Irradiation ageing of alkali-borosilicate neutron guides : macroscopic and vitreous structure study

Orateur : Romain BOFFY (Institut Laue-Langevin)

Alkali borosilicate glasses are widely used as substrate materials for manufacturing neutron mirrors and guides. Their interest, compared to purely Silica-based glasses, lies in their boron oxide content. It provides an efficient shielding for the environment thanks to the (n,a) Boron capture reactions of the particles transmitted across the neutron reflecting layers. The relevance of the presented study stems from the splintering and implosion of neutron beam lines due to over-irradiation registered at several neutron scientific facilities worldwide. To tackle this issue, the Institut Laue-Langevin (Grenoble, France) and the European Spallation Source (Lund, Sweden) have launched an investigation onto the mechanisms linking the neutron exposition to the glass failure. The guide damage has been attributed to He and Li ions resulting from (n,a) reactions with energies of 1470 keV and 840 keV respectively. Due to their high energy compared to the inter-atomic binding ones, these ions induce a ballistic mixing in the glass network. The aim of this study was then to relate the glass network modifications with changes occurring on its macroscopic shape. The study consisted in monitoring the glass properties as a function of the neutron dose received by means of the concurrent use of different experimental techniques such as : SANS, NMR, RAMAN etc.

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