Neutron and X-ray experiments at high temperature
2014 Advanced technologies, like for instance aerospace or nuclear engineering require the most exhaustive information on the behaviour of materials used at very high temperature such as ceramics, refractory alloys or molten metals. Among high temperature techniques, X-rays and more recently neutron scattering have appeared as powerful tools to get information, mainly structural, on these materials in their working conditions. High temperature devices (above 2 000 K) developed for that purpose, based on various heating techniques (induction, imaging furnaces, lasers, gas-flame heaters and principally Joule heated devices) are reviewed. Some crucial points are particularly emphasized such as : 2014 the determination of the real temperature (thermocouples and optical pyrometry) in the scattering zone hardly accessible partly due to the unavoidable thermal gradients, 2014 the chemical reactivity of the sample with its surrounding, i.e. atmosphere and sample holder. Neutrons, mainly because of their low absorption by matter, allow the work on real bulky materials and give a greater freedom in the conception of high temperature scattering devices compared to X-rays. At the present time thermal neutron high flux reactors offering a wide range of neutron wavelengths are available, and a new generation of more and more efficient multidetectors has emerged in the last decade; the data acquisition and consequently the high temperature exposure time have been notably reduced, opening a way for precise and reliable experiments in the 3 000 K range. This very high temperature domain already studied by a few other techniques can also be investigated by neutron scattering. Revue Phys. Appl. 19 (1984) 649-662 SEPTEMBRE 1984, PAGE (*) The author’s personal work has been done at the ILL (HFR Grenoble). Now with the Equipe de Physico-Chimie Moleculaire, CENG-DRF, 85X, 38041 Grenoble Cedex, France. REVUE DE PHYSIQUE APPLIQUEE. T. I9, N° 9, SEPTEMBRE 1984 45 Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/rphysap:01984001909064900
Pulsed Neutron Diffraction in Special Sample Environments
Neutron diffraction is a powerful tool for structural studies of samples in special sample environments because of the high penetrating power of neutrons compared to X-rays. The neutrons readily penetrate special sample containers, heat shields, pressure vessels, etc., making it unnecessary in most cases to compromise the effectiveness of the sample environment system by providing windows for the incident and scattered neutrons. Pulsed neutrons obtained from an accelerator-based pulsed neutron source offer the additional advantage that many diffraction experiments can be done at a single, fixed scattering angle by the time-of-flight technique. Thus, if windows are needed (e.g., in an especially thick-walled sample vessel such as a pressure cell), they need to cover only a limited angular range. More importantly, in the fixed-angle scattering geometry, shielding and collimation can be optimized in order to access the largest possible sample volume with neutrons while completely avoiding scattering from the surrounding sample vessel. Thus, the data are free from unwanted background scattering which could hamper data interpretation. In this paper, the basic principles of neutron diffraction in special sample environments are discussed and examples of apparatus used for neutron diffraction measurements at low temperature, high temperature, and high pressure are presented. The concepts are illustrated with several unique scientific results taken from the published literature.
Balloon assisted translocation of the mitral anterior leaflet to prevent left ventricular outflow obstruction (BATMAN): A novel technique for patients undergoing transcatheter mitral valve replacement
Transcatheter mitral valve replacement (TMVR) is an option for patients at high risk for mitral valve replacement or repair via sternotomy or left thoracotomy approach. TMVR carries up to 22% risk of left ventricular outflow tract (LVOT) obstruction. Severe LVOT obstruction can have devastating hemodynamic and clinical consequences.