Alpha contamination assessment for D&D activities: Monitoring concrete surfaces

The process of decontaminating and decomissioning former nuclear facilities sometimes requires that large areas of concrete and other materials be scanned to verify they are not contaminated. A specially developed concrete surface monitor (CSM) can greatly expedite that process. The CSM is basically an aluminum box, open on the bottom, that uses an electrostatic field to transport ions created by alpha particles interacting with ambient air to a collection grid or plate. A sensitive electrometer measures the resulting current, which is essentially proportional to surface alpha activity. The initial prototype CSM surveys a surface area of some 300 cm{sup 2} at one time, while a second-generation prototype surveys 2500 cm{sup 2} and is designed to compensate automatically for radon, which can cause substantial errors in estimating surface contamination in some cases. These monitors have been successfully demonstrated on a number of concrete surfaces in situ as well as on concrete pieces cut from former facilities