An In-Situ, Long-Term Underground Monitor for Radioactive Contamination

James Durham
Department of Environmental and Radiological Health Sciences
Colorado State University

This presentation will discuss the current status of a DOE-funded project to develop a simple and inexpensive portable radiation sensor system for use in long-term monitoring of the soil around remediated waste sites.  The system uses the Pulsed Optically Stimulated Luminescence technique to remotely interrogate an aluminum oxide (-Al2O3:C) radiation sensor via an optical fiber. The system consists of a small aluminum oxide fiber attached to a long fiber optic channel and a portable reader consisting of a visible laser and a photomultiplier tube.  The sensors and are easy to install and operate and should require little to no maintenance.  A single reader can be used to interrogate multiple individual sensors or the sensors could be multiplexed for automated readout of multiple sensors.  The current minimum detectable dose for the system is on the order of 5 Gy, which will allow monitoring of potential radioactive plumes around remediated radioactive waste sites at a frequency that exceeds that of soil sampling.  The current capabilities of the system can measure soil concentrations of 50 pCi/cm3 in as little as 150 hours for 137Cs and 200 h for 90Y.  Potential developments that could decrease the minimum detectable dose to lower levels will also be discussed.  Additional applications, including real-time measurements of high dose rates, will be described.