Conversion Electron Mössbauer Spectroscopy
   HOME

TheInfoList



OR:

Conversion electron Mössbauer spectroscopy (CEMS) is a
Mössbauer spectroscopy Mössbauer spectroscopy is a spectroscopic technique based on the Mössbauer effect. This effect, discovered by Rudolf Mössbauer (sometimes written "Moessbauer", German: "Mößbauer") in 1958, consists of the nearly recoil-free emission and a ...
technique based on conversion electron. The CEM spectrum can be obtained either by collecting essentially all the electrons leaving the surface (integral technique), or by selecting the ones in a given energy range by means of a beta ray spectrometer (differential or depth selective CEMS). This method allows the use of simple and inexpensive detecting equipment, mainly flow-type proportional detectors in which large counting rates can be obtained. This last characteristic makes possible the study of samples with the natural abundance of the Mössbauer
isotope Isotopes are distinct nuclear species (or ''nuclides'') of the same chemical element. They have the same atomic number (number of protons in their Atomic nucleus, nuclei) and position in the periodic table (and hence belong to the same chemica ...
. The information furnished by the integral measurements can be increased by using various angles of incidence or by depositing thin layers of inert material on the sample.


Theory

In the energy range used in CEMS, the incident radiation can interact with the absorber through two kinds of processes: (a) conventional interactions –
photoelectric The photoelectric effect is the emission of electrons from a material caused by electromagnetic radiation such as ultraviolet light. Electrons emitted in this manner are called photoelectrons. The phenomenon is studied in condensed matter physic ...
and Compton effects, and (b) nuclear resonant absorption –
Mössbauer effect The Mössbauer effect, or recoilless nuclear resonance fluorescence, is a physical phenomenon discovered by Rudolf Mössbauer in 1958. It involves the resonant and recoil-free emission and absorption of gamma radiation by atomic nuclei bound in a ...
. Due to conventional interactions the beam is attenuated and electrons are emitted from the sample. The nuclear de-excitation following the resonant absorption takes place by emission of either a
gamma ray A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...
or an internal conversion (IC) electron. In the latter case, the atom is left in an ‘excited’ state with a hole in an inner shell; the energy excess is given away with emission of Auger electrons and/or X-rays. Thus, the electrons emitted from the sample as a consequence of the Mössbauer absorptions are: (a) primary (IC or Auger) electrons originated in the de-excitations of the nuclei excited by the incident beam, and (b) secondary electrons originated by conventional interactions of photons (or resonant absorption of gamma rays) emitted after resonant absorptions.


References


Nuclear Instruments and Methods in Physics Research Bl (1984) 70–84
Mössbauer spectroscopy Instrumental analysis {{spectroscopy-stub