Methode de mesure de la periode d'un corps radioactif de courte vie application au179m Hf et au46m Sc

The decay curve of short-lived radioisotopes (T<1 min), if registered by a multichannel analyzer in multiscaler mode, does not remain exponential when the counting rate increases. A method for adjusting experimental values by the maximum of likelihood function is proposed. It includes the determination of initial dead-time fraction. The half-lives of^179m Hf and^46m Sc determined by the present method show a good concordance with table data, for initial dead time fractions as high as 80%.      

The half-lives of 90mY and 97Ru

In an attempt to improve the accuracy of neutron activation analysis, gamma-ray spectrometry and least-squares methods developed for other nuclides have been applied to redetermine the decay constants of ^90mY and ⁹⁷Ru. Several irradiated samples of each pure element were counted continually through several half-lives, acquiring up to 100 spectra with good statistics. Photopeaks from each nuclide were evaluated with a region of interest integration routine, and each data point corrected for rate-related losses before fitting to an exponential function by a nonlinear least-squares procedure. The half-lives found are 3.204 ± 0.008 h for ^90mY and 2.836 ± 0.014 days for ⁹⁷Ru, where the uncertainty is an estimate of the 95 % confidence level. Although (by Chi squared criteria) the fits to the decay curves were very good and the uncertainty of the resulting half-lives an order of magnitude smaller than the previously published uncertainty, care is necessary before assigning a best value with a totally defensible uncertainty to the overall data set.     

Spontaneous fission in the heavy elements

Investigations of mass and kinetic-energy distributions from spontaneous fission have been extended in recent years to an isotope of element 104 and, for half-lives, to an isotope of element 108. The results have been surprising in that spontaneous fission half-lives have turned out to be much longer than expected and mass and kinetic-energy distributions were found to abruptly shift away from those of the lighter actinides, showing two modes of fission. These new developments have caused a re-evaluation of our understanding of the fission process, bringing an even deeper appreciation of the role played by nuclear shell effects upon spontaneous fission properties.     

Influence de la Structure de Diverses Fonctions sur l'Evaluation de l'Energie de Correlation

The influence of various correlation functions, multiplying the monoelectronic space function, is studied and applied to the Helium atom and its isoelectronic series. We used Slater-type basis orbitals and the ground and first excited states have been studied, taking into account the virial and cusp conditions. In the ground state, a very good value for the correlation energy is obtained, using a function of the type For the excited states, this type of function overestimates the assumed value of the correlation energy.     

Le dosage de traces de cuivre dans l'arsenic tres pur par activation neutronique

The determination of traces of copper (<p.p.m.) in arsenic is impossible by non-destructive γ-spectrometry because of the similarity in the half-lives and spectra of the two isotopes used. The proposed separation and decontamination of copper are based on the following operations: bromine attack, hydrolysis, precipitation of barium arsenate, anion exchange, separation of copper as sulfide and recovery by electrolysis. Amounts of copper in the range 20–100 ng can be determined.     

Contribution à l'étude Électrochimique de Dérivés de l'Acide Mercapto-2 Pyridinecarboxylique-5. II

Abstract

Electrochemical caracteristics of 2-mercaptopyridine-5-carboxylic acid and its methylic ester have been determined using recent polarographic techniques. Measurements have been carried out as a function of parameters such as frequency, others surimposed signals and as a function of concentration and pH. Results are compared to those obtained for selectively methylated on sulfur or nitrogen atoms derivatives. Interpretations of the data are given. The optimal conditions for a quantitative determination by D.C. and differential pulse polarography are fixed.     

Influence de l'oxygène sur la conductivité électrique du fluorure de baryum monocristallin

The influence of oxygen on the electrical properties of single crystals of BaF₂ was investigated in the temperature range 450–1150°C. Two types of studies have been undertaken: total ac conductivity and cation transport measurements. The results confirm an anion Frenkel disorder model in MeF₂. Substitution of the fluorine atoms by oxygen in the lattice supposes the creation of the vacancies V^·_F. The evaluation of intrinsic, extrinsic and association domains as a function of oxygen partial pressure has been studied. Values for the energy of formation of the intrinsic defects, the motion energies of V^·_F-vacancies and association or precipitation energy have been deduced from the slopes of the conductivity curves.     

