Dosimetrie et spectrometrie approchees de neutrons de fission et thermonucleaires a l'aide de detecteurs visuels plastiques

Abstract

On donne les caractéristiques et le schéma d'un dosirnètre individuel à neutrons, utilisant les détecteurs visuels plastiques, makrofol et nitrate de cellulose, pour l'enregistrement des produits des réactions a seuils (n, f) et (n, α). Le spectre d'énergie analysé s'échelonne entre l'énergie thermique et 20 MeV environ.

Des réactions (n, p) (protons de recul) sont actuellement à l'étude en vue d'obtenir une précision accrue sur la détermination du spectre de neutrons, dans le domaine des énergies de résonance et jusqu'à une centaine de KeV.

Characteristics and the scheme of an individual neutron dosimeter are presented. The principle of the dosimeter is based on (n, f) and (n, α) threshold reaction track visualization in solid state detectors; especially makrofol and cellulose nitrate. The analysed energy spectra is between the thermal neutron energy and about 20 MeV.     

Photolyse Des (Oxo-3)-Butyl-α et β-D-Mannopyranosides

Abstract

(3-Oxo)-butyl mannopyranosides undergo Norrish type II photocyclization giving hydroxyspiroketals of which the structures have been established by NMR spectroscopy and X-ray analysis. The influence of the anomeric and C-2 configurations have been studied and compared to the gluco derivatives. The favored photocyclization of β-mannoside occurs with retention of configuration and that of α-mannoside with inversion of configuration.     

Tailoring silicon radiative properties

We study several schemes to enhance the emission of radiation of silicon surfaces in the infrared. First, we investigate the emission pattern of microscale lamellar gratings ruled on doped silicon which is substantially modified due to the excitation of surface plasmons. In addition to their remarkable spectral selectivity, those sources emit 50% more than a plane interface of bulk doped silicon. An interferential antireflection system similar to a Salisbury screen is also considered. This broadband emitter allows a significant enhancement of the total emitted power compared to the plane interface. These results may have broad applications in sensing and radiative cooling.     

Scattering by 2D particles deposited on a dielectric planar waveguide: a near-field and far-field study

Scattering of a plane wave by 2D particles (i.e. rods) placed on a dielectric planar waveguide is studied by means of a volume integral approach. The visualization of the near-field surrounding one or two rods points out the role of the guided waves in the interaction between the particles. In the far-field, a peak in the retroreflection direction, as well as secondary peaks, are observed. Different mechanisms involving multiple scattering of the guided waves are proposed.