Metrology of the STIP-I Irradiation Fluences Using Activation Foils

The first SINQ Target Irradiation Program, STIP-I, was carried out at the Spallation Neutron Source (SINQ) at the Paul Scherrer Institute (PSI) from July 1998 to December 1999. The purpose was to assess the effects on materials of high-energy protons and spallation neutrons. To this end, a number of samples and specimen types were included within the SINQ target structure. In addition to the samples, numerous activation foils were included at various locations to characterize the fluence and spectra. The foil materials used were Al, Au, Co, Cu, Fe, Nb, Ni and Ti. The target received a total charge of 6.8 A-h and reached a peak fluence of 3.2x1025 p/m2. Post-irradiation assessment of these foils was complicated by the large number of thermal neutrons from the moderated SINQ target. Some reactions, notably Al→Na22, were influenced by large n, gamma cross sections of the activated species. Overall, the results confirmed the physics calculations of the proton and neutron fluences. In addition, exposure estimates of the dpa, He, and H generation were made for the various materials. Based on the estimated fluences, the maximum damage reached in stainless-steel materials was around 14 dpa with approximately 800 appm of He and ∼6500 appm of H generated. (authors)