Tables of gamma rays emitted by radionuclides produced through photonuclear reactions

The tables have been prepared as an auxiliary for the interpretation of results in photoactivation analysis. They include data concerning the disintegration of radionuclides produced by (γ, n) reactions on all stable isotopes with a relative abundance greater than 1% and by (γ, p) reactions on elements withZ≤39. The γ-rays are listed in ascending order of the energies; half-lives, intensities and other useful informations are also included.     

Étude de la transition conformationnelle de l'acide polyacrylique syndiotactique en solution aqueuse par spectroscopie de vibration

The Raman and infrared spectra of syndiotactic polyacrylic acid have been investigated as a function of neutralization, in aqueous solution. The acid and its sodium salt have a planar zig-zag configuration. The progressive shift of the Raman line assigned to the vibration mode v(C-COOH) between 20 % and 50 % neutralization indicates a conformational transition from the degree of ionization α = 0.2. The absence of hydrogen bond of the unionized and partially ionized acid is corroborated.     

Aspect energetique de l'agregation des tensioactifs cationiques

The critical micelle concentrations and the enthalpies of micellization of alkyltrimethylammonium bromides having dodecyl, tetradecyl and hexadecyl hydrocarbon chains have been studied using surface tension and calorimetry measurements as a function of temperature. As expected, the change of critical micelle concentrations is very small with an increase of temperature of 10 deg whereas we observe a drastic change of the enthalpies of micellization. As it has been found by applying the Van't Hoff law to thecmc values at different temperatures, the calorimetric measurements show that the enthalpy of micellization, exothermic above a minimal temperature, becomes endothermic below this temperature.     

Synthese de polymeres a proprietes pharmacologiques: Introduction de sequence peptidique en chaine laterale

Amino acids have been introduced on to the side-chains of a polymer. Two schemes have been studied: the first involves the synthesis of a monomer containing the amino acid drug moiety and subsequent polymerization; the second depends upon chemical modification of a polymer with the amino acid drug moiety. The drugs used in this study are steroids (cholesterol testosterone). The amino acid moieties introduced on to the side-chains are L-lysine. The preparation of the drug containing the amino acid is done by reacting the chloroformate derivative of the steroid with the amine function of the lysine subsequent to the blocking of the amino acid as a copper complex. The methacrylic monomer is obtained by reacting methacryloyl chloride with the drug amino acid moiety. The polymers were characterized by i.r., NMR (¹H and ¹³C) and GPC. Pharmacological tests are being performed to observe the effect due to the hydrolysis of the drug or the amino acid drug in living organisms.     

Influence des conditions experimentales du depot de SiC par RCVD sur l'infiltration de substrats de carbone poreux

The infiltration by SiC of porous substrates of carbon or graphite powders by reaction between the substrate and an SiCl₄-H₂ gaseous mixture has been studied by the reactive chemical vapor deposition (RCVD) method as a function of temperature gaseous mixture composition and total flow rate. β-SiC has been characterised using ESCA spectroscopy, X-ray diffraction and chemical analysis with MASE spectroscopy. The silicon carbide is present throughout the sample. The growth rate of the SiC layer is very slow and the activation energy of the process is evaluated at 168 kJ mol⁻¹. High temperatures (1430 °C) and flow rates (950 cm³ min⁻¹) promote the deposition on the surface of the sample and the correct orientation of the crystals. The presence of whiskers has also been detected in the pores of the substrates.     

Polymeres porteurs de greffons peptidiques: Polymérisation et copolymérisation de monomères styréniques parasubstitués par des oligopeptides

Polymers and copolymers with peptide pendant chains have been prepared by polymerization and copolymerization of styrene with para styryl peptide monomers terminated by a carboxylic acid or primary amine group.

