Flett Research - Radioisotope Methods

Cesium-137 (Cs-137) in sediment and soil is determined by counting the gamma emissions at 661.6 KeV that are emitted in 82.5% of the decays. The gamma radiation is relatively strong and therefore penetrates through several centimetres of sediment material with little attenuation.  This procedure is modified from EML HASL-300 Method Ga-01-R.  The method detection limit (MDL) with our HPGe detector is 0.3 DPM/g (95% confidence) for an 80,000 second counting period when measuring 9 g of dry sample. The method detection limit can be decreased to 0.1 DPM/g if 32 g of sample is used.

Lead-210 (Pb-210) in sediment, soil and peat is by measurement of the Po-210 grand daughter which is in secular equilibrium with Pb-210 within 2 years of Pb-210 deposition.  This procedure is modified from Eakins and Morrison (1978). Samples are first spiked with a Po-209 yield tracer, then digested in hot nitric acid. The digest is dried and made up in 0.3 N HCl and then the Po-210 and Po-209 alpha emitting isotopes are plated out on silver planchets followed by alpha spectrometry to determine the activity of the polonium isotopes.  In the case of sediment and soil samples, an initial cleanup of samples may be done by distilling the polonium out of the samples at 500°C prior to nitric acid digestion.  The detection limit (MDL) for 0.25 - 0.5 g (dry wt.) sample is between 0.1 - 0.2 DPM Po-210/g dry sample at a 95% confidence level for 60,000 second counting time.  This can vary slightly and depends upon the amount of sample and the detector and recovery efficiency of each sample. 

Radium-226 (Ra-226) in sediment, soil and peat is determined by radon-222 emanation.  This procedure is modified from that of Mathieu et al. (1988). The method detection limit (MDL) is dependant on the amount of sample analyzed.  For a 60,000 second counting time the MDL @ 95% confidence for 2g of dry samples is 0.1 DPM/g and for 0.5g of dry samples is 0.5 DPM/g.

Methods References:

Environmental Measurements Laboratory, US Department of Energy - HASL-300 Method Ga-01-R Gamma Emitters in the Environment by Energy, HASL EML Procedures Manual, 28th Edition, Februray 1997.

 Eakins, J. D. and R. T. Morrison. 1978. A new procedure for the determination of lead-210 in lake and marine sediments. International Journal of Applied Radiation and Isotopes. 29, 531-536.

Mathieu, G.G., P.E. Biscaye, R.A. Lupton and D.E. Hammond. System for measurement of ²²²Rn at low levels in natural waters. 1988. Health Physics. 55, 989 – 992.

Other References:

Appleby, P.G. and F. Oldfield. 1978. The calculation of Lead-210 dates assuming a constant rate of supply of unsupported Pb-210 to the sediment. Catena. 5, 1-8.

Flynn, W.W. 1968. The determination of low levels of Polonium-210 in environmental materials. Anal. Chim. Acta. 43, 221-227.

Ritchie, J.C. and J. R. McHenry. 1990. Application of radioactive fallout cesium-137 for measuring soil erosion and sediment accumulation rates and patterns: a review. J. Environ. Qual. 19, 215-233.

Carter, M.W. and A.A. Moghissi. 1977. Three decades of nuclear testing. Health Phys. 33(1), 55-71.

Pennington, W., R.S. Cambray and E.M. Fisher. 1973. Observations on lake sediments using fallout Cs-137 as a tracer. Reprint from Nature. 242(5396), 324-326. March 30, 1973.

Durham, R.W. and S.R. Joshi. 1980. The Pb-210 and Cs-137 profiles in sediment cores from Lakes Matagami and Quevillon, northwest Quebec, Canada. CAN. J. Earth Sci. 17, 1746-1750.

Pourchet, M. and J.F. Pinglot. 1989. Cesium-137 and Lead-210 in Alpine lake sediments: measurements and modelling of mixing processes. Journal of Geophysical Research. 94(C9), 12,761-12,770. September 15, 1989.

Marine Radioecology, Final report of the Nordic Nuclear Safety Research Project EKO-1, June 1998.

Snidvongs, A., G.M. McMurtry and S.V. Smith. 1992. Pb-210 and Cs-137 in sediments and soils of Tomales Bay Watershed, Northen California. Department of Oceanography, Univ. of Hawaii at Manoa Hololulu, HI 96822, U.S.A. Aug 1992.

Anderson, R.F., S.L. Schiff and R.H. Hesslein. 1987. Determining sediment accumulation and mixing rates using Pb-210, Cs-137, and other tracers: Problems due to postdepositional mobility or coring artifacts. Canadian Journal of Fisheries and Aquatic Sciences. 44(S1), 231-250.

Friedlander, Kennedy and Miller. 1964. Nuclear and Radiochemistry-2^nd Edition.

Mathieu, G.G. Appendix I - Rn²²²-Ra²²⁶ Technique of Analyses. 1977. Transport and transfer rates in the waters of the continental shelf. Contract EY 76-S-02-2185.

For additional information, contact Dr. Robert Flett at flett@flettresearch.ca

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