Ts. Bonchev

Mössbauer parameters of the two long-lived metastable states in Na2[Fe(CN)5NO]·2H2O single crystals

We have measured the quadrupole splitting, isomer shift and line broadening of the ground and two metastable states in Na2[Fe(CN)5NO]·2H2O single crystals. Pure state II could be observed by Mössbauer spectroscopy after irradiation of state I with light in the near infrared spectral region. The difference between the two nearly infinitely long-lived electronic states is shown. A possible change of the Fe(3d, 4s, 4p) electron densities is discussed on the basis of the Mössbauer parameters and thev(FeN) andv(NO) stretching vibrations. The resulting new orbital population allows to explain the observed properties of state I. A rearrangement of the electron density due to state II would lead to a contradiction with the vibrational behaviour of the molecule. The larger line width of both metastable states could not yet be interpreted.

Depth selective Mössbauer spectroscopy: II. Influence of the atomic number of the inert component in the surface layer

Abstract A new variant of an empirical method for defining the distribution of a Mossbauer element in the depth of a surface layer with the help of depth selective Mossbauer spectroscopy (DSMS) is described in the present paper. The influence of the atomic number of the inert (not Mossbauer) substance on the deformation of the conversion electron spectrum is considered and accounted for.

Depth selective Mössbauer spectroscopy: I: A study on some processes connected with the passage of low energy electrons through matter

Abstract The present paper deals with some phenomena concerning the passage of low energy electrons (LEE) through matter. This process is connected with the problems of depth selective Mossbauer spectroscopy (DSMS). The influence of the atomic number of the absorber on the deformation of the conversion electron spectra is considered. The influence of the absorbers crystal structure and the applied electric field on the sample has also been investigated.

Observed difference between the probabilities of recoilless resonance absorptionf′ and reemissionf″ of gamma-quanta in single crystals of Na2[Fe(CN)5NO]·2 H2O

The recoilless absorption probability factor,f′, and recoilless reemission,f″, both measured on Na2[Fe(CN)5NO]·2 H2O single crystals using the “black” filter technique, were found to be different. Unexpectedly, the results found weref″>f′. In the calculation off″, selfabsorption in the scatterer, non-ideality of the “black” filter and the influence of non-resonant scattering processes have all been taken into account. By varying the scattering geometry for the incoming and outgoing γ-beam relative to the crystallographic axes only a change in the reemitted valuesf″a, f″b, f″c could be detected because of the long lifetime of the excited nucleus (∼10−7 s) relative to the lattice vibration frequencies (∼1012 Hz).

Investigation of the Mossbauer line fine structure of a new α2-Sn allotropic form

A fine structure of the Mossbauer line of the new alpha 2-Sn allotropic form has been observed. The isomeric shifts of five alpha 2-Sn substructures have been determined. The Mossbauer data have been considered together with X-ray diffraction ones. It is shown that the isomeric shift increases when the lattice parameter of alpha 2-Sn substructure decreases. Magnetic measurements of the susceptibility of samples containing a significant quantity of alpha 2-Sn have been carried out. The problem with the alpha 2-Sn isomeric shift interpretation has been discussed. Considerations have been given to the causes of the formation of the new crystalline structures.

Application of the mössbauer effect to microgram samples with resonance sample scintillators

Abstract The possibilities of the Mossbauer effect for qualitative and quantitative measurements of microgram amounts of resonance absorbing matter are considered. The sample is placed in a plastic scintillator and the conversion electrons emitted are measured. The preparation of the resonance sample scintillators (RSS) and the methods of measurement are described in detail. Mossbauer spectra of different samples containing SnO 2 are given as an example. The sensitivity of the method is around 10 -7 g (even less in some cases). A concentration of 4 · 10 -6 % SnCl 2 in aqueous solution can be measured. The methods can be used for surface studies of small particles.

Methods of determining the recoilless absorption probability of Mössbauer radiation: Part I — Use of conventional detectors

Abstract This article treats a method of determining the recoilless absorption probability of Mossbauer radiation with the use of a control absorber. By means of this absorber the influence of the background on the value of the Mossbauer effect and on the resonance curve area, measured experimentally, is being eliminated. A method for determining the theoretical values of the effect and the area of the control absorber, as well as the results of the experimental check-up of the method for CaSnO 3 are also described. The value, obtained for f ′=0.574±3% confirms someof the results given in the literature.

On the phase and structural composition of electrochemically obtained tin samples

Data on phase and structure compositions of tin samples obtained by electrochemical reduction of aqueous solutions of SnCl2.2H2O with Mg are presented. Studies have been carried out by transmission Mossbauer spectroscopy with a thin resonance scintillation detector. The resulting spectra have been processed by a step-deconvolution procedure, which provides exceptionally high velocity resolution.

An attempt to investigate the influence of the chemical binding on the total mass absorption coefficient of gamma quanta with the Mössbauer effect

Abstract An attempt to investigate the influence of the chemical binding on the total mass absorption coefficient (μ/ϱ) t , as predicted by a number of authors, is performed. The absorption coefficient is determined for the recoilless part of the resonance gamma radiation of 119 Sn i . This permits total elimination of the background and considerable increase of the accuracy of measurement as compared to the other existing methods.

On the observation of anomalous electron emission from a thin film under the influence of an outside electric field

SummaryIt is established that accelerated secondary electrons with very low energies emitted from a thin surface layer where Mössbauer absorption and normal photoeffect are taking place show two distinctly separated energy lines. The maximum of the first line corresponds to the applied accelerating voltage while that of the second one corresponds to about 30% higher energy. The investigations are performed with a magnetic beta-spectrometer and with an electrostatic analyser. It is found that the intensity of the second, «anomalous» line depends on the nature of the emitting layer. A number of experiments confirming the reality of the observed effects are reported.