Instrument description
The instrument MEREDIT starts to operate for researchers at the beginning of the year 2009. The essential part of the diffractometer - a multi-detector bank - comes from the decommissioned research reactor in Studtsvik in Sweden.
MEREDIT layout
The diffractometer consists of two large HUBER goniometer circles. The smaller one provides enough space for placing the different sample environments (see below). The detector bank is mounted in a moulded neutron shielding made from boron carbide powder in epoxy resin. The bank contains 35 3He point counters with corresponding 10' Soller collimators. They are all individually adjustable and set at angular intervals of 4.00° 2θ. The detector bank moves on air pads, which provides together with the stepping motor smooth positioning of this heavy loaded bank. Diffraction patterns can be collected in the angular range from 2 to 148 degrees in 2θ with step down to 0.02° and step delay controlled by strict time or neutron flow read by monitor.
Three individual wavelengths of the secondary beam can be selected for measurement using two different automatically exchangeable monochromators. The details about the monochromators and corresponding secondary neutron beam parameters can be found here.
All movable parts are driven by stepping motors and controlled by PC. The data from 35 counters are collected using two 24-channel Tedia cards. All communication and data collection is made with help of the special software ReMeSys (Regulation and Measurement System). This software is under continuous development to provide the best interface for our diffraction instruments and can easily adopt new extensions and experimental needs. The experiment flow is controlled by scripts written in Pascal like language what provide high flexibility needed for automation of complex experiments.
There are several sample environments to enhance the measurement ability of the instrument: vacuum furnace able to cover the measurement from the room temperature up to ~1000°C; light furnace covering the same temperature range (RT up to 1000°C) but in addition is possible to heat up the sample on different atmospheres including open air, close cycle cryostat operating from room temperature down to ~10K; sample changer - carousel - for up to six samples measured at room temperature. A special deformation rig permits in-situ measurements under uni-axial stress/pressure or fatigue cycles. For textured samples, it is also possibility to mount up the Euler goniometer.
For the powder samples we use the vanadium containers with different diameters - 6, 10 and 13 mm. These containers can be used ONLY for measurement in the carousel, vacuum furnace and the close cycle cryostat.
Applications
Investigation of atomic and magnetic structure with all advantages and also disadvantages of the neutron powder diffraction. Using the different sample environments is possible to make temperature dependency of structural/magnetic parameters. With deformation rig in-situ strain and/or stress control diffraction experiment able to see multiple reflections of studied material.
Practical examples already studied on the MEREDIT instrument:
- phase transformation in the cast iron during the tensile load
- conduction path way in the oxygen conductors for fuel cell membranes
- doping level of the hydrogen storage material
- in-situ chemistry during charging in the lithium batteries
- magnetic structure of magneto-caloric compounds
- magnetic structure of antiferromagnetic semiconductors for spintronic devices
- base and corrosion materials in archaeological artifacts
- twinning model in the magnesium alloys during tension and compression
- and many others
International collaboration
The diffractometer has been incorporated in the international NMI3 (Integrated Infrastructure Initiative for Neutron Scattering and Muon Spectroscopy) project. Within this project collaboration with international institutions and researchers will be carried out and can be financially supported. For more information consult access page and the links therein.