THE NEW ROSSENDORF NUCLEAR MICROPROBE

Recently a 3 MV tandetron accelerator was put into operation at the Research Center Rossendorf. At this accelerator we have installed a new nuclear microprobe. The object forming aperture can be changed continuously from 0 to 150 mu m and in each direction independently. The magnetic quadrupole triplet delivered by Danfysik has an energy mass product of 45 MeV amu. Magnetic coils placed behind it scan the beam over an area up to 1 x 1 mm(2). A manipulator with X-Y-Z-translation, 360 degrees rotation, and tilt enables us together with the adequate detectors to apply ERDA, PIXE, RES, and NRA. A PC based CAMAC system acquires data from four ADCs. Up to four elemental maps with up to 128 x 128 pixels can be displayed on-line. All events are stored together with their coordinates in list mode for further analysis. A general problem for a quantitative analysis is the accuracy of charge measurement. Using the whole target chamber as a Faraday cup which would be the best method is impossible in our installation. A negatively biased electrode in front of the target for suppressing the secondary electrons cannot be used either. Therefore a precise current integrator was developed which can operate with a positive offset voltage of several hundred volts at the input. The principle of this integrator will be described as well as first experiences and comparisons to other charge measuring methods. Furthermore, a beam monitoring system based on this integrator was set up for an easy control of the beam.