title: Minimum detectable concentration as a function of gamma walkover survey technique.
abstract: Gamma walkover surveys are often performed by swinging the radiation detector (e.g., a 2-inch by 2-inch sodium iodide) in a serpentine pattern at a near constant height above the ground surface. The objective is to survey an approximate 1-m swath with 100% coverage producing an equal probability of detecting contamination at any point along the swing. In reality, however, the detector height will vary slightly along the swing path, and in some cases the detector may follow a pendulum-like motion significantly reducing the detector response and increasing the minimum detectable concentration. This paper quantifies relative detector responses for fixed and variable height swing patterns and demonstrates negative impacts on the minimum detectable concentration. Minimum detectable concentrations are calculated for multiple contaminated surface areas (0.1, 1.0, 3, 10, and 30 m2), multiple contaminants (60Co, 137Cs, 241Am, and 226Ra), and two minimum heights (5 and 10 cm). Exposure rate estimates used in minimum detectable concentration calculations are produced using MicroShield™ v.7.02 (Grove Software, Inc., 4925 Boonsboro Road #257, Lynchberg, VA 24503) and MDCs are calculated as outlined in NUREG-1575. Results confirm a pendulum-like detector motion can significantly increase MDCs relative to a low flat trajectory, especially for small areas of elevated activity--up to a 47% difference is observed under worst-modeled conditions.
authors.affiliation: Oak Ridge Associated Universities, Independent Environmental Assessment and Verification, 1299 Bethel Valley Road, Oak Ridge, TN, USA. king.david@orau.org
authors.forename: David A
authors.initials: DA
authors.lastname: King
authors.forename: Nickolas
authors.initials: N
authors.lastname: Altic
authors.forename: Colt
authors.initials: C
authors.lastname: Greer
mesh_terms: D004781:Environmental Exposure / Q000032:analysis / Q000706:statistics & numerical data; D004784:Environmental Monitoring / Q000379:methods* / Q000706:statistics & numerical data; D005720:Gamma Rays; D006283:Health Physics; D006801:Humans; D012990:Soil Pollutants, Radioactive / Q000032:analysis*; D016138:Walking
chemical_list: D012990:Soil Pollutants, Radioactive