LARGE THETA(C) NEUTRON SUPERMIRRORS AND STRESS EVOLUTION WITH IRRADIATION

Supermirror neutron guides presenting an apparent critical edge (theta (c)) twice as large as natural nickel are now commonly used, We presen t results obtained on coatings with an apparent critical edge three ti mes as large as natural nickel and deposited on glass plates of large area. In neutron guides, in order to avoid any initial loss of neutron s, one would be interested in using these high theta(c) supermirrors i n the early parts of the guides. At this place, they are submitted to a very strong irradiation. The stability of the coating in these condi tions is not established yet, We have undertaken the study of strong i rradiation effects on these multilayers. We present results on three d ifferent points: (1) the evolution of the reflectivity, (2) the evolut ion of the crystalline structure, (3) the evolution of the internal st resses in the layers.