Rapid Gamma Spectroscopic Analyses of TRU/LLW Soil Cores

INTRODUCTION

High-resolution field gamma spectroscopy was used to provide rapid analyses of radiological constituents in soil cores taken from the vicinity of Corehole 8 Tank W-1A at ORNL. The purpose of this characterization project was to generate three-dimensional maps of the extent of TRU and LLW contamination in soil around the tank. Geoprobe dual-tube soil sampling was used to collect 1.15-in diameter soil cores up to 36-in long. These cores were immediately brought to two adjacent ISOCS gamma spectroscopy stations for measurements. Typically, a 12-in long core segment was measured for 15 minutes, and the results were reported within 30 minutes. Fast turnaround times were necessary to support the dynamic sampling plan. The primary detected radioactive contaminants were 241Am, 137Cs, 152Eu, 154Eu, and daughters of 232U, 233U, and 232Th. The quantification of 241Am in the presence of high concentrations of 137Cs presented some special challenges. Using customized counting geometries, lead shielding, and collimators, it was possible to quantify 46 nCi/g of 241Am in the presence of 21,000 nCi/g of 137Cs. Detection limits for 241Am were typically less than 10 nCi/g. The results of ~300 measurements performed at 64 probe locations will be presented.