3.5 MeV triton activation for elements with Z<34

The sensitivities for the determination of 25 elements from Z=4 to Z=33, using 3.5 MeV triton activation, were calculated from experimentally measured yields for 50 radioisotopes obtained via (t, n), (t, d), (t, 2n) or (t, α) reactions. For an irradiation of 1 hour at 1 μA, the calculated detection limits are better than 100 ppb for B, N, O, F, Na, Mg, Al, Si an S. Because of the Coulomb barrier, triton activation is of considerable interest for non destructive analysis of low Z elements in medium and high Z matrices. Finally integrated activation curves of high sensitivity elements were determined.     

Triton reactions with some light and medium elements. Application to activation analysis

The excitation functions for nuclear reactions induced by tritons are determined up to about 3.5 MeV for some light and medium elements: fluorine, sodium, magnesium, aluminium, silicon, titanium and vanadium. Because of large cross-sections the activation technique was used with thin targets. Then the possibilities of using these reactions to analytical purposes are discussed.     

Contrôle de la pureté d'échantillons de niobium et de tantale par spectrométrie gamma directe après irradiation au moyen de protons de 10 MeV

Non-destructive analysis of samples of niobium and tantalum has been achieved by activation with 10-MeV protons and γ-ray spectrometry. Niobium and molybdenum have been detected and determined in tantalum, as well as molybdenum and tungsten in niobium. Upper limits of concentration have been established for over thirty other undetected elements; most of these limits are below the p.p.m. level, and some reach the p.p.b. level.     

Water waves as a spatial dynamical system; infinite depth case

We review the mathematical results on traveling waves in one or several superposed layers of potential flow, subject to gravity, with or without surface and interfacial tension, where the bottom layer is infinitely deep. The problem is formulated as a "spatial dynamical system," and it is shown that the linearized operator of the resulting reversible system has an essential spectrum filling the real line. We consider three cases where bifurcation occurs. (i) The first case is when, in moving a parameter, two pairs of imaginary eigenvalues merge into one pair of double eigenvalues, and then split into four symmetric complex conjugate eigenvalues. (ii) The second case is when one pair of imaginary eigenvalues meet in 0, and disappear; (iii) the third case is when the phenomenon described in (ii) is superposed to the presence of another pair of imaginary eigenvalues sitting at finite distance from 0. We give a physical example for each case and more specially study the solitary waves and generalized solitary waves, emphasizing the differences, in the methods and in the results, between these cases and the finite depth case.     

Pseudo-steady-state solutions for solidification in a wedge

Polubarinova-Kochina's analytical differential equation methodis used to determine the pseudo-steady-state solution to problemsinvolving the freezing (solidification) of wedges of liquidwhich are initially at their fusion temperature. In particular,we consider four distinct problems for wedges which are: freezingwith the same constant boundary temperature, freezing with thesame constant boundary heat fluxes, freezing with distinct constantboundary temperatures and freezing with distinct constant fluxesat the boundaries. For the last two problems, a Heun's differentialequation with an unknown singularity is derived, which in bothcases admits a particularly elegant simple solution for thespecial case when the wedge angle is . The moving boundariesobtained are shown pictorially.     

Analyse d'echantillons de cobalt par spectrometrie gamma directe apres irradiation au moyen de protons de 10 mev

Proton activation is applied to the analysis of cobalt samples; 41 elements were only occassionally detected. For the other elements, detection limits were irradiation with 10-MeV protons. Samples from two commercial Companies were analysed: Fe and Cu were always detected, while Ca, Ti, Cr, Zn, As, Se and Mo were only occasionally detected. For the other elements, detection limits were calculated; 33 limits are below the part per million level.     

Résonance 1 : 2 pour les champs de vecteurs réversibles1 : 2 resonance for reversible vector fields

We study the 1:2 resonance for reversible vector fields in $\text{R}{}^4$, depending on a parameter μ and we show the bifurcation of two families of periodic solutions and of two reversible solutions which are homoclinic to some of the periodic solutions belonging to one or the other of the previous families, depending on the sign of a coefficient. To cite this article: M. Barrandon, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 7–10