MTEST

Material Test Diffractometer

Instrument responsible: László Temleitner

The M(aterial) TEST neutron diffractometer is a general-purpose neutron powder diffractometer. It covers the range of medium-resolution powder, liquid and amorphous total diffraction (Bragg and diffuse scattering) measurements. The available sample environments allow to perform powder studies between 77K — 1273K. Spinning, scanning or orienting (by Eulerian-craddle) the samples is possible at room temperature.

The MTEST diffractometer is installed on axial thermal channel No. 6 of the reactor. The maximum flux can be obtained at a neutron wavelength of 0.144 nm. A sapphire single crystal, positioned deep inside the beam shutter, filters out the epithermal neutrons. The neutron flux at the sample table is 2*106 neutron/(cm2*sec) at a wavelength of 0.133 nm. The standard size of the beam is 10 mm (width) x 40 mm (height), which can be adjusted by slits for the required size.

The instrument is equiped with a monochromator changer which uses 3 crystals: Ge(111), Cu(111) and Cu (220), allowing to tailor the beam for the required Q-range and resolution even during data collection on a sample (see Table 1).

Table 1. Some typical setup

Setup Monochromator Wavelength [Å] Q-range [Å-1] Best resolution Intensity
"Disordered crystal" Cu(111) 1.45 0.45 - 8.1 0.6° 100%
"Medium resolution crystal" Cu(220) 1.35 0.5 - 8.5 0.6° 40%
"Liquid/amorphous" Cu(111) 1.11 0.65 - 10.6 1.2° 85%
"Medium-Q liquid/amorphous" Cu(220) 0.89 1.0 - 13.1 1.0° 10%
"Low-Q liquid/amorphous" Ge(111) 2.27 0.25 - 5.1 1.2° 6.5%

A low efficiency fission chamber monitor and an Ordela position sensitive detector (with two sample/detector positions) serve for data collection. The ultimate angular upper limit of the detector in near and far positions is 141° and 151°, respectively. However, the pattern from 7° to 138° can be recorded by 5 positions in the "near" and from 6° to 139° by 12 positions in the "far" positions. The background level in “near” position equals to the scattered intensity from that of a 6 mm diameter, 0.05 mm thick, 40 mm long vanadium sample holder.

To mount samples for room temperature measurements, standard O-ring sealed vanadium cans (6 and 8 mm in diameter) are available.

Additional sample enviromnents:

  • low background vanadium vacuum furnace (RT-1000°C)
  • aluminium-shielded cryostat (77K-RT)
  • X,Y scanning table for residual stress measurements

Our group collaborates with the users, by taking part in the experiemntal work, through data evaluation, simulation to publication of the results.

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Figure 1. MTEST overview: sample changer with the "near" position of the detector in the center and vacuum furnace on the left. The width of the dark foot at the left bottom corner corresponds to about 12 cm.

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Figure 2. Side view of the room temperature sample changer setup at MTEST.