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  • Author or Editor: T. DeVol x
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Abstract  

Statistical control charts are presented for the evaluation of time series radiation counter data from flow cells used for monitoring of low levels of 99TcO4 in environmental solutions. Control chart methods consisted of the 3-sigma (3σ) chart, the cumulative sum (CUSUM) chart, and the exponentially weighted moving average (EWMA) chart. Each method involves a control limit based on the detector background which constitutes the detection limit. Both the CUSUM and EWMA charts are suitable to detect and estimate sample concentration requiring less solution volume than when using a 3σ control chart. Data presented here indicate that the overall accuracy and precision of the CUSUM method is the best.

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Self Assembled Monolayers on Mesoporous Supports (SAMMS) are nanostructured silica sorbents that offer fast uptake kinetics, high material loading, and excellent selectivity. We have found that these materials rapidly preconcentrate radionuclides from solution and enable direct assay. We will discuss the utilization of SAMMS for measurement of alpha-, beta- and gamma-emitters. The issues involved in direct counting of SAMMS with various methods are explored. We will discuss the advantages, challenges, and limitations involved in using SAMMS for radiochemical analysis.

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Summary  

A new flow-cell detection system using a TeflonÒcoated passivated ion-implanted planar silicon semiconductor detector was developed for detection of pertechnetate (99TcO4 - E b

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Abstract  

For characterizing radioactive samples there are two major considerations in the application of a coupled liquid chromatography and on-line scintillation counting system: (1) radiological interferences and (2) chemical interferences from the matrix. A study was conducted to identify which interferences from typical matrices found at several Department of Energy facilities affected the separation of a radioactive tracer solution by the coupled system. The selection of potential interferent materials was determined through a review of characterization and monitoring studies of surface water, ground water, and high level waste tank supermatant at those facilities. Incremental mass loadings of contaminant were mixed with a standardized radioactive tracer (55Fe,63Ni,90Sr and147Pm) and then injected into a coupled system. The resultant chromatograms were compared to the chromatogram of the standard radionuclide solution to determine the effects of the chemical or radiological constituent. Relative to the radionuclide solution,137Cs was the only activation/fission product used in this study to effect a radiological interference. For the natural uranium series, a radiological interference was observed for90Sr due to either a uranium isotope or a decay product of the series. No rad interference was observed from228Th, though it must be noted that the elution program was not capable of completely separating the decay series nuclides of natural uranium or thorium. For the chemical interferences, the effects are twofold since the chemical can affect the concentration of ions on the pre-concentration stage as well as the chromatographic separation. The general trend observed was that increasing the ionic strength of the chemical resulted in decreased retention fractions on the pre-concentration column and significant shifts in peak elution times.

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Abstract  

A prompt gamma-ray neutron activation analysis (PGNAA) system was used to calibrate and validate a Monte Carlo model as a proof of principle for the quantification of chlorine in soil. First, the response of an n-type HPGe detector to point sources of 60Co and 152Eu was determined experimentally and used to calibrate an MCNP4a model of the detector. The refined MCNP4a detector model can predict the absolute peak detection efficiency within 12% in the energy range of 120–1400 keV. Second, a PGNAA system consisting of a light-water moderated 252Cf (1.06 g) neutron source, and the shielded and collimated HPGe detector was used to collect prompt gamma-ray spectra from Savannah River Site (SRS) soil spiked with chlorine. The spectra were used to calculate the minimum detectable concentration (MDC) of chlorine and the prompt gamma-ray detection probability. Using the 252Cf based PGNAA system, the MDC for Cl in the SRS soil is 4400 g/g for an 1800-second irradiation based on the analysis of the 6110 keV prompt gamma-ray. MCNP4a was used to predict the PGNAA detection probability, which was accomplished by modeling the neutron and gamma-ray transport components separately. In the energy range of 788 to 6110 keV, the MCNP4a predictions of the prompt gamma-ray detection probability were generally within 60% of the experimental value, thus validating the Monte Carlo model.

