Principle Measurements

• Pair distribution function (PDF) / total scattering measurements of disordered (poly)crystalline, nanocrystalline and amorphous materials.
• Powder diffraction measurements for Rietveld refinements of atomic and magnetic structure.
• Diffraction measurements of textured samples
  

Key Facts

• The GEM detector array was completed in December 2003.
• The completed GEM detector array has 7270 elements (not including monitors) in 86 modules.
• The GEM shutter was opened for the first time on 12th October 1999.
• The size of a typical datafile for one run on GEM is nearly 37 megabytes.
• The GEM detectors cover a scattering angle range from 1.1° to 169.3°.
• GEM's incident flight path is L1=17.0 metres.
• GEM's scattered flight path ranges from 1.0 metres to 2.9 metres.
• Over 100 kilometres of electrical cable were installed for the GEM detectors.
• When complete, the GEM scintillator detector system will contain 660,000 individual optic fibres, whose total length will be about 350 kilometres.
• The GEM vacuum vessel is made of 25mm grade 304 stainless steel, and is designed to attain pressures as low as 1x10-6 mbar.
• The windows in front of the detectors are 0.7mm aero grade aluminium - when the vacuum vessel is under vacuum, the windows deform by about 45mm at the centre.
• The GEM vacuum vessel has a volume of 1.3517m³ (i.e. 1351.7 litres).
• The GEM beam-stop weighs about 80 tonnes, with a canister of boron carbide at the centre to absorb neutrons.
• GEM has about 200 tonnes of bulk steel shielding, and about 43 tonnes of wax in shielding tanks.