EPSILON-MDS and SKAT
Instruments Responsible:
EPSILON - Dr. V. Sikolenko
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
Tel.+7 (49621) 6-40-45, 6-47-98
SKAT - Dr. D. Nikolaev
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+7 (496) 216-59-72
External team members:
This email address is being protected from spambots. You need JavaScript enabled to view it. (KIT Karlsruhe Institute of Technology, Germany)
This email address is being protected from spambots. You need JavaScript enabled to view it. (Institute of Earth Sciences, University of Kiel, Germany)
Niko Froitzheim (University of Bonn, Germany)
Main research fields:
Measuring tension, strain and texture in geological, metal and ceramic samples.
The strain/stress diffractometer EPSILON-MDS
The EPSILON diffractometer, designed as strain/stress diffractometer allows to investigate bulk samples and to resolve strain in space and time, separately for each phase. A 4-axes goniometer allows a rotation about one axis and translations in 3 mutual perpendicular directions. It is therefore well-suited to measure strain profiles or the six independent components of the strain tensor. High precision sample positioning is achieved by means of step motors. A deformation device is available for in-situ deformation experiments, to investigate applied strain behaviour. The equipment is fully remote controlled and very well suitable for uniaxial load up to 100 kN. Nine collimator-detector units are arranged at angles of -21°, 0°, 21°, 69°, 90°, 111°, 159°, 180°, and 201° around the incident beam,each unitcovers a 2θ-range of 82° ≤ 2θ ≤ 98°. This allows the simultaneous measurement of nine sample directions.
Sample environments:
- uniaxial pressure device (150 MPa) for in-situ stress experiments,
- acoustic emission detection system,
- laser extensometer for macro-strain measurements: resolution: 0.5 µm,
- Furnace till 130 °C, can work together with pressure device.
Instrument characteristics
| Total flight path (moderator - detector) | ~107 m |
| λmax | 7.1 Å |
| λmax (by using the beam chopper) | 14.4 Å |
| dmax | 5.1 Å |
| dmax (by using the beam chopper) | 10.2 Å |
| Neutron guide | beam cross section: 50 mm (w) × 90 mm (h) bending radius: 13400 m coating: natural Ni (m=1) option: chopper covering every 2nd neutron pulse |
| Detectors | 81× 3He single tubes, diameter: 10 mm active length: 120 mm |
| Collimators: length divergence of the foils 2θ-range size of entrance window size of exit window |
nine radial collimators, foils GdO2-coated 500 mm 20’ of arc 82° ≤ 2θ ≤ 98° 50 × 50 mm2 200 × 200 mm2 |
| Spectral resolution Δd/d | 4·10-3 at d ≥ 2 Å |
| Goniometer Φ-rotation x-, y-translation z-translation accuracy |
4-axes goniometer 0° to 360° 120 mm 40 mm 0.0025° and 0.0025 mm, respectively |
| Uniaxial pressure device | F= 100 kN (P= 150 MPa) |
| Sample dimensions | Ø = 30 mm, l = 60 mm |
| Maximal sample volume | 42 cm3 |
| Thermal conditions | stabilized: ±1K |
| Sample adjustment | by laser beams |
| Experiment control | SONIX-software PC-based measuring system W |
The strain/stress diffractometer EPSILON-MDS, equipped with 9 radial collimators at 2θ = 90°, the four-axes-goniometer and the uniaxial pressure device (right).
Schematic sketch of the experimental geometry at strain/stress diffractometer EPSILON-MDS
The high-resolution texture diffractometer SKAT
Summary
The SKAT is a multi-detector diffractometer consisting of three independent detector systems. Each detector system is characterized by unique scattering geometry of the detectors. Selecting the optimum scattering angle 2θ allows adaptation of the accessible d-range and resolution Δd/d to sample requirements. If desired, the wavelength range may be expanded by an additional beam chopper, which covers every second neutron pulse.
Instrument description
The SKAT diffractometer comprises three ring-shaped carriers, each bearing up to 19 detector-collimator units located at 2θ = 65° / 90° and 135°, respectively. The three detector systems are developed for an alternative use, detector-collimator units are exchangeable between systems. Selection of a unique scattering angle for the detectors results in identical positions of the diffraction peaks, hence, all λ- and θ- dependent corrections can be avoided.
