A simple technique for surface labeling of solids with222Rn and its short-lived decay products

A simple radioactive labeling technique is described which is based on a recoil injection of atoms of²²²Rn and its decay products from a²²⁶Ra source into thin surface layers of solids.     

Study of isotope exchange reactions by double labelling

This paper presents the method of double labelling in the study of the kinetics of homogeneous isotope exchange reactions. This method was tested by the determination of the Sn(II)−Sn(IV) exchange rate in hydrochloric acid medium. The system was labelled by the tracer^119mSn [initially in the Sn(IV) state]; when the isotope equilibrium was established, Sn(IV) was again labelled by tracer¹¹³Sn. The separation of Sn(II) and Sn(IV) in the given time of exchange was performed by the extraction of Sn(IV)-hydroxyquinolate into chloroform. The specific activities of the separated components were determined from the ratio of¹¹³Sn and^119mSn activities. The exchange rate was calculated from the time dependence of specific activities. The advantage and possibilities of the method of double labelling in the study of isotope exchange are discussed.     

Radiotracer analysis of the physico-chemical state of trace elements in aqueous solutions

Theoretical and experimental analysis of the open-ended capillary diffusion method for study of the state of trace elements in aqueous solutions is presented. It is shown by theoretical considerations that the use of the discontinuous capillary method of diffusion and the evaluation of single measurements using the classical Anderson-Saddington equation yields incorrect diffusion coefficients if two or more forms of the trace element with significantly different diffusion characteristics are simultaneously present in the solution. A new method for the evaluation of diffusion is suggested, which enables calculation of the abundance of two different forms of a trace element. The method employs a continuous measurement of diffusion combined with computer analysis of the data obtained. Verification of the method is carried out for a particular case using trace radiocerium. The effect of adsorption on the diffusion measurement and interpretation is discussed.     

Investigation of the kinetics of exchange reactions by the method of constant velocity supply of the labelled component into the system

The method of constant velocity supply of the radioactive labelled component into the system was used to study the kinetics of the isotope exchange Tl(I)-hydroxyquinolate-Tl(III)-hydroxyquinolate in chloroform. The second order exchange reaction with a halftime less than 1 min was determined in the range of concentrations 0.2–2·10⁻³ M of both components.     

Assessment of variants of the k–ϵ turbulence model for engine flow applications

This paper is concerned with simulation of the mean flow and turbulence evolution in a model engine and comparison of the behaviour of certain important turbulence parameters, namely the intensity, length scale and dissipation time scale, as predicted by three variants of the k–? model developed for application to strongly compressible flows. The predictions pertain to the axisymmetric, disc-chamber, four-stroke, Imperial College model engine operating at 200 rpm and compression ratios of 3·5 and 6·7. The paper analyses the predicted variations of these parameters during the induction, compression and expansion strokes and identifies the versions that produce the most consistent and physically plausible variations. The significance, to the turbulence evolution, of the ratio of the turbulence dissipation time scale to the time scale of compression/expansion is also discussed. It is concluded that on these grounds the Morel–Mansour and El Tahry versions are, and the Watkins version is not, suitable for engine applications.     

Preparation and application of237U for the study of heterogeneous isotope exchange on an ion exchanger

The possibility of preparation of²³⁷U by the²³⁸U(, n)²³⁷U reaction, realized by irradiation of UO₃ on the microtron, has been verified. The relation between yields for (, n) and (, f) reaction was determined. The activated uranium was separated from fission products by extraction into diethyl ether.²³⁷U was used for the study of the kinetics of heterogeneous isotope exchange in the system aqueous solution of UO₂(NO₃)₂ — ion exchanger Wofatit CA-20 in UO ₂ ²⁺ form. The experimental results were evaluated by a model based on particle diffusion with simultaneous isotope exchange between two uranium forms in the ion exchanger.     

Study of kinetics,equilibrium and isotope exchange in ion exchanger systems

An automatic, rapid combustion method has been developed for the determination of tritium and¹⁴C in singly or doubly labelled organic materials by liquid scintillation counting. The sample is burned in a stream of oxygen. The water formed and its tritium content are retained from the gas stream in an absorber containing a small amount of diethyleneglycol monoethyl ether. Radioactive carbon dioxide, if included in the combustion products, is transferred into 3-methoxypropylamine. The final solutions ready for counting are obtained in less than three minutes. Quantitative collection recoveries for both tritium and¹⁴C are achieved and no cross-contamination occurs.