SANS investigation of neutron-irradiated pressure vessel steels and model alloys

Application of small angle neutron scattering to RPV steels had to be reconsidered, when it was discovered by Atom Probe investigations that irradiation-induced clusters in RPV steels do contain Fe. It was no longer justified in general to determine the total volume fraction of clusters, as long as the magnetic moment of the Fe atoms inside the clusters is not known for sure. The aim of the talk is to compile ways out from this dilemma. The first part is devoted to selected SANS results obtained assuming non-magnetic clusters. The second part is a compilation of 5 ways to solve the questions that arise, if this assumption is not justified. In the third part it will be analyzed, which conclusions remain valid and which have to be modified. If the magnetic character of scatterers is not known in advance, SANS and 3DAP can be combined synergistically: 3DAP yields cluster composition, but sensitivity to vacancies is low. SANS (A-ratio) is particularly sensitive to the vacancy fraction.