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Abstract  

The use of ion chromatography and on-line scintillation counting for the measurement of non-gamma emitters was evaluated for its applicability to reactor coolant. Potential chemical and radiological interferences were identified and a procedure was developed to eliminate them. The method was tested on a sample of simulated pressurized water reactor coolant.

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Abstract  

A system using an ion chromatograph coupled to a flow-cell scintillation detector for rapidly measuring the oxidation states of actinides at low concentrations (<10–6M) in aqueous solutions was evaluated. The key components of the system are a cation–anion separation column (Dionex, CS5) and a flow cell detector with scintillating cerium activated glass beads. The typical procedure was to introduce a 0.5 ml aliquot of sample spiked with actinides in the +III to +VI oxidation states into a 5 ml sample loop followed by 4 ml of synthetic groundwater simulant. Separation was achieved at a flow rate of 1 ml/min using an isocratic elution with oxalic, diglycolic, and nitric acids followed by distilled water. Tests were first conducted to determine elution times and recoveries for an acidic solution (pH 2) and a ground water simulant (pH 8) containing Am(III), Pu(IV), Th(IV), Pu(V), and U(VI). Then, an analysis was performed using a mixture of Pu(IV), Pu(V), and Pu(VI) in the ground water simulant and compared to results using the DBM extraction technique. Approximate elution times were the same for both the acidic solution and the ground water simulant. These were as follows: Pu(V) at 10 min, Am(III) at 15 min, Pu(IV) at 25 min, Th (IV) at 28 min and U(VI) at 36 min. Recoveries for the acidic solution were quantitative for U(VI) and Th(IV) and exceeded 80% for Am(III). Recoveries for the ground water simulant were quantitative for U(VI), but they were generally not quantitative for Th(IV), Pu(IV), and Am(III). For Th(IV) and Pu(IV), less than quantitative recoveries were attributed to the formation of neutral hydroxides and colloids; for Am(III) they were attributed to insoluble carbonates and/or hydroxycarbonates. When applied to the measurement of plutonium in the ground water simulant, the technique provided showed good agreement with the dibenzoylmethane (DBM) extraction technique, but it could not distinguish between Pu(V) and Pu(VI). This was likely due to the reduction of Pu(VI) to Pu(V) in the sample by the oxalic acid eluent. However, in spite of this limitation, the technique can be used to distinguish between Pu(IV) and Pu(V) in aqueous environmental samples within a pH range of 4 to 8 and an E H range of -0.2 to 0.6 V, the predominance region for Pu(III), (IV), and (V). In addition, this technique can be used to corroborate oxidation state analysis from the dibenzoylmethane (DBM) extraction method for environmental samples.

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Summary  

A technique is presented for the relatively rapid measurement of actinide and beta-emitting radionuclides in waste streams and environmental samples. It uses ion chromatography for elemental selectivity and flow-through scintillation counting with dual parameter pulse-height and pulse-shape analysis for alpha/beta detection and discrimination. The system was tested for one surrogate sample (spiked groundwater from the southeastern U.S.) and two actual samples from the Savannah River Site (supernatant from a highactivity drain tank and sludge from a high level waste tank). For the spiked groundwater, recoveries were quantitative for all of the analytes (americium, curium, plutonium, and strontium) except uranium. For the actual samples, which contained americium, curium, plutonium, strontium, and cesium, the results using the system were within 20% of those obtained independently. Based on these tests, it is concluded that the system is capable of analyzing alpha- and beta-emitting radionuclides in samples that are representative of those encountered at contaminated former weapons sites.

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Abstract  

An extraction procedure utilizing alpha liquid scintillation was evaluated for the rapid determination of uranium in aqueous environmental samples. The extraction efficiency of the system was measured under varying chemical conditions including pH. The procedure was evaluated against a traditional radiochemical technique using both laboratory prepared control samples and actual groundwater. Finally, the possibility of obtaining isotopic information from the liquid scintillation spectra was also investigated using a curve fitting routine.

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