Contact-limited conduction in V2O5P2O5 glasses

The electrical properties of V₂O₅P₂O₅ glass-electrode interfaces have been investigated. Gold, graphite and aluminium, in that order, form contacts of increasing resistance. The dependence of barrier height on the work function of the electrode material is not consistent with the concept of Schottky barriers at the interfaces. The phenomenon may be explained by the downward bending and filling of a narrow band normally situated in the vicinity of the Fermi level, caused by injection of electrons from the less noble metals. This gives rise to a surface layer, which can, in principle, be insulating. However, alternative mechanisms, in the case of the investigated glasses most probably a Poole-Frenkel type field enhanced conduction via separated traps, lead to finite interface resistance.     

The effect of magnetic structures on the electrical resistivity of thulium

The influence of the magnetic structures in thulium with the residual resistance ratio (RRR) of 140 on the electrical resistivity was determined from 4·2 K up to 70 K. The measurements indicated the Néel temperatureT _N = 57.5 K and the Curie temperature T_C = 32 K. Furthermore, a new transition was found at T_H = 49 K which did not appear in the neutron diffraction measurements.Dedicated to Dr. Svatopluk Krupika on the occasion of his 65th birthday.We would like to express our thanks to V. Sojeková and H. Bobulská for their assistance in the measurements.     

Temperature dependence of the critical current density in Y-Ba-Cu-O thin films

We present a study of the temperature dependence of the critical currentJ _c of several dc magnetron sputtered thin Y-Ba-Cu-O films on single crystalline SrTiO₃, ZrO₂ and Al₂O₃ substrates. Near the critical temperature T_c it is found thatJ _c(1–T/T_c)ⁿ withn=3 for the SrTiO₃ and ZrO₂ substrates, whilen=1·3 for the Al₂O₃ substrate. The temperature dependence in our samples approximately agrees with standard theories for weak links or with the Ambegaokar-Baratoff equation.     

On a rudimentary model of instability and (2 x 1) reconstruction of Si (001) and (111) surfaces

A recently proposed simple qualitative theory of instability and reconstruction of surfaces of solids exhibiting a certain covalent component of bonding is applied to (2 x 1) Si (001) and (111) surfaces with a possible extension to analogous surfaces of germanium and GaAs (001)., Shockley surface states from the vicinity of the Fermi energy are supposed to play a crucial role in the electron-phonon coupling. For the Si (001) surface the interaction between bridge and dangling bonds causes the dimerization (primary effect) and the buckling distortions to couple. If the latter effect is pronounced, the asymmetric dimer might exist as a stable or metastable surface phase. For the Si (111) surface the Pandey -bonded chain model seems to be a natural candidate for reconstruction from the present simple point of view.     

Rapid determination of131I in environmental waters using a liquid anion exchanger

A rapid and specific method for the determination of¹³¹I in environmental water samples in the presence of some of the most important fission products is described. Radioiodine is separated from acidified water using tri-n-octylamine solution in toluene with dissolved iodine by one-stage static procedure with about 90% separation efficiency and 200-fold volume concentration. After the decolorization of the organic phase with NaOH in methanol, radioactivity of¹³¹I is counted by a toluene base liquid scintillator with a counting efficiency of 70%. The method is simple and enables to determine low radioactivity¹³¹I with a detection limit less than 5 pCi/1 in about 1.5 hrs.     

Airborne plutonium monitoring

Methods of monitoring low plutonium concentration in the inner and outer atmosphere are analyzed and compared. It is shown that monitors based on the gross alpha counting of air filters are not sensitive enough to measure reliably plutonium activities below 1 MPC. A spectrometric discontinuously operating monitor using a gridded ionization chamber and a membrane filter having 70 cm² active area is described. Plutonium activities of the order of 0.01 MPC /1 mBq.m^–3/ can be measured by the spectrometer at 1 h sampling and 1 h counting time.     

Sorption of cadmium in some arable and forest soils

The sorption of cadmium labeled with ¹⁰⁹Cd in nitrate form, from aqueous solutions in different horizons of some arable and forest soils was studied under static (batch) conditions. Before sorption, a method of sequential soil treatment was applied, which consist in the consecutive removal of individual soil components by the use of appropriate reagents and procedures. Three sorption isotherms were tested. Kinetic studies showed that the sorption of cadmium is rather rapid and it can be well described by a Freundlich or a linear isotherm, whereas the closeness of Langmuir isotherm to the experimental results is lower. From the different sorption isotherms, it would also be possible to estimate the effect of individual components on the sorption of cadmium in soils. It was found that the untreated soils exhibit the highest sorption and the sorption decreases in the order of untreated > acetate treated > water treated > peroxide treated > dithionite treated soil. Sorption of cadmium increases with the depth of the studied soils disregarding their chemical treatment.This revised version was published online in November 2005 with corrections to the Cover Date.     

Differential thermal analysis of montmorillonite

The paper provides an overview of publications on the DTA of montmorillonites (in the temperature range 20–1100°C), starting with the first experiments of Le Chatelier (1887) and ranging up to the present. Consideration is given to the dehydration, dehydroxylation, amorphization and rehydration of montmorillonite (42 references).     

Semiconductor gamma-ray spectrometry with whole spectrum processing

A new method for evaluation of semiconductor -ray spectra based on factorization of the response operator, a Scaling Confirmatory Factor Analysis (SCFA), is described. A set of common factors, resulting from fundamental photon interactions with matter (full energy peak, Compton continuum, backscattering peak and the residual factor), has been used. The scaling and loading coefficients for the common factors have been estimated by a confirmatory least squares technique of factor analysis. A latent interpolation of modelling coefficients enables to construct a response function in the response operator for an arbitrary energy of the measured spectrum. The analysis of incidental spectral parameters indicates a significant improvement of the whole spectrum processing. A comparison of the SCFA method with the most commonly used peak net area method shows that the former method is 5–10 times more sensitive (depending on interferences).     

Separation of radioiodine by multistage isotope exchange in a heterogeneous liquid system

The separation of radioiodine from water by multistage isotope exchange between iodide and molecular iodine in a heterogeneous liquid system under both static and dynamic conditions has been studied in two model arrangements. Equations were derived which enable the calculation of the theoretical separation efficiency in dependence on both the volume concentration and concentration of the carrier of radioiodide in water. It was found that under the same conditions, the calculated values are in a satisfactory agreement with experimentally determined values of the separation efficiency.