16 Oct 2008



The General Materials Diffractometer is a new generation neutron diffractometer. GEM can be used to perform high intensity, high resolution experiments to study the structure of disordered materials and crystalline powders.

​​​​​​​​​Gem instrument at target station 1


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.

Instrument links: 

Contact information for the Gem instrument​

Location and contact information for the Gem beamline

Telephone01235 445198