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The accidental coincidences of a measuring system based on time-to-amplitude conversion are considered in some detail for the case of low starting and high stopping rates. Two types of accidental coincidences are distinguished, those carrying time information and those without time information. Neglecting any deadtime effects of the detectors, analytical expressions for the calculation of the time distribution of the random coincidences are evaluated. The analytical expressions have been confirmed by Monte Carlo simulations. The procedure is applied to time-differential Mossbauer spectroscopy in order to extract the time spectra of true coincidences. The measured spectrum in a time channel turns out to be a superposition of the true spectrum (true coincidences), a time integral spectrum (random coincidences), and a weighted superposition of true spectra of other time channels (random but time carrying information). A measurement with a single line 57 Co/Rh-source and single line K[Fe(CN) 6 ]·3H 2 O-absorber with stopping rates of 1 MBq shows agreement between the theoretical time-filtered spectra and the corrected measured spectra of true coincidences.

Increasing attention is being paid to non-conventional Mossbauer methods in view of the extension of Mossbauer Spectroscopy (MS) to a broadening field of applications. With such long-lasting experiments the shortening of the measuring time required for a given statistical significance is of major practical importance. It is shown that the statistical utility rateu allows one to determine which experimental parameters have a primary role, and it also enables sucessive optimization. It is pointed out for various MS measurements that the strategy for improving the experimental performance is strongly dependent on the given problem. As examples, time-differential Mossbauer measurements and conversion electron Mossbauer spectroscopy are discussed.

After effects following nuclear transformation have been extensively studied in a large variety of matrices by Mossbauer Emission Spectroscopy (MES). The branching ratios of transient atomic charge states and energetically unstable states of the environment, excitations of electronic ligand field states and populations out of equilibrium within the electronic ground state manifold have been studied. Recent developments and also new insights and understandings of different aspects of the aftereffects of radioactive decay of57Co in semiconductors and molecular crystals are reviewed. A detailed picture of the decay process within the electronic states of the nucleogenic Fe3+ species could be obtained from emission spectroscopy of sources in applied magnetic fields.

Using our new spectrometer for time-differential Mossbauer emission spectroscopy we reinvestigated the high-spin→low-spin relaxation following the57Co(EC)57Fe process in [57Co/Co(phen)3](ClO4)2 (phen=1,10-phenanthroline). In contrast to former investigations we found a temperature dependent initial population less than 1 for the metastable high-spin states. The results and the data evaluation method are presented.

The population of anomalous spin states and aliovalent charge states of iron induced by the 57 Co(EC)57 Fe nuclear decay in polycristalline transition metal compounds was studied by means of Coincidence Mossbauer Emission Spectroscopy (CMES), that is Time-Differential Mossbauer Emission Spectroscopy (TDMES) as well as γ/Xray-Coincidence Mossbauer Emission Spectroscopy (γ/X-CMES). By use of time-integral Mossbauer emission spectroscopy (TIMES) we have observed anomalous high spin (S = 2) states of 57 Fe(II) in the system [57Co/Co(phen)3(ClO 4)2 with increasing intensities on lowering the temperature. With TDMES we followed quantitatively the high spin-low spin relaxation kinetics in this compound.

A new spectrometer for time-differential Mossbauer spectroscopy was developed featuring high count rate capability, good time resolution, and flexible data handling.

The photoelectron conversion efficiency of NaI(Tl) detectors has been measured by counting single photoelectron pulses of the detector output pulse train on a very fast storage oscilloscope. This result is compared with those obtained by the measurement of the achievable time resolution using the first photoelectron triggering technique.

A high-efficiency, high rate-capability, computer-based measuring setup for Time-Differential Mossbauer Spectroscopy was constructed. Applying NaI(Tl) and plastic scintillators for the detection of the 14.4 keV and 122 keV γ-radiation respectively, a superior timing (2, 3 ns FWHM) was achieved by a “fast-fast-ultra fast” timing method developed for that purpose.

A spectrometer for time-differential Mossbauer spectroscopy was developed with a high count rate capability, a good time resolution, and a flexible data handling. Chemical and physical aftereffects following the57Co decay were studied within the cobalt doped systems Turnbulls blue and ZnS.