Evaluation and mitigation of trace 210Pb contamination on copper surfaces

Abstract

Clean materials are required to construct and operate many low-background physics experiments. High-purity copper has found broad use because of its physical properties and availability. In this paper, we describe methods to assay and mitigate 210Pb contamination on copper surfaces, such as from exposure to environmental radon or coming from bulk impurities. We evaluated the efficacy of wet etching on commercial samples and observed that 210Po contamination from the copper bulk does not readily pass into solution. During the etch, the polonium appears to trap at the copper–etchant boundary, such that it is effectively concentrated at the copper surface. We observed a different behavior for 210Pb; high-sensitivity measurements of the alpha emissivity versus time indicate the lowest level of 210Pb contamination ever reported for a commercial copper surface: 0±12nBq/cm2 (1σ). Additionally, we have demonstrated the effectiveness of mitigating trace 210Pb and 210Po surface backgrounds using custom, high-purity electroplating techniques. These approaches were evaluated utilizing assays performed with an XIA UltraLo-1800 alpha spectrometer.