OPTIMIZATION OF MATERIAL AND SHAPE FOR NUCLEAR MICROPROBE APERTURES

In a nuclear microprobe the beam (usually 1-3 MeV protons) is focused on the target to a lateral spot size of micrometer dimensions, using a focusing lens and at least two beam-defining apertures. Apart from ot her affecting parameters, the lateral resolution also depends on the s cattering and energy loss of the projectiles transmitting the region n ear the edge of the aperture, the ''transparency zone'', The depth of this zone is influenced by the shape, material, and surface roughness of the aperture. This influence was investigated quantitatively for 3 MeV protons using both theoretical and experimental studies. The theor etical studies included the multiple scattering theory as well as a ra y-tracing simulation, The experiments were performed using the Bochum nuclear microprobe together with the STIM technique, The results of th e studies showed that W, WC, Pt, and Mo are suitable aperture material s, From ray-tracing simulations it turned out that the effect of apert ure surface roughness on beam quality is strongly dependent on the spe cific material, The cylindrical slit geometry was found to be most pro mising for nuclear microprobe apertures.