Determination of the calibration curve for an ST5 box containing baled waste

摘要

The Trash Monitor Station (TMS), a nondestructive examination facility at the Oak Ridge Y-12 Plant, utilizes gamma scintillation detectors for the isotopic characterization of possible radioactive contamination and measurement of the quantity of potential depleted uranium contamination present in solid waste. Experimental data has been collected and analyzed for construction of a calibration curve for an ST5 box containing baled waste. The raw data consists of gross counts per second derived from five minute counts from three TMS sodium iodide detectors when known amounts of depleted uranium have been placed in a predetermined ''worst case'' location. Extensive analysis of the data indicates that a function of the form y = a + bx + cx(sup (1/2)), where x and y represent sources and net counts per minute respectively, provides the best characterization of a calibration curve. While this equation provides the best prediction, an established method for calculating the minimum detectable amount (MDA) for this type of equation has notbeen found. Therefore, a piece-wise fit of two lines may be preferable at this time. This study provides two linear and two nonlinear models, any one of which may be appropriate for use as the calibration equation for an ST5 box containing baled waste. Two equations for both the linear and nonlinear model types have been supplied to provide a choice between using cpm from a third sodium iodide detector as background or using cpm from a different region of interest as background.