Simultaneous determination of trace uranium and thorium by radiochemical neutron activation analysis

A method for the simultaneous, radiochemical neutron activation analysis of uranium and thorium at trace levels in biological materials is described, based on a technique known as LICSIR, in which a double neutron irradiation is employed. In the first, long irradiation²³³Pa (27.0 d) is induced by neutron capture on²³²Th and then the sample is cooled for several weeks. A second short irradiation to induce²³⁹U (23.5 m) is followed by a rapid sequential radiochemical separation by solvent extraction of²³⁹U with TBP and²³³Pa with TOPO. Chemical yields of²³⁹U and²³³Pa were measured for each sample aliquot using added²³⁵U and²³¹Pa tracers from the -spectra of the separated fractions. The technique was validated by quality control analyses.     

Pyridinium o-iodoxybenzoate as a Safe form of a Famous Oxidant

The stable pyridinium salt of o-iodoxybenzoic acid (PIBX) that is easy to obtain can serve as a convenient substitute of IBX as an oxidant. PIBX is safer, has neutral properties behaves as an equivalent to IBX in the oxidation of alcohols to ketones or aldehydes in polar solvents (DMF, DMSO), and provides higher oxidation rate in THF due to better solubility.     

Unprecedented conversion of triethylamine and disulfur dichloride into a thienopentathiepin and a heptathiocane

[reaction: see text] In a remarkable cascade reaction, triethylamine is converted into the thienopentathiepin 2a and the heptathiocane 3a by a preequilibrated solution of disulfur dichloride and DABCO in chloroform.     

The leachability of some natural and man-made radionuclides from soil and sediments on acid attack

A radiotracer study was made of the leachability of some natural and man-made radionuclides from soils and sediments subjected to attack by various acid mixtures. Particular attention was paid to the nuclides²³⁸U,²³²Th, Pa (as²³³Pa) and Np (as²³⁹Np), since for these neutron activation can be used to study recoveries and/or to induce in situ radionuclides in samples. Thus conventional NAA allowed determination of total²³⁸U and²³²Th instrumentally, and also enabled analysis of leachates and residues by radiochemical or instrumental NAA. Activation of these nuclides produced samples endogenously labelled with²³³Pa and²³⁹Np whose behaviour on acid dissolution/leaching could be examined. Furthermore, comparison of neutron irradiated and non-irradiated samples allowed us to investigate the possibility of increased leachability induced by nuclear recoil reactions; however, this effect was negligible. We also investigated the acid leaching of americium adsorbed on the surface of sediment. In general, unsatisfactory leaching recoveries were found for²³³Pa,²³⁹Np and²³²Th for most materials, indicating the need for total dissolution procedures.     

Kinetics and mechanism of glycolide and ethylenoxalate copolymerization. Characteristics of the copolymers formed and mechanism of the biodegradation

The study of glycolide (GL) and ethylenoxalate (EO) copolymerization with the use of SnCl₂ 2 H₂O as a catalyst was carried out by ¹H NMR spectroscopy. Monomer reactivities are found to be close and equal to 1,1 and 1,11 for GL and 0,71 and 0,85 for EO at 150 and 170 °C, respectively. Kinetic data obtained show that the reaction proceeds without induction period up to entire consumption of every monomer. The detailed identification of ¹H spectra enables to follow the polymer microstructure in the course of copolymerization. Thermal properties of copolymers and their biodegradation abilities have been studied. The biodegradation rate is shown to increase with growing EO proportion in the copolymer. The lactone biodegradation mechanism where the electrophility of carbon and nucleophility of OH group are playing the most important role, is suggested. The correlation between the biodegradation rate and the chemical shift in ¹³C NMR spectra of the carbon atom of the carbonyl group has been established.     

Evaluation of measurement uncertainty in the determination of 210Pb and 210Po using beta counting and alpha spectrometry

 Measurement uncertainties in the determination of ²¹⁰Pb and ²¹⁰Po in Reference Material IAEA-300 (Baltic Sea Sediment) were evaluated. ²¹⁰Pb and ²¹⁰Po were separated from the matrix using an Sr resin column. The chemical yield of ²¹⁰Pb was determined gravimetrically in PbSO₄ form. Precipitation was followed by beta proportional counting after ²¹⁰Bi ingrowth. ²¹⁰Po was determined by alpha spectrometry after its spontaneous deposition on a Cu planchet. The major source of uncertainty was identified as the statistical counting uncertainty, which was also expected and is almost impossible to reduce without extension of the time required for an analysis. The expanded uncertainties were determined as 7.4% and 12.2% for ²¹⁰Pb and ²¹⁰Po, respectively. Received: 3 September 2002 Accepted: 3 December 2002 Acknowledgement This work was financially supported by Ministry of Education, Science and Sport, Republic of Slovenia (Project group PO-0106–0532). Presented at CERMM-3, Central European Reference Materials and Measurements Conference: The function of reference materials in the measurement process, May 30–June 1, 2002, Rogaška Slatina, Slovenia Correspondence to P. Vreˇcek     

Two-phase model of hydrolysis kinetics and its applications to anaerobic degradation of particulate organic matter

The various equations of hydrolysis kinetics included into the generalized simulation model (METHANE) were tested on the anaerobic digestion of cellulose, sludge, and cattle manure. The good agreement between the model simulation results and experimental data was obtained. The Contois equation, taking into account a hydrolytic biomass, and the firstorder equation with respect to the particulate substrate only, were shown to be the approximations of two-phase hydrolysis kinetics.     

Development of a method for the determination of 226Ra by liquid scintillation counting

Liquid scintillation counting has not been widely applied to a-particle detection because of its poor energy resolution and variable background. In the present work, a time saving and reasonably accurate method for determination of ²²⁶Ra in water has been developed, using liquid scintillation spectrometry and pulse-shape analysis. The effect of three levels of chemical quench on the spillover of alpha interactions into the beta window and vice versa was assessed. The advantages of liquid scintillation in comparison with other methods (radon emanation) for determination of ²²⁶Ra are the high counting efficiency (~100%) and the easier sample preparation, with no need for sample preconcentration.     

Phonon-Assisted Tunneling Current in a Double-Barrier Heterostructure with a Quantum Well

Journal of Russian Laser Research - Based on a quantum-mechanical model with a non-Hermitian Hamiltonian, we theoretically describe the tunneling current in a heterostructure containing a quantum...