Laboratory of nuclear analytical methods

1) Room temperature (RT) transmission 57Fe (or 119Sn) Mössbauer spectroscopy

Structural, phase, and magnetic characterization of iron containing samples using transmission MS method:

  • Element selective (Fe, Sn) determination and quantification of phase composition of samples including amorphous and nanocrystalline ones
  • Determination of valence and spin states of iron atoms, differentiation of their structure positions, stoichiometry, examination of cation substitution
  • Determination of the magnetic state and local configurations of magnetic moments of the atoms studying mechanism and kinetics of reactions in solid phase, phase or polymorphous transformations

57Fe Mössbauer spectra are recorded with 512 channels and measured at room temperature employing a laboratory Mössbauer spectrometer, operating at a constant acceleration mode and equipped with a 57Co(Rh) source.

The acquired Mössbauer spectra are processed (i.e., noise filtering and fitting) using the MossWinn software program.

2) Low temperature transmission 57Fe Mössbauer spectroscopy (5–300 K)

The low temperature Mössbauer spectra are recorded employing Cryostation (Montana Instruments) closed-cycle cryogen free system to which a Mössbauer spectrometer is mounted. The acquired Mössbauer spectra are processed (i.e., noise filtering and fitting) using the MossWinn software program. The isomer shift values were referred to α-Fe foil sample at room temperature.

Structural, phase, and magnetic characterization of iron containing samples using transmission MS method:

  • Measurement of temperature dependences (with low temperature equipment)
  • Determination of magnetic properties including temperatures of magnetic transitions (with low temperature equipment)

3) 57Fe Mössbauer spectrometer in a backscattering geometry

Backscattering geometry allows registration of Mössbauer spectra from compact (not necessarily powdered) and relatively larger samples.

4) Austenitemeter

Backscattering method of Mössbauer spectroscopy for analysis of surfaces of larger compact samples. It is especially equipped for metallurgical industry. The method allows fast and precise determination of content of retained austenite in low carbon steels. The method is suitable for investigation of corrosion processes as well.

5) Time Differential 57Fe Mössbauer spectrometer (TDMS)

Mössbauer spectrometer for Time Differential Mossbauer experiments can be operated in both, transmission and emission configuration. The spectrometer is equipped by specially designed detector, which allows detection of 122 keV photons in a nearly 4π solid angle. It is operated in the coincidence regime. Time resolution of the 122 keV and 14 keV photons delay is adjustable in the range of 1-20 ns.

Time differential arrangement of Mössbauer spectroscopy employs time filtering of gamma radiation with respect to a delay after gamma photon emitted during formation of relevant level. Using this technique we can decrease line widths by a factor of 1.5. Thus we can much better distinguish spectral lines that are close to each other, which is beneficial in case of evaluation of complex spectra. The technique provides possibility to investigate chemical aftereffects, i.e. processes which take place after the transmutation of Co atom to Fe atom.

6)57Co Emission Mössbauer spectrometers

Emission configuration of Mössbauer spectroscopy is used for investigation of hyperfine field in the radioactive sample in contrast to transmission Mössbauer spectroscopy, where the radioactive material is employed only as a source of gamma photons. Emission Mössbauer technique has 10-100 times higher sensitivity than transmission Mössbauer spectroscopy and thus offers unique information about the specific position, where the source of radiation (57Co) is introduced. The emission technique is capable to follow migration of atoms in the material, e.g. during diffusion, chemical reactions etc.

The emission spectrometers are operated in the virtual instrumentation platform [Pechousek et al., Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment Vol. 637, Issue 1, 2011, 200–205]. They consist of compact transducer working in the velocity range from –15 to +15 mm/s with a line width of 0.3 mm/s and scintillation detector. Since the count rate is rather small in emission spectroscopy, a NaI:Tl crystal is rather used due to reach a sufficient energy resolution. The first emission spectrometer (left figure) is equipped with a special sample holder, where the radioactive (analyzed) sample is static and the absorber moves. This setup is suitable for powder samples where the shaking of radioactive powder sample could cause enormous line broadening. The second spectrometer (right figure) is dedicated to compact emission samples because the radiation source moves while the absorber is static.

  

7) Mössbauer microscope

Recently, a development of Mössbauer microscope has been started. The method will be capable to get Mössbauer spectrum from a small area of the sample. The 14 keV photons from the Mössbauer source are focused by a multicapillary to a spot with radius of 150 µm. The apparatus thus allows measurements of very small samples or scanning of the sample in two directions getting a two-dimensional map of Mössbauer spectra.

Accessories

1) Potentiostat Origa

Potentiostat Orgiga2000 allows a controlled electrolytic deposition of 57Co films on metallic surfaces. Such electrodeposition is one of the available methods for sample preparation for emission Mössbauer spectroscopy.

Expertize

Evaluation of data from nuclear resonant scattering techniques employing synchrotron radiation

In the course of the collaborations with DESY Hamburg (Germany) and ESRF Grenoble (France), we got expertize step by step in evaluation and interpretation of spectra obtained by nuclear resonant scattering (NRS) methods by using of synchrotron radiation. The nuclear resonant scattering methods, which are sometime called “Synchrotron Mössbauer spectroscopy”, have a few modifications including nuclear forward scattering (NFS), nuclear Bragg scattering (NBS), and nuclear inelastic scattering (NIS). In all cases the synchrotron radiation is utilized as a source of the gamma photons. The incident synchrotron beam is scattered by a resonant medium, because the energy of incident beam is tuned to the energy of nuclear transition. The radiation scattered on the nuclei carries information on their close surrounding. The method offers unique information on the electronic structure through hyperfine interactions and a density of phonon states.

Thanks to high brilliance of the synchrotron radiation, NFS can be utilized particularly for in-situ investigations of fast processes, e.g. phase transformations, crystallization and chemical reactions. On the other hand NIS method allows measurement of phonon spectra within the studied material.