HK3 - Thermal neutron analytical methods

Three instruments HC3-a HC3-b and HC3-c operate at the thermal neutron beam formed by short neutron guide tube. The neutron guide ensures an efficient transport of thermal neutrons from a Ć 100 mm horizontal channel of the reactor to small target areas of the HC3-a, HC3-b and HC3-c spectrometers. The neutron guide is built of a mirror type tube of rectangular cross-section, cylindrically bent in the vertical direction. It consists of 15 mirror sections made of glass plates of float type. The surface of these plates is coated with Ni reflecting layer with thickness of 2000 Ă. The internal cross-section of each mirror section is 4×150 mm². The overall length of the guide is 5.63 m, the curvature radius being 825 m. In order to suppress a background due to a direct beam of gamma rays and fast neutrons, the guide is tightly surrounded by a combined shielding consisting of lead and polyethylene pellets. Unlike thermal neutrons, gamma rays and fast neutrons are not subject to reflections from the Ni coating and penetrate the guide walls. In the shielding around they are scattered and absorbed and only collimated thermal neutrons pass through. In addition, a biological shielding, formed by boron-doped polyethylene and lead bricks, is built along the whole guide. The shape of the incoming neutron beam at the entrance of the guide matches the cross-section of the guide. This has been achieved using a 90 cm long collimator made of lead with a rectangular aperture. Immediately behind the guide exit, the neutron beam is tailored by an additional collimator made of ⁶Li₂CO₃ to reduce the beam cross-section to 4×60 mm². The flux of thermal neutrons at the guide exit averaged over the beam cross-section is (1.5±0.2)·10⁷n cm^-2 s^-1. The cadmium ratio is equal approximately to 10⁵. The above mentioned fluxes refer to the reactor power of 8 MW. Beyond the guide exit, the vertical divergence of neutron trajectories is characterized by angular deviations below 0.5°.

HK4 - Multipurpose Double Axis Diffractometer SPN-100

The two-axis diffractometer SPN-100 is equipped with bent Si and Ge perfect single crystal monochromators easily changeable according to the experimental requirements. The diffractometer is usually used for macro/micro strain scanning of polycrystalline materials. An easy change of the instrument parameters permits one to use it also for another type of experiments. The diffractometer uses advantages coming from focusing both in real and momentum space and yields good resolution and luminosity especially for samples of small dimensions. The resolution properties of the device arereached in a limited Q-range for which the focusing conditions are optimized. The corresponding optimization can be done easily by using a remote control of the curvature of the monochromator. Depending on the sample-detector distance and the required resolution the PSD detector can cover 7° (15°) of the scattering angle 2Q_S. In the case of the strain scanning of the sample, the gauge volume is determined by two fixed Cd slits (2-5)x(3-30) mm² in the incident and diffracted beams and the measurements are performed in the vicinity of 2Q_S=90°. For scanning the sample a x-y-z stage can be used. The instrument is controlled by PC. Recently, the diffractometer has been equipped with a sandwich type monochromator consisting of two bent crystal slabs of different cuts providing two different neutron wavelengths simultaneously (Si(111) + Si(220), Si(220) + Ge(311)). This monochromator is mainly used for strain measurements when providing more sample reflections in the range of the investigated scattering angles.

MEREDIT - Neutron Powder Diffractometer

The neutron powder diffractometer MEREDIT (MEdium REsolution neutron powder DIffracTometer) was made operational for scientists at the end of the year 2008. It is placed on the horizontal channel number 6 in the reactor hall of LWR15 (light water reactor) in Řež near Prague.

This instrument is mainly dedicated to the study of the crystalline and/or magnetic structure of the powder or polycrystalline samples. Due to the several sample environments including vacuum furnace, close cycle cryostat, Euler goniometer, deformation rig, etc. is this instrument an universal tool for researchers whose want to use advantages of neutron powder diffraction.

Old version of the web pages is still available here.

HK8 - SANS and Neutron Optics Diffractometers

Neutron beam at the channel HK8 hosts two experimental facilities: High-resoiution SANS Diffractometer (MAUD) and Neutron Optics Diffractmeter (NOD). The two instruments use monochromatic beams selected by bent Si 111 and Si 220 monochromators situated in common shielding block. Such a construction is possible thanks to the very low absorption of silicon for thermal neutrons so that the first monochromator leaves the wavlength band for the second one almost intact. The common primary beam is shaped by a newly installed (in 2009) collimator with dimensions optimized for the beam size and divergence employed by the SANS instrument. It contains 10 cm thick sapphire filter and a sequence of B₄C and Pb inserts in order to minimize gamma and neutron background and to suppress contamination of the beam by high-order Bragg reflections. The monochromators shielding is composed from inner Pb container and outer 40 cm thick wall made of concrete filled with B₄C powder. The secondary collimators are equipped with horizontally and vertically adjustable slits, which permit fine tuning of required beam size delivered to the sample area.

High-Resolution Stress/Strain Diffractometer (TKSN-400)

TKSN 400 is a high resolution two-axis diffractometer optimized for investigation of internal stresses in polycrystalline materials. Due to its equipment, the instrument is dedicated especially for thermo-mechanical testing of materials, i.e. to study the deformation and transformation mechanisms of modern types of newly developed materials. Neutron diffraction performed in situ upon external loads, brings a wide range of valuable structural and sub-structural parameters of the studied material which is easy to correlate with parameters of external loads.

Neutron activation analysis