3. Mössbauer spectroscopy One has to make suitable radioactive precursor having sufficiently long lifetime albeit not too long. Such precursors are made applying various nuclear reactions, i.e., either accelerated beam of charged strongly interacting particles or neutrons in conjunction with the suitable nuclear target. Precursors decay and populate nuclear level in question. All meta-stable nuclear states are characterised by the following good quantum numbers: spin I and parity p. Decay schemes suitable for the Mössbauer spectroscopy are shown at the side. Other decays could be used sometimes as well. Sometimes α decays or isomeric transitions are used to populate the resonant level. In some cases a population due to the nuclear reaction is used.

4. The beam emitted from the source could be strongly absorbed in the resonant absorber containing the same nuclei in the ground state. Subsequent decay occurs in random directions and/or it follows via the electron capture. Hence one can expect strong beam attenuation under resonant conditions. However there is serious problem of the nuclear recoil occurring in the source and absorber.

7. Levels for some simple selected case are shown below.

9. Real life spectrometer MsAa-3 produced by RENON Bench for the room temperature measurements. One can see the laser powered Michelson - Morley interferometer used to calibrate the velocity scale, velocity transducer with the collimator hiding source (absorber is attached to the exit window of the collimator) and the proportional detector with the high voltage supply and pre-amplifier. Power supply for the spectrometer, and power supply for the laser are in the background.

10. Details of the resonant beam path are shown below. One can see the front end of the transducer, collimator mounted in the safety ring, proportional detector with the beryllium window and the detector high voltage supply integrated with the charge sensitive pre- amplifier.

11. Front end of the collimator is shown with the attached absorber. A detector is seen from the top.

12. General view of the electronics is shown at the side. One can see the spectrometer central unit, rechargeable battery used as the power supply buffer, and the digital oscilloscope used for the diagnostic purposes.

13. Central unit of the spectrometer is shown with two universal temperature controllers. This unit has two TCP/IP ports 100Base-Tx connecting spectrometer to the Internet.

14. Vacuum oven for transmission geometry measurements on the absorbers. The oven is able to reach 800 °C. See the beam entrance beryllium window.

15. High temperature oven designed for the emission Mössbauer spectroscopy on in- situ oriented single crystal sources maintained under controlled atmosphere and temperature up to 1200 °C. See the bottom part of the transducer with the light frame used to move the reference absorber. The frame surrounds a detector holder. The gas inlet valve and the micrometer screw used to set up internal goniometer are seen at the base of the oven.

17. One of the most important transitions

18. Examples of some spectra

20. Thank you very much for your attention.