Reprocessing of B-10-contaminated Be-10 AMS targets.

• Main Authors: Simon, KJ, Pedro, JB, Smith, AM, Child, DP, Fink, D
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2013
• Subjects: REPROCESSING; CONTAMINATION; BERYLLIUM; BORON; mass spectrometry; ICE; Antarctic; Antarc*; ice core
• Online Access: http://apo.ansto.gov.au/dspace/handle/10238/4597

Be-10 accelerator mass spectrometry (AMS) is an increasingly important tool in studies ranging from exposure age dating and palaeo-geomagnetism to the impact of solar variability on the Earth's climate. High levels of boron in BeO AMS targets can adversely impact the quality of Be-10 measurements through interference from the isobar B-10. Numerous methods in chemical sample preparation and AMS measurement have been employed in order to reduce the impact of excessive boron rates. We present details of a method developed to chemically reprocess a set of forty boron-contaminated BeO targets derived from modern Antarctic ice. Previously, the excessive boron levels in these samples, as measured in an argon-filled absorber cell preceding the ionisation detector, had precluded routine AMS measurement. The procedure involved removing the BeO + Nb mixture from the target holders and dissolving the BeO in hot concentrated H2SO4. The solution was then heated with HF to remove the boron as volatile BF3 before re-precipitating as Be(OH)(2) and calcining to BeO. This was again mixed with niobium and pressed into fresh target holders. Following reprocessing, the samples gave boron rates reduced by 10-100x, which were sufficiently low and similar to previous successful batches of ice core, snow and associated blank samples, thus allowing a successful Be-10 measurement in the absence of any boron correction. Overall recovery of the BeO for this process averaged 40%. Extensive testing of relevant processing equipment and reagents failed to determine the source of the boron. As a precautionary measure, a similar H2SO4 + HF step has been subsequently added to the standard ice processing method. © 2013, Elsevier Ltd.