  In this work we present a method for the direct determination of contaminant
fallout rates on material surfaces from exposure to dust. Naturally occurring
radionuclides K-40, Th-232, U-238 and stable Pb were investigated. Until now,
background contributions from dust particulate have largely been estimated from
fallout models and assumed dust composition. Our method utilizes a variety of
low background collection media for exposure in locations of interest, followed
by surface leaching and leachate analysis using inductively coupled plasma mass
spectrometry (ICP-MS). The method was validated and applied in selected
locations at Pacific Northwest National Laboratory (PNNL) and the SNOLAB
underground facility.
