This work presents a low-level background gamma spectrometry system capable of achieving rapid determination of90Sr without chemical separation, in a soil sample when the90Sr to -ray emitting nuclide concentration ratio exceeds 10. The system consists of a highly efficient HPGe central detector operated in coincidence or anticoincidence with a NaI(Tl) guard detector and a NaI(Tl) backscatter detector. Experimental results indicate that the bremstrahlung radiation from a pure -emitter can be distinguished with respect to the differences in normal and coincidence spectra. The90Sr activity can be directly detemined in the sample in less than 1 hour with a minimum detectable concentration (MDC) estimated at 0.002 Bq·g–1 for a sample containing no appreciable -ray nuclides or other high energy, -emitting nuclides. In actual measurement, a 0.06 Bq·g–1 MDC for contaminated soils is achieved.
The effects of bentonite density and fulvic acid on the sorption and diffusion of 90Sr2+in compacted bentonite were investigated by using a capillary method. The experiments were carried out at pH 7.0±0.1 in the
presence of 0.01M NaClO4. The results suggest that the sorption and diffusion of 90Sr2+in compacted bentonite decreases with increasing the density of compacted bentonite. The presence of FA enhances the sorption
of Sr2+, but reduces the diffusion of Sr2+in compacted bentonite. The porosity of the compacted bentonite plays an important role in the sorption and diffusion behavior
of 90Sr2+. Using the calculated effective diffusion coefficients the long-term relative concentration distribution of strontium was
evaluated in compacted bentonite.
A method is described for the determination of89Sr and90Sr in samples of plant and animal origin. The Rehak-Feddersen method was modified to measure90Sr. Modification was made in the sample preparation and in the toluene-HDEHP [di(2-ethylhexyl)phosphoric acid] extraction.
After the extraction of yttrium, strontium is separated with nitric acid and—calculating with a correction factor—89Sr can directly be determined. Namely,89Sr can be measured in an aqueous solution by a liquid scintillation technique with an efficiency of 30% while90Sr with 1.4% only. Quenching of the solution—depending on the composition—which may influence the measurement of90Y and89Sr was also examined. Detection limits and reproducibilities are given. Finally, evaluation of the experimental data is reported.
Authors:R. Brodzinski, R. Runkle, J. Hartman, E. Ashbaker, M. Douglas, D. Jordan, K. McCormick, W. Sliger, and L. Todd
Migration of groundwater contamination from beneath the Hanford Site into the Columbia River creates a need for in situ 90Sr monitoring. The prototype monitor discussed here was designed for deployment downwell and provides near-real-time determination
of the 90Sr concentration in a two-liter groundwater sample. This manuscript discusses the design, construction and preliminary results
for a prototype monitor. Calibration and testing results of the as-built system show qualitative agreement between simulated
predictions and experimental results. Downwell and laboratory tests demonstrate a sensitivity to 90Sr at concentrations below 8 pCi/l (0.3 Bq/1) at a 90% confidence level in measurement times of less than four hours.
A radiochemical procedure is described for the sensitive determination of89Sr and90Sr activity concentrations in soil and sediment samples. After leaching the sample with hydrochloric acid, Sr is separated from most of the soluble matrix constituents and Ca by solvent extraction using dicylclohexano-18-crown-6 in trichloromethane. After backextraction with a EDTA-solution (ethylene diamine tetra acetate), Sr is purified by several precipitation steps from traces of matrix constituents and radionuclides which might interfere the beta measurements of89Sr,90Sr and90Y. The detection limits are about 0.2 Bq/kg and 0.4 Bq/kg for90Sr and89Sr respectively. The procedure can be applied to all kind of environmental samples with small modifications of the sample preparation steps prior to analysis.
Methodologies for simultaneous analysis of 137Cs, 90Sr, 238Pu and 239+240Pu were developed and applied to seawater samples. 137Cs levels in Brazilian coastal seawater ranged from 0.12 to 4.7 Bq·m-3, for 90Sr from 2.0 to 8.6 Bq·m-3, for 239+240Pu from 0.8 to 4.5 mBq·m-3 and for 238Pu it was of 1.9 mBq·m-3. The artificial radioactivity levels in Brazilian seawater are typical values due to fallout deposition.
A method to determine the leachable content of90Sr in environmental samples has been developed and applied to samples contaminated by the Chemobyl fallout. It consists of the following main steps: (1) drying and ashing, (2) leaching, (3) extraction of90Y using HDEHP and (4) Cherenkov counting of90Y in the organic phase. The method is easy to carry out and with a careful evaluation of the radioactivity measurement, the method is reliable down to a practical detection limit of approximately 7 mBq leachable90Sr/g sample ash.
Authors:Tser-Min Chang, Shao-Chou Chen, Jwn-Yung King, and Shieh-Jun Wang
An improved and rapid method for determination of90Sr via its daughter nuclide,90Y, in aqueous samples from the low-level radioactive wastes by Cerenkov counting was established. This technique is applicable to beta particles maximum energies greater than 0.263 MeV in aqueous solution. A comparison of90Sr determination by Cerenkov counting and standard wet chemical separation techniques indicates a high degree of correlation and excellent agreement. For a 20 ml aqueous sample following the prescribed experimental conditions and a 60 min counting interval, the detection limit was 0.20 dpm/ml (0.10 pCi/ml), and the relative deviation is less then 5%.
After the Chernobyl accident high concentrations of radionuclides were found in Sweden in mushrooms and the contents of90Sr and137Cs were measured. The level of90Sr was generally low and, in proportion to137Cs, 2–3 orders of magnitude lower than in the fallut. The contents of137Cs varied among species and extreme local variations occurred. The ratio134Cs/137Cs diverged from other biological samples leading to the conclusion that old fallout was involved in the uptake.
The present procedure for analysing 90Sr combines the use of a non radioactive carrier with high pressure ion chromatography separation, conductivity detection
of the carrier and optimized external counting by liquid scintillation. This improvement with respect to traditional methods
led to a more rapid and efficient purification stage. The present work proves that activities of 90Sr as low as 3 Bq/L can be measured in highly contaminated pressurized water reactor primary coolant matrix without any observed
radiochemical interference. The approach shows promise for the analysis of other emitters of low energy radiation, or isotopes
subject to high background or matrix effects in a PWR primary coolant.