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  • Author or Editor: S. Joshi x
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Abstract  

A simple and rapid procedure is described by which actinides can be mounted in a form suitable for alpha-particle spectrometry without recourse to electrodeposition. The actinides are coprecipitated as fluorides with 100 g of lanthanum carrier from an acidic solution. The precipitate is mounted on a 0.1 -pore membrane filter containing LaF3 substrate, also prepared from 100 g of lanthanum. The resolution obtained using samples of pure radiotracers and of frations isolated from lake sediments is generally comparable to that afforded by the conventional electrodeposition technique. The coprecipitation yield is generally quantitative. The entire procedure can be completed in about 90 min.

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Abstract  

A simple method is described for the isolation and determination of plutonium isotopes in sediments. The method involves leaching of sample with nitric acid and subsequent separation of plutonium on an anion-exchange column. Major matrix elements and several potential radiochemical interferences are removed during 8M HNO3 sample loading on the column. Thorium is removed by thorough washing with 10M HCl. Plutonium (IV) is eluted with 4M HCl. Source for alpha-particle spectrometry is prepared by LaF3 coprecipitation technique at which stage a complete separation from uranium(VI) is also achieved. The entire analytical procedure is completed in about two days.

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Abstract  

A method is described for the non-destructive determination of210Pb and226Ra in sediments. The procedure is based on the direct counting of the 46.5-keV -ray of210Pb and the 351.9-keV -emission of214Pb. The self-absorption of the 46.5-KeV -ray is corrected using a technique involving direct gamma transmission measurements on sample and efficiency calibration standard. Several reference materials when assayed by the described method yielded results in general agreement with the certified values. The application of the method is illustrated through the analysis of the excess210Pb profile of a Lake Ontario sediment core.

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Abstract  

Radionuclide concentrations in digester sludge and effluent samples from Hamilton and Dundas sewage treatment plants, located at the western tip of Lake Ontario, have been determined by high-resolution γ-ray spectrometry. The radionuclides51Cr,75Se and131I, which are used in nuclear medicine procedures, were found in sludge samples. Very low concentrations of51Cr, entering Lake Ontario through the Hamilton plant effluent discharge, have little effect on lake water quality.

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Abstract  

A method is described for the determination of228Th,230Th, and232Th in environmental samples from uranium mining and milling operations. The analytical procedure is based on the direct determination of228Th in the sample by high resolution γ-spectrometry followed by extraction and purification of the thorium fraction using high molecular weight amines and an anion-exchange technique, respectively, prior to α-spectrometry to determine isotopic ratios. The lowest level of detection for each thorium isotope is 0.01 pCi/g for solid samples and 20 pCi/l for aqueous samples. Replicate analyses of a typical mine waste stream gave a standard deviation of ±3% for228Th. Standard deviations of the230Th and232Th increased to ±11% apparently due to traces of210Po interfering in the α-spectrometry.

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Abstract  

210Pb,226Ra and137Cs profiles have been measured for sediment cores from three locations in Bay of Quinte, Lake Ontario, Canada. Compaction of the sediment with depth of burial is taken into account in calculating recent sedimentation rates and age profiles at these locations from the excess210Pb profiles. The rates are 1.803+0.592 cm·y–1 (0.254±0.083 g·cm–2·y–1), 0.101±0.017 cm·y–1 (0.036+0.006 g·cm–2·y–1), and 0.795±0.218 cm·y–1 (0.076±0.021 g·cm–2·y–1). The corresponding fluxes of excess210Pb to sediment/water interface are determined to be 1.652, 0.253, and 1.123 pCi·cm–2·y–1, respectively. The anomalies observed in the radionuclide concentration profiles are attributed to physical mixing. It is postulated that the significantly higher flux of210Pb observed at one of the locations is due to inputs from Trent River which joins the Bay near this location.

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Abstract  

The chemistry of uranium and its eight associated daughters has been considered in Lake Ontario water along with that of selected transuranic elements. These transuranics arise mainly from fallout, and to a lesser extent from nuclear fuel reprocessing. Most exist as free ions or oxides of various kinds, uranium probably exists as a strong uranyl carbonate complex.

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Abstract  

A scenario is presented for the transport of the Chernobyl radioactive debris across Canada and the Arctic. It is based on the analysis of the103Ru/137Cs ratios in terms of the Chernobyl release pattern. The ratios which ranged from 0.2 to more than 4.0 were associated with four different phases of the Chernobyl emissions which lasted 10 days, from April 26 to May 6, 1986. Debris from the initial phase /ratios of 0.2 to 0.5/ and the last phase /ratios above 2.5/ would have entered Canada on a very broad front extending from northern Quebec to the North West Territories by way of Greenland and the Arctic; debris from the second phase /ratios of 0.5 to 2.0/ and the third phase /ratios of 2.0 to 2.5/ would have entered Canada from the west after travelling by way of northern Siberia and the Bering Sea.

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Abstract  

Basic formulations used in the sedimentary210Pb dating technique are derived from fundamental considerations. The formulations are applicable to models that assume either a constant rate of supply (CRS) of unsupported210Pb to the sediments or a constant initial concentration (CIC) of this210Pb in the sediments. A previously proposed expression linking age discrepancy to mass sedimentation rates afforded by the two models is found to be inadequate in explaining the observed discrepancy between the CIC and CRS ages of segments of an undisturbed sediment core. It is noted that this age discrepancy is attributable to the mathematical treatment of data in the two models. A new expression, relating age discrepancy to the fluxes of unsupported210Pb obtainable by the two models, is derived and found to give more accurate and consistent results.

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Abstract  

Low-energy -ray spectrometry is used to detect fallout155Eu and207Bi in a210Pb-dated sediment core from McKay Lake, Ottawa, Canada. Unlike207Bi which is detected only in two core sections deposited in the mid 1970's,155Eu is consistently detectable to mid 1960's. A comparison of corresponding137Cs and155Eu inventories in the sediment core indicates that fallout155Eu derives primarily from the thermal neutron fission of235U. The derived flux of unsupported210Pb at the sediment/water interface is in agreement with previously estimated flux of atmospheric210Pb in the Great Lakes region.

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