Simulation experiments for the sputtering of niobium by 14 MeV neutrons

Simulation experiments for the sputtering of niobium by 14 MeV neutrons are conducted at the Berlin Cyclotron with protons of 11 to 20 MeV which pass through a sandwich of niobium target foils and silicon catcher disks. The stack is assembled in an UHV chamber and is irradiated to doses of 0.7 to 1.4 × 10¹⁸ p/cm². The sputtered material is detected by RBS, taking advantage of Si background reduction by the 〈111〉 channeling effect and by electronic pile-up rejection. The measured sputter ratios are in the forward direction (1.0–2.4) × 10^?4 for the first irradiation and (1.0–2.5) × 10^?5 for a second (subsequent) irradiation; in the backward direction sputter ratios are found to be considerably lower, between several 10^?6 (limit of detection) and 2.8 × 10^?5 (maximum). The emission of radioactive recoils is also observed through 7 spectrometry of targets and collectors.