The 2θ = 65° detector system allows texture experiments with good resolution up to a maximum lattice spacing of dmax = 6.5 Å. A single sample resolution around an axis Z at an angle of 57.5° with respect to the incident neutron beam is sufficient to cover the whole pole figure.
The 2θ = 90° detector system allows high resolution texture experiments up to a maximum lattice spacing of dmax = 5.0 Å. A single sample resolution around an axis Z at an angle of 45.0° with respect to the incident neutron beam is sufficient to cover the whole pole figure. The goniometer angle of 45° offers the optimum conditions for the installation of uniaxial sample environments for in situ experiments.
The 2θ = 135° detector system allows very high resolution texture experiments up to a maximum lattice spacing of dmax = 3.9 Å. Two goniometer positions (Z at 22.5° and 67.5°) are required to cover the whole pole figure.
Layout of the SKAT detector systems for alternative use.
The sample is rotated around the axis Z, for the detector system 2θ = 135° two sample positions P1 and P2
are required. Sample movements around the X and Y axes are also possible.
Photograph of the SKAT with the detector system at 2θ = 90° and the goniometerfor sample rotation (status December 2006)
Predicted resolution of the SKAT detector systems, derived from experimental dataof the former neutron guide for sample rotation (status December 2006)
Instrument characteristics
| Primary beam path | ~ 104 m | ||
| Optional scattering angles 2θ | 65° / 90° / 135° | ||
| λmax | 7.0 Å / 14.6 Å* | ||
| 2θ-related parameters | 2θ = 65° | 2θ = 90° | 2θ = 135° |
| dmax | |||
| Best resolution Δd/d | 6.2·10-3 | 5.0·10-3 | 3.1·10-3 |
| Secondary beam path | 1.10 m | 1.00 m | 0.95 m |
| Neutron guide | Cross section: 50 mm (w) × 90 mm (h) Radius: 13400 m Coating: natural Ni (m = 1) Option: chopper covering every 2nd neutron pulse |
||
| Detectors | Set of 19 3He single tube detectors P = 4.5 bar Ø = 60 mm |
||
| Secondary collimation | Two sets of Gd-coated soller collimators Angular dispersion: 18' / 45' Cross section: 55 × 55 mm2 |
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| Sample positioning | 3 axes goniometer | ||
| Data acquisition system | SONIX software PC running MS Windows | ||
* applying the primary beam chopper
Strain/stress and texture measurements on geological samples
Most geological materials are composed of crystals with generally non-random crystallographic orientation. All non-random crystallographic orientations in a polycrystal are termed 'preferred orientations' or 'textures'. Most physical properties of polycrystals are anisotropic, i.e., depending on the direction in which they are measured. Both these fundamental observations are the starting point for numerous applications of texture and anisotropy analyses in Earth sciences: 1. Deformational processes in the Earth's crust and mantle lead to lattice preferred orientation of the rock-forming minerals. The deformation history of rocks may be derived from the mineral textures. 2. From the mineral textures and known physical anisotropy of minerals, the physical state of rocks in the deep Earth may be derived. 3. Determination of residual and applied intracrystalline strain/stress in combination with acoustic emission registration in order to unreavel microscopical mechanisms of stress formation. This is important to explain the tectonic stress behaviour in the upper Earth's crust and for the understanding of the processes taking place during earthquake events.
Spectra: TOF spectrum of three-phase geological sample consisting of calcite, quartz, dolomite. Due to high resolution the textures of all the phases could be determined successfully.
Publications
Walther, K., Scheffzuek, C., Frischbutter, A. (2000). Neutron time-of-flight diffractometer epsilon for strain measurements: layout and first results. Physica B, Condensed Matter 276-278, 130-131.
Ullemeyer, K., Spalthoff, P., Heinitz, J., Isakov, N.N., Nikitin, A.N., Weber, K. (1998). The SKAT texture diffractometer at the pulsed reactor IBR-2 at Dubna: experimental layout and first measurements.- Nuclear Instruments and Methods in Physics Research A412, 80-88.