The presence of radioactive elements, such as U, even at trace levels can make it impractical or impossible to use some materials in semiconductor applications because of randomly induced logic-errors from the decay of the radioactive element. Efforts have been put forth to determine the trace concentration of uranium in a HfO film deposited on Si. This measurement is complicated by the fact that high mass resolution is needed to resolve @super 178@HfSiO@sub 2@ from @super 238@U. In addition, high sensitivity is required in order to measure trace quantities of uranium in the film. The ims-1270 at the National Institute of Standards and Technology has been used for this purpose. Large magnetic sector SIMS instruments are not generally used by the semiconductor SIMS community because of their size and cost. However, they can address some very specific problems that cannot be addressed by smaller instruments that do not have the mass resolution or the transmission. A mass resolution of ~5000 is easily achieved with the ims-1270, while maintaining nearly full transmission. This condition can be used to separate the interference at U. An apparent concentration of U between ~1-10 ppm was measured is the available films. The measurement method, the data and attempted quantification of the measured concentration will be discussed.