Element-dependent ERDA probing depths using different detection systems

Elastic Recoil Detection Analysis (ERDA) of a pyrex-glass sample is carried out in the elemental range of Z=5-20 using element dispersive ionization chambers and a time-of-flight (TOF-E) system, respectively. It is shown that recoil identification with the gas detectors is limited to energies significantly higher than the values assigned to the maximum electronic stopping power of the different species in the detector gas. As a consequence, the in-target depth accessible for analysis decreases rapidly with increasing atomic number of the recoils in the case of the comparatively small projectile energies available from a 5 MV tandem accelerator. Mass discrimination using TOF spectrometry is effective down to significantly smaller energies, giving larger probing depths with unchanged beam and geometry parameters. This advantage over the gas detectors is most prominent with the heaviest recoils analyzed. Based on the multielement spectra obtained with 35 MeV Cl-35 and 210 MeV I-127 analyzing beams, respectively, an extrapolation onto a 2 MV tandem machine providing 12 MeV Cl-35 ions shows that element-discriminating analysis is possible also with small accelerators if TOF systems are employed for recoil detection. (C) 1997 Elsevier Science B.V.