${}^{210}$Pb measurements at the André E. Lalonde AMS Laboratory for the radioassay of materials used in rare event search detectors

Abstract

Naturally occurring radionuclide ${}^{210}$Pb ($T_{1/2}$=22.2 y) is an important source of background in rare event searches, such as neutrinoless double-$\beta$ decay and dark matter direct detection experiments. When a sample mass of hundreds of grams is available, $\gamma$-counting measurements can be performed. However, there are other cases where only grams of sample can be used. For these cases, better sensitivities are required. In this paper, in collaboration with the Astroparticle Physics group at Carleton University, the capabilities of the A.E. Lalonde AMS Laboratory at the University of Ottawa for ${}^{210}$Pb measurements are discussed. PbF${}_2$ and PbO targets were used, selecting in the low energy sector, respectively, (PbF${}_3$)${}^{-}$ or (PbO${}_2$)${}^{-}$ ions. For fluoride targets, the blank ${}^{210}$Pb/${}^{206}$Pb ratio was in the 10${}^{-14}$ to 10${}^{-13}$ range, but current output was lower and less stable. For oxide targets, current output showed better stability, despite a significant difference in current output for commercial PbO and processed samples, and background studies suggested a background not much higher than that of the fluoride targets. Both target materials showed, therefore, good performance for ${}^{210}$Pb AMS assay. Measurements of Kapton films, an ultra-thin polymer material, where masses available are typically just several grams, were performed. 90% C.L. upper limits for the ${}^{210}$Pb specific activity in the range of 0.74-2.8 Bq/kg were established for several Kapton HN films.

arXiv comment16 pages, 2 figures, 7 tables. We have noticed on a mistake in version 1: due to a typo in the spreadsheet used to analyze the data, where we forgot to use the charge state of 206Pb3+ to calculate the 210Pb/206Pb ratio, the uncorrected ratios are 3 times lower. Since this affects also the standards, the final corrected 210Pb/206Pb ratio are not very different from those presented in version 1

References in corpus (15)

• A Unified Approach to the Classical Statistical Analysis of Small Signals
• Dark Matter Search Results from the Complete Exposure of the PICO-60 C${}_3$F${}_8$ Bubble Chamber
• Search for Neutrinoless Double-Beta Decay with the Complete EXO-200 Dataset
• Sensitivity and discovery potential of the proposed nEXO experiment to neutrinoless double beta decay
• First results from the NEWS-G direct dark matter search experiment at the LSM
• A Search for Neutrinoless Double-Beta Decay in ${}^{76}$Ge with 26 kg-yr of Exposure from the MAJORANA DEMONSTRATOR
• The Majorana Demonstrator Radioassay Program
• Design and Construction of the DEAP-3600 Dark Matter Detector
• nEXO Pre-Conceptual Design Report
• Radiogenic Neutron Yield Calculations for Low-Background Experiments
• Trace radioactive impurities in final construction materials for EXO-200
• Assay methods for U-238, Th-232, and Pb-210 in lead and calibration of Bi-210 bremsstrahlung emission from lead
• Ultra-low radioactivity Kapton and copper-Kapton laminates
• Radon Daughter Plate-out Measurements at SNOLAB for Polyethylene and Copper
• Backgrounds in the DEAP-3600 Dark Matter Experiment