Conférences et séminaires » Séminaire présenté par le Dr. Michael JENTSCHEL, ILL Grenoble
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Par : Dr. Michael JENTSCHEL, ILL Grenoble
Date : vendredi 17 février 2012 à 11h00
Lieu : IPHC, Salle de Réunion 2e étage du Bâtiment 27
The PN3 facility at the neutron high-flux reactor of the Institut Laue-Langevin consist of an tangential through going beam tube equipped with an in-pile sample changer allowing to irradiate samples at a thermal neutron flux of 5 × 1014 neutrons per second and cm2. At the two exits of the beam tube the facility is equipped with crystal spectrometers aiming to carry out ultra high resolution gamma ray spectroscopy. In a first part of the talk an overview on the functioning and specific properties of the instruments will be given. Using a few exemplary experiments the unique performances of these spectrometers are highlighted. The second and main part of the talk focuses on studies to develop gamma ray optics. These concepts, basing on refractive or diffractive scattering should allow to shape gamma ray beams in terms of beam divergence, spot size and monochromaticity. This might be particular important in combination with future highly brilliant gamma ray sources and might push the sensibility of planned experiments by several orders of magnitude. Using diffraction we will demonstrate the experimental feasibility of gamma ray monochromatisation on a ppm level and the creation of a gamma ray beam with nanoradian divergence. Since the refractive index is believed to vanish to zero with 1/E2 the concept of refractive optics has never been considered for gamma rays. The combination of refractive optics with monochromator crystals is proposed to be a promising design. Using our crystal spectrometers we have measured for the first time the refractive index at energies in the energy range of 180 - 2000 keV. The results indicate a deviation from simple 1/E2 extrapolation of X-ray results towards higher energies. A first interpretation of these new results will be presented. We will discuss the consequences of these results on the construction of refractive optics such as lenses or refracting prisms for gamma rays and their combination with single crystal monochromators.
Personne à contacter : Radomira LOZEVA