ENERGY-LOSS FLUCTUATIONS CAUSED BY RUTHERFORD SCATTERING

An isobutane filled ionisation chamber has been constructed with three anodes to provide atomic number assignments for heavy ions with energies greater than 1 MeV per nucleon. The energy loss section of the ion chamber is divided into two small sections to enable identification of events where abnormal energy loss profiles along the heavy ion track would cause false assignments. In an experiment with Cr-49 ions such abnormal events were clearly identified and are shown to be due to Rutherford scattering of the Cr-49 ions off the carbon nuclei of the isobutane ion chamber gas. The split energy loss section of the ion chamber enables rejection of these events to several orders of magnitude, with the rejection factor depending on the details of the heavy ion speed and type.