Reprocessing of 10B-contaminated 10Be AMS targets

• Main Authors: Simon, KJ, Pedro, JB, Smith, AM, Child, DP, Fink, D
• Format: Conference Object
• Language: English
• Published: 12th International Conference on Accelerator Mass Spectrometry (AMS-12) 2011
• Subjects: ANTARES Facility; Beryllium 10 Tagaret; Reprocessing; Antarctica; Argon; Berkelium; Antarctic; Recess; Antarc*
• Online Access: http://apo.ansto.gov.au/dspace/handle/10238/3628; http://www.gns.cri.nz/ams12/

Forty 10Be samples of Antarctic ice (DSS0506-pit) along with associated procedural blanks, measured at the ANTARES AMS facility at ANSTO were found to have 10-100 times the 10B levels of routine BeO samples and blanks (full procedural blanks with this beryl carrier are typically 10Be/9Be <5 x 10-15). These exceptionally high boron rates (measured via an active absorber cell filled with argon gas), coupled with the relatively low 10Be/9Be ratios of ice samples, made any correction to the raw 10Be detector count rate highly unreliable and uncertain. As this was a unique sample set, a method for reprocessing the targets to remove the boron was developed and tested. For measurement on ANTARES ~0.5mg BeO is mixed with ~2.0mg of niobium powder and rearpressed into an aluminium target holder with a 1.6mm diameter recess at 120 kPa. To reprocess the samples, this BeO/Nb mixture was physically removed from the target holders by pushing the sample loading pin forward with a hand press. The beryllium was separated from the niobium by dissolving the BeO in concentrated H2SO4. This solution was then heated with HF to remove the boron as BF3. The beryllium was then re-precipitated as Be(OH)2 and calcined to BeO, which was then mixed with new niobium powder before being rear-pressed into a detachable cap target holder with a smaller (1 mm) diameter recess. Overall yields for this process averaged 40%. Boron levels for all the original samples and blanks returned to acceptable levels, with 10Be/9Be blanks of ~10 x 10-15. Extensive testing of the equipment, reagents and laboratory 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, resulting in consistently low boron levels without any decrease in processing yields.Copyright (c) 2011 AMS12