detectors (LPSD´s). The monochromator was developed at MURR by Mihai Popovici. It uses the (511) reflection of Si so that the takeoff angle is nearly 90° and has a mosaic spread of about 2 arcmins. With this arrangement, no Soller-slit collimators before or after the sample are required. The beam is focused in both the vertical and horizontal directions by arranging the 9 Fankuchen cut Si (511) blades along a vertically curved frame and by applying a bending strain in the horizontal direction. The oscillating radial collimator limits the background neutrons coming from outside the scattering volume. The LPSD´s cover an angular range of 20° so that a complete diffraction pattern of 100° is obtained by stepping the detector bank through five positions. The instrument wavelength is λ=1.485Å, which is very close to the peak of the Maxwell-Boltzmann distribution of a thermal neutron beam. The instrument has a long and productive history and has been used for exploring structural and/or magnetic phase transitions, high temperature superconductors, and colossal magnetoresistive (CMR) materials, just to name a few.

Photo of the High resolution powder diffractometer (PSD)
  • Monochromator: Double focusing bent perfect Fankuchen cut Si (511) crystal (λ=1.485 Å)
  • Detectors: 5 linear position sensitive 3He tubes, 24´´ sensitive length, covering 20° per detector position
  • Collimation: Oscillating radial collimator
  • Resolution: 1.5 x 10-3 (Δd/d)
  • 2θ range: typically 5° to 105°
  • Sample environment: variable temperature from 5K to 800K