Publications

Dosimetry from I-125 emitting Auger electrons in the follicles of the thyroid will improve when their complete interaction with the molecular structure about the Auger emitting atoms is known to Angstrom distances. Extended x-ray absorption fine structure (EXAFS) can provide this information. EXAFS experiments gave intermolecular and intramolecular distance for pure solid L-thyroxine (T-4) (C15H11I4NO4) using a model based on crystalline T-4 hydrochloride monohydrate (C15H11I4NO4HCl.H2O). For a solution of L-thyroxine the structure consists of the intramolecular distances found for T-4 and an additional shell of four carbon atoms distances of 2.01 Angstrom. Atomic density functions from Fourier transformed EXAFS measurements are suitable for estimating very short range interactions of Anger electrons in thyroid thyroglobulin over a radial distance of 7.71 Angstrom. Examination of density functions provided a plausible argument for the difference in biological effect between I-131 and I-125 in the thyroid.

The paper presents the current density peaks during the heating-up phase for different kind of quartzes: clear natural from Brazil, smoky natural, and synthetic quartz from Sawyer Research Product (Electronic and Premium Q), Toyo, romanian and polish ones, and compares the phenomenon in vacuum and in air for the same applied electric field and gives a model, with which the process could be described.

Laser spectroscopy has been applied to systematically investigate the effect of MgO or ZnO codoping on the Nd3+ centres formed in LiNbO3. Both codopant oxides produce the same effect, so two new Nd3+ centres appear in both LiNbO3(MgO):Nd and LiNbO3(ZnO):Nd crystals. These new centres correspond to a small percentage (less than 1%) of Nd3+ ions, which are displaced from Li+ sites to a new lattice site. The possible sites for these Nd3+ centres are discussed.

A new model for the medium-range order in amorphous hydrogenated silicon is proposed that qualitatively explains a variety of experimental data. The model consists of a packing of continuous random network domains separated by distorted interfaces accumulating dangling and hydrogenated bands and hydrogen clusters.

The intensity dependent complex character of the photodarkening of virgin As2S3 samples exposed to continuous wave (CW) and pulsed laser radiation has been measured. Excitation in the CW and pulsed (picosecond) regime for the same irradiation doses leads to significant differences in the photodarkening curves. It is shown that the kinetics of the photodarkening can be decomposed into several processes related to structural transformations in As2S3: defect elimination and stabilization, polymerization of the structural entities, decomposition followed by arsenic clustering and arsenic oxidation.

Several cuprates of type Pb-0212 are prepared. The crystal structure is refined from neutron powder diffraction and X-ray diffraction data as tetragonal (space group 14/mmm). interestingly, Pb is simultaneously present in two atomic positions with CN 8 and 9 and considered as Pb4+ and Pb2+ Superconductivity with T-c between 30 and 75 K is observed in the system Pb0.5La1.5-xSr1+xCu2Oy. However, in as-prepared powdered materials the superconducting volume fraction remains low due to the formation of grain boundaries acting as weak links, whereas a significant improvement is obtained in bulk materials by use of flux. Mossbauer and susceptibility measurements of Fe substituted materials indicate the development of a spin glass like behaviour at low temperatures.

Models for Al-TM (TM is transition metal) quasicrystals consisting of networks of icosahedral units have the merit to be specific about the transition metal surrounding. Experimental arguments are brought for the importance of local stable Al(12)TM clusters in the formation of disorder-free icosahedral phases.

The intermediate-range order (IRO) in silica gels is investigated by X-ray diffraction and infrared absorption. The IRO degradation in fresh gels with respect to v-SiO2 and its recovery upon annealing are quantitatively characterized.

Thermal analysis of a pyroelectric bimorph structure, performed for a sinusoidally modulate heat flow, reveals the possibility to obtain a larger signal than in the case of a homogenous pyroelectric structure. The ratio between the signal generated from a bimorph structure and the signal generated from a homogenous structure, in the same conditions, depends on the material properties and on the modulation frequency. This ratio, computed for a particular bimorph, is up to four at 1000 Hz.