Search

Abstract Water can become contaminated as a result of a leak from a nuclear facility, such as a waste facility, or from clandestine nuclear activity. Low-level on-line radiation monitoring is needed to detect these events in real time. A Bayesian control chart method, Shiryaev-Roberts (SR) procedure, was compared with classical methods, 3- σ and cumulative sum (CUSUM), for quantifying an accumulating signal from an extractive scintillating resin flow-cell detection system. Solutions containing 0.10–5.0 Bq/L of 99Tc, as T 99 cO 4 − were pumped through a flow cell packed with extractive scintillating resin used in conjunction with a Beta-RAM Model 5 HPLC detector. While T 99 cO 4 − accumulated on the resin, time series data were collected. Control chart methods were applied to the data using statistical algorithms developed in MATLAB. SR charts were constructed using Poisson (Poisson SR) and Gaussian (Gaussian SR) probability distributions of count data to estimate the likelihood ratio. Poisson and Gaussian SR charts required less volume of radioactive solution at a fixed concentration to exceed the control limit in most cases than 3- σ and CUSUM control charts, particularly solutions with lower activity. SR is thus the ideal control chart for low-level on-line radiation monitoring. Once the control limit was exceeded, activity concentrations were estimated from the SR control chart using the control chart slope on a semi-logarithmic plot. A linear regression fit was applied to averaged slope data for five activity concentration groupings for Poisson and Gaussian SR control charts. A correlation coefficient (R 2) of 0.77 for Poisson SR and 0.90 for Gaussian SR suggest this method will adequately estimate activity concentration for an unknown solution. Highlights • Shiryaev-Roberts (SR) procedure uses less volume than classical control charts. • Poisson SR uses least volume but could be confused as a false positive. • Gaussian SR has low false positive rate and continuous increasing trend. • Activity concentration can be estimated from SR control chart slope. [ABSTRACT FROM AUTHOR]

Abstract: New dual functionality scintillating anion-exchange resins were developed for selective determination of 99TcO4 − in various natural freshwater samples. Stable scintillating particles were formed by preparing the vinyl monomer 2-[4-(4′-vinylbiphenylyl)]-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (vPBD), starting with the commercial organic flour TBut-PBD and its subsequent copolymerization with styrene, divinylbenzene, and p-chloromethylstyrene mixture. To integrate the radiochemical separation and radiometric detection steps within the same bead, the chloromethyl groups of the scintillating resins were subjