Anthropogenic 236U at Rocky Flats, Ashtabula river harbor, and Mersey estuary: three case studies by sector inductively coupled plasma mass spectrometry.
236U (t(1/2)=2.3 x 10(7) y) is formed as a result of thermal neutron capture by (235)U. In naturally occurring U ores, where a high neutron flux is present from spontaneous fission of (238)U, (236)U/(238)U atom ratios are approximately 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 (236)U/(238)U atom ratios approaching 10(4) ppm. As a result, the presence of very small quantities of reactor-irradiated U will significantly enhance the "background" (236)U/(238)U atom ratio. When sufficiently elevated (236)U/(238)U ratios are present, the determination of (236)U/(238)U by rapid inductively coupled plasma mass spectrometric (ICPMS) methods is attractive. We have used sector ICPMS at medium resolving power (R=3440) to measure (236)U/(238)U atom ratios with a determination limit of 0.2 ppm. The limiting factors in the measurement are the (235)U(1)H(+) isobar and background signal at m/z 236 arising from the (238)U(+) peak tail. Based upon the analysis of replicates and considerations of possible systematic errors, uncertainties of +/-5% are found for (236)U/(238)U atom ratios of 1-100 ppm. This procedure has been demonstrated in studies of anthropogenic (236)U 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 (236)U/(238)U are identified and characterized. Maximum (236)U/(238)U atom ratios observed in RFETS-vicinity soils, the Ashtabula River, and the Mersey Estuary are 2.8, 140, and 4.4 ppm, respectively.
Ketterer
M E
ME
Department of Chemistry, Northern Arizona University, Box 5698, Flagstaff, AZ 86011-5698, USA. Michael.Ketterer@nau.edu
Hafer
K M
KM
Link
C L
CL
Royden
C S
CS
Hartsock
W J
WJ
D003120:Colorado; D004784:Environmental Monitoring; D019015:Geologic Sediments / Q000737:chemistry; D055593:Geological Phenomena; D005844:Geology; D013058:Mass Spectrometry; D009688:Nuclear Reactors; D009820:Ohio; D011005:Plutonium / Q000032:analysis*; D014501:Uranium / Q000032:analysis* / Q000737:chemistry; D014875:Water Pollutants, Radioactive / Q000032:analysis*
D014875:Water Pollutants, Radioactive; D014501:Uranium; D011005:Plutonium