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Direct method for the quantitative analysis of surface contamination on ultra-low background materials from exposure to dust

Journal Article · · Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment
 [1];  [1];  [2];  [1];  [2]
  1. BATTELLE (PACIFIC NW LAB)
  2. SNOLAB
+ Show Author Affiliations

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. Fallout rates for primordial radionuclides Th-232 and U-238 are measured in the 10E(-8) to 10E(-7) microBq/ day/cm^2 range in a class 10,000 cleanroom at PNNL. Rates range from 10E(-8) microBq/day/ cm^2 to 10E(-5) microBq/day/cm^2 in locations of the class 2,000 SNOLAB cleanroom facility. Accumulation rates for Th-232 and U-238 in non-clean room environments are measured between 10E(-5) and 10E(-4) microBq/day/ cm^2. Accumulation rates for K-40 are of the order of 10E(-5) microBq/day/ cm^2 in the class 1,000 cleanroom at PNNL and it ranges from 10E(-5) to 10E(-3) microBq/day/cm^2 in cleanroom spaces; it is measured at 10E(-3) microBq/day/ cm^2 in non-cleanroom locations at the SNOLAB facility. Accumulation rates for stable Pb, only measured at the SNOLAB facility, range from 10E(-6) to 10E(-3) ng/day/cm^2 in cleanroom spaces. Rates in the two non-cleanroom locations are of the order of 10E(-4) to 10E(-3) ng/day/cm^2. Deposition rates in terms of radioactivity for Pb-210 are inferred from measured stable Pb accumulation rates, assuming a specific activity of 200 Bq/kg for modern refined lead. Accumulation rates of 10E(-10) to 10E(-7) microBq/day/cm^2 in cleanroom spaces and in the 10E(-8) to 10E(-7) microBq/day/cm^2 range in non-cleanroom locations result. A comparison between data obtained from direct ICP-MS measurements and those estimated from current model-based predictors is also performed. Discrepancies of one order of magnitude or higher are observed between estimated and directly measured accumulation rates.

Research Organization:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Organization:
USDOE
DOE Contract Number:
AC05-76RL01830
OSTI ID:
1767155
Report Number(s):
PNNL-SA-153509
Journal Information:
Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 994
Country of Publication:
United States
Language:
English

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