Polymerizations of I and II have been initiated by AIBN, in tetrahydrofuran or N,N-dimethylformamide. For polymers with functional ends on side-chains protected by urethane functions (amino group) or ester function (acid group), polymer regeneration has been carried out by acidolysis (urethane) and basic hydrolysis (ester). The influences of monomer structure on polymerization yield and the water solubility after neutralisation, have been considered. Copolymerizations of styrene with I and II have been studied. Random copolymers, with solubility in various solvents depending on their composition, have been obtained. Reactivity ratios have been determined.     

Reevaluation of the half-lives of87mSr,90mY and109mPd

The half-lives of^87mSr,^90mY and^109mPd have been determined more accurately, as compared to previous measurements.     

Spectres de vibration de pigments rouges de la famille des quinacridones

The i.r. and Raman spectra of various crystalline phases of the trans linear quinacridone and some methylated and chlorinated derivatives have been investigated between 4000 and 200 cm⁻¹. Each of these pigments has been characterized spectroscopically and an assignment for intramolecular fundamentals is given in terms of group frequencies. The strength and length of NH ⋯ O hydrogen bonds have been assessed from the vNH frequency and correlated with the pigment colour which is principally determined by intermolecular interactions rather than by the substituent hypso(batho)chromic effect. The NH ⋯ O distance increases from 2.87 Å for the red compounds to 2.93 Å for the purple ones.     

Kinetic resolution of atropisomeric amides

We have demonstrated the feasibility of the kinetic resolution of atropisomeric amides using the commercially avaliable AD-mix. To our knowledge, this methodology represents the first catalytic kinetic resolution of such compounds. Relative rates of up to 32 have been found for the kinetic resolution processes. We have also determined the barriers to rotation and half-lives of some of these amides. The half-lives range from 7 to 135 h at room temperature.     

Reactivite des β-cyclopropyl α-enones—II : Etude de l'addition des diorganocuprates

The lithium dimethylcuprate addition on six substituted bicyclo[3.1.0]hex-3-en-2-ones was studied. For five ketones, both expected 1,4-addition compound and 1,6-addition compounds are obtained. The last products result from a cyclopropane bond cleavage. There is no evidence for a correlation between the radical anion half-lives and the formation of ring opened compounds. In many case, the broken bond is different from that which is concerned in the reduction by solvated electrons in liquid ammonia. So the 1,6-addition products do nor probably arise through an electron transfer mechanism. However, a nucleophilic attack of the substrate by a copper atom followed by a reductive elimination inside the complex can be supposed; then both the nature and stereochemistry of reaction products can be explained.     

Precise determination of half-lives of56Mn,193Os and197,199Pt

The half-lives of⁵⁶Mn,¹⁹³Os and^197,199Pt have been remeasured with better precision compared to previous valeus.     

Natural depuration rate and concentration of cesium-137 radionuclide in Black Sea macro algae

Cesium-137 concentrations in red, brown and green algae have been studied for the calculation of natural depuration rates. The algae species were collected from the same population of the Black Sea stations during the period of 1986–1995. The natural depuration rates are estimated as biological half-lives. The pattern of depuration results represented by a single component for each algae division. The biological half-lives of¹³⁷Cs in red (Phyllophora nervosa), green (Chaetomorpha linum) and brown (Cystoceira barbata) algae are estimated to be 18.5, 21.6 and 29.3 months, respectively.¹³⁷Cs and⁴⁰K activity levels and their ratios in algae species in two stations in Black Sea region of Turkey have been determined during the period of 1990–1995. The results showed that the Sinop region was more contaminated than the ile region on the Black Sea coast of Turkey from the Chernobyl accident.     

Etudes d'Hétérocycles Pentagonaux Polyhétéroatomiques par RMN du 13C. Effets de Substituant,de la Benzocondensation et Etude de la Tautomèrie Prototropique en Série Benzothiazolique

The ¹³C NMR spectra of 43 benzothiazoles have been recorded in DMSO-d₆. All carbon atoms have been attributed in an unambigous way owing to substituent effects in position 4, 5, 6 or 7. We discuss variations of chemical shifts as a function of the nature of the substituent in position 2 (equation of type: Δδ = aF+bR+cQ+d′), annelation in the benzoheterocyclic series, and prototropic tautomerism in the benzothiazolic series (in the case of the substituent in the 2-position being an OH, SH or NHR group).