ABSOLUTE CALIBRATION OF THE O-16 (ALPHA,ALPHA) O-16 ELASTIC-SCATTERING RESONANCE AT 7.30-7.65 MEV AND APPLICATIONS TO OXYGEN DEPTH PROFILING

The differential cross-section of the O-16(alpha, alpha)O-16 elastic s cattering resonance at 7.30-7.65 MeV has been calibrated with an overa ll accuracy of 4% at 170-degrees scattering angle (laboratory frame of reference) using anodized Ta2O5 films of pre-calibrated thickness as standards. This extremely strong (about 170 times the Rutherford cross -section) and broad (about 300 keV wide) resonance varies slowly with energy in the range 7.34-7.64 MeV, has a maximum value of 837 mb/sr at 7.61 MeV, and falls off abruptly above 7.64 MeV and below 7.34 MeV. T he angular dependence of the resonance was measured in the range 140-1 72-degrees at incident energy 7.62 MeV and was found to increase monot onically toward 180-degrees. This strong resonance allowed us to measu re the oxygen content in the very heavy element target ThO2 pellets an d in oxidized InP substrates with detection sensitivity in the atomic monolayer range. The large width of this resonance allowed oxygen dept h profiling to several microns with depth resolution a few tens of nm. Measurements combined with RUMP computer simulations using TRIM stopp ing cross-sections and our measured values of the elastic resonance sc attering cross-section have been used to depth profile SiO2 surface an d buried layers in SIMOX structures.