MATHEMATICAL-MODELING OF SECONDARY-ION ENERGY-SPECTRA

An attempt has been made to compose a mathematical model of secondary ion energy spectra, taking into account the sputter process, the ioniz ation process and the transmission of the secondary ion mass spectrome ter. In this model a new equation for the transmission of the instrume nt was formulated. The percentage fit of the model was equal to 99.9+% for 80% of the tested cases and 99+% for all measured energy distribu tions. A total of 59 energy distributions were tested. It was hoped th at the various mathematical parameters used in the expressions to desc ribe the above processes and characteristics will provide a direct lin k with the variation of the measured isotopic ratios and hence a bette r insight into the reasons for this variation. Unfortunately, this obj ective was not achieved since the uncertainty of the calculated ratio by model-fitting the energy distributions is larger than the measured uncertainty. However, the model provides some insight into the energy dependent fractionation observed within individual measurements.