Four methods for determining the composition of trace radioactive surface contamination of low-radioactivity metal

Abstract

Four methods for determining the composition of low-level uranium- and thorium-chain surface contamination are presented. One method is the observation of Cherenkov light production in water. In two additional methods a position-sensitive proportional counter surrounding the surface is used to make both a measurement of the energy spectrum of alpha particle emissions and also coincidence measurements to derive the thorium-chain content based on the presence of short-lived isotopes in that decay chain. The fourth method is a radiochemical technique in which the surface is eluted with a weak acid, the eluate is concentrated, added to liquid scintillator and assayed by recording beta-alpha coincidences. These methods were used to characterize two `hotspots' on the outer surface of one of the He-3 proportional counters in the Neutral Current Detection array of the Sudbury Neutrino Observatory experiment. The methods have similar sensitivities, of order tens of ng, to both thorium- and uranium-chain contamination.

22 pages, 19 figures

References in corpus (6)

• Big-Bang nucleosynthesis (Particle Data Group mini-review)
• The Cosmological Parameters 2006
• Direct Evidence for Neutrino Flavor Transformation from Neutral-Current Interactions in the Sudbury Neutrino Observatory
• Independent Measurement of the Total Active 8B Solar Neutrino Flux Using an Array of 3He Proportional Counters at the Sudbury Neutrino Observatory
• A radium assay technique using hydrous titanium oxide adsorbent for the Sudbury Neutrino Observatory
• High sensitivity measurement of 224Ra and 226Ra in water with an improved hydrous titanium oxide technique at the Sudbury Neutrino Observatory

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• Combined Analysis of all Three Phases of Solar Neutrino Data from the Sudbury Neutrino Observatory
• The Sudbury Neutrino Observatory
• Measurement of the ${\nu }_e$ and Total ${}^8$B Solar Neutrino Fluxes with the Sudbury Neutrino Observatory Phase-III Data Set
• Ultra-pure Nickel for Structural Components of Low-Radioactivity Instruments