Investigating the lead-210 background in lead materials and chemical reagents
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Date
2022-11-29
Journal Title
Journal ISSN
Volume Title
Publisher
South Pacific Environmental Radioactivity Association
Abstract
SABRE (Sodium iodide with Active Background REjection) is a direct detection dark matter
experiment based on ultra-pure NaI(Tl) crystals. This experiment is well-shielded against external
radiation and thus its background rate is driven by radioactive contaminants in the detector
material and in the materials used for the construction of the experimental setup. Such radioactive
contamination may come from long-lived, naturally occurring radionuclides or from cosmogenic
activation. Therefore, a careful selection and development of ultra-pure materials and equipment is
required, as well as a detailed knowledge of the residual radioactivity. Here, we focus on exploring the extraction of the radioisotope lead-210 (210Pb) in analytical grade NaI
prior to examining Astro-grade NaI(Tl), which will eventually serve in the SABRE-South experiment as
a scintillator detector for dark matter studies based in the Southern Hemisphere. We aim to measure
210Pb in NaI by accelerator mass spectrometry (a single atom counting technique), however this is
challenging owing to the anticipated large mass of 1 kg. We will discuss two methods to extract
Pb using different resins such as the Anion Exchange Resin (1-X8, 100-200 mesh Chloride form) and
Sr® resin (100-150 mm).
Furthermore, it is essential that any material and reagents in use should contain as little 210Pb as
possible. For the chemical extraction of 210Pb from NaI, a stable Pb carrier is being used, which may
contain traces of 210Pb as well. As 210Pb has a half-life of 22.2 years, the “older” the material (i.e., age of
manufacturing and processing) the better, as most, if not all, of the 210Pb has decayed. However, 210Pb
is a decay product of U, which is omnipresent in the environment. Therefore, if uranium has not been
completely removed from the Pb material during processing, 210Pb will be continuously produced.
Here, we will present results for a series of Pb materials together with various reagents which were
measured using the 1 MV Vega accelerator at ANSTO. Their 210Pb/208Pb isotopic ratios vary between
(3-30)´10-14 for the Pb carriers (0.38-173 mBq 210Pb/g) and range from 1´10-14 to 3´10-11 for the reagents
(4-194 mBq 210Pb/g), respectively.
Description
Keywords
Lead 210, Materials, Chemicals, Reagents, Sodium iodides, Nonluminous matter, Crystals, Contamination, Radioisotopes, Southern Hemisphere, Mass spectroscopy
Citation
Froehlich, M., Hotchkis, M., Dastgiri, F., Fifield, K, Koll, K., Merchel, S., Pavetich, S., Slavkovská, Z., Tims, S., & Wallner, A. (2022). Investigating the lead-210 background in lead materials and chemical reagents. Paper presented to SPERA 2022 - Connecting People, developing solutions for a Changing Environment, 28-30 November 2022, Chrischurch, New Zealand. (pp. 31-32). Retrieved from: https://au-admin.eventscloud.com/file_uploads/baa6bb17538b457fbd436f1552075bea_SPERA2022e-handbook.pdf