A spectrometer for low energy heavy ion ERDA

An ERDA detector telescope consisting of a time-of-flight (ToF) system combined with a gas ionization chamber (GIC) has been developed which is specialized for the identification of very low energy ions. Equipped with a large area patterned silicon nitride entrance window of 130 nm thickness, the GIC allows heavy ion detection well below 1 MeV with sufficient resolution for particle identification. The ToF system has a start detector with a diamond-like carbon (DLC) foil of only 0.5 μg/cm2, which warrants excellent energy resolution for depth profiling. The system has been tested with 127I, 197Au and 48Ti projectiles of energies between 1.5 and 12 MeV. In the low mass range (up to 30 amu) the mass resolution is better than 1 in 35 at a recoil energy of approximately 3 MeV. A depth resolution of 1.5 nm (FWHM) has been obtained at a TiO2 surface using 1.5 MeV 127I projectiles. The spectrometer is well suited for high resolution near-surface ERDA analysis even at accelerators with very low beam energies.