Identification and quantification of 233U at a legacy waste site
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Date
2012-10-16
Journal Title
Journal ISSN
Volume Title
Publisher
Australian Nuclear Science and Technology Organisation
Abstract
The Little Forest Burial Ground (LFBG), located within the Australian Nuclear Science and Technology Organisation (ANSTO) buffer zone, was used to dispose of low level radioactive waste in shallow trenches during the 1960s. Operational records suggest that natural and anthropogenic radionuclides were disposed of,
including uranium-233 (233U), a fissile isotope of uranium. This paper outlines how 233U was identified and then quantified in environmental samples from LFBG in the presence of other uranium isotopes. Alpha spectrometry sources were prepared using 232U as a tracer and counted to give a qualitative indication of 233U from the combined 233+234U activity. The primary region of interest (ROI) of 233U is a doublet peak, with emission energies of 4.784 MeV (13%) and 4.824 MeV (84%). This peak, if present in an alpha spectrum, will overlap with the primary ROI of 234U, also a doublet of 4.722 MeV (28%) and 4.775 MeV (71%). Based on alpha spectrometry results, samples thought to contain 233U were then prepared for Accelerator Mass Spectrometry (AMS). AMS was used to measure the 234U/233U isotope ratio. The isotope dilution method, with 236U spike, was not able to be used with samples from this study site as low levels of this anthropogenic
isotope have also been detected. Instead, the isotope ratio 234U/233U from AMS was used with the combined 233+234U activity from alpha spectrometry to derive the 233U activity. This combination of techniques enables 233U to be quantified in these types of environmental samples.
Description
Keywords
Uranium 233, ANSTO, New South Wales, Australia, Radioactive wastes, Ground disposal, Tracer techniques, Spectroscopy
Citation
Harrison, J. J., Child, D. P., Hotchkis, M. A. C., Payne, T. E., Thiruvoth, S., & Wilsher, K. L. (2012). Identification and quantification of 233U at a legacy waste site. Paper presented to the 12th South Pacific Environmental Radioactivity Association Conference (SPERA 2012), Sydney, Australia, Tuesday 16 October – Friday 19 October 2012. Lucas Heights, NSW: Australian Nuclear Science and Technology Organisation. (pp. 55).