ECHIDNA - High Resolution Powder Diffractometer

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Engineering drawing of the ECHIDNA High-Resolution Powder Diffractometer (August 2003)
Engineering drawing of the ECHIDNA High-Resolution Powder Diffractometer (August 2003)
The Ge-113 monochromator has been acquired from the Brookhaven National Laboratory.
The Ge-113 monochromator has been acquired from the Brookhaven National Laboratory.

ECHIDNA is the name of the new neutron High Resolution Powder Diffractometer at Australia's new research reactor OPAL, ANSTO.

The instrument serves to determine the crystalline structures of materials using neutron radiation analogical to X-ray techniques.

It will operate with thermal neutrons. One of the main features is the array of 128 collimators and position sensitive detectors for rapid data acquisition. ECHIDNA will allow structure determinations, texture measurements and reciprocal space mapping of single crystals in most different sample environments serving the physics, chemistry, materials, minerals and earth-science communities. ECHIDNA is part of the Bragg Institute's park of neutron scattering instruments.

The Australian instrument, mother of all monsters, is named after the Australian monotreme echidna. Spiny peaks allude to the high resolution of the instrument.

Contents

[edit] Components

  • Neutron guide
    The instrument is located on the TG1 thermal neutron guide of the OPAL reactor. The distance from the reactor is 58 m. The position is the second on the guide after the WOMBAT instrument. The size of the guide is 300 mm height X 50 mm width and it is plated with supermirror coatings.
  • Primary collimator
    There are Söller collimators prior to the monochromator in order to reduce the divergence of the beam and to increase the angular resolution of the instrument. Since this is an intensity compromise, two items of 5' and 10', respectively, can be interchanged or fully removed by an automated mechanism. The collimators cover the full size of the beam delivered by the neutron guide.
  • Monochromator
    The monochromator is made by slabs of [113] oriented Germanium crystals which are inclined towards each other in order to focus down the Bragg reflected beam. The device has been acquired from the Brookhaven National Laboratory in the USA after the shutdown of their neutron facility.
  • Secondary collimator
    Optionally a secondary collimator with 10' angular acceptance and 200 mm X 20 mm can be placed in the monochromatic beam between the monochromator and the sample, which again influences the resolution function of the instrument.
  • Slit system
    Two automated sets of horizontal and vertical pairs of absorbing plates allow to cut down the size of the monochromatic beam prior to the secondary collimator and sample size. They remove unwanted netrons and reduce the background near the detector. In addition, they allow to select the sample position to be studied.
  • Beam monitor
    A 235U fission monitor measures the amount of neutrons incident to the sample. The efficiency is 10-4 and most neutrons traverse the device undisturbed. The monitor counts are important to correct for beam flux variations due to changes in the reactor or at the upstream instrument.
  • Sample stage
  • Detector collimators
  • Detector tubes

[edit] Applications

[edit] Literature

[edit] External links

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