Anthropogenic 236U at Rocky Flats, Ashtabula river harbor, and Mersey estuary: Three case studies by sector inductively coupled plasma mass spectrometry

Michael E Ketterer, K. M. Hafer, C. L. Link, C. S. Royden, W. J. Hartsock

Research output: Contribution to journalArticle

37 Scopus citations

Abstract

236U (t1/2=2.3×107 y) is formed as a result of thermal neutron capture by 235U. In naturally occurring U ores, where a high neutron flux is present from spontaneous fission of 238U, 236U/238U atom ratios are ∼10-4 ppm. In the natural Earth's crust, unaffected by nuclear fallout, these ratios are expected to be on the order of 10-8 ppm. Reactor-irradiated U, however, exhibits high 236U/238U atom ratios approaching 104 ppm. As a result, the presence of very small quantities of reactor-irradiated U will significantly enhance the 'background' 236U/238U atom ratio. When sufficiently elevated 236U/238U ratios are present, the determination of 236U/238U by rapid inductively coupled plasma mass spectrometric (ICPMS) methods is attractive. We have used sector ICPMS at medium resolving power (R=3440) to measure 236U/238U atom ratios with a determination limit of 0.2 ppm. The limiting factors in the measurement are the 235U1H+ isobar and background signal at m/z 236 arising from the 238U+ peak tail. Based upon the analysis of replicates and considerations of possible systematic errors, uncertainties of ±5% are found for 236U/238U atom ratios of 1-100 ppm. This procedure has been demonstrated in studies of anthropogenic 236U in the environment at three locations: (a) offsite soils from the vicinity of the Rocky Flats Environmental Technology site (Golden, Colorado, USA); (b) sediments from the Ashtabula River (Ohio, USA); and (c) sediments from the Mersey estuary (Liverpool, UK). In each of these three locations, definite plumes of elevated 236U/238U are identified and characterized. Maximum 236U/238U atom ratios observed in RFETS-vicinity soils, the Ashtabula River, and the Mersey Estuary are 2.8, 140, and 4.4 ppm, respectively.

Original languageEnglish (US)
Pages (from-to)191-206
Number of pages16
JournalJournal of Environmental Radioactivity
Volume67
Issue number3
DOIs
StatePublished - 2003

    Fingerprint

Keywords

  • U
  • Ashtabula
  • Contamination
  • Inductively coupled plasma mass spectrometry
  • Mersey estuary
  • Plutonium
  • Rocky flats
  • Sediments
  • Uranium

ASJC Scopus subject areas

  • Environmental Science(all)

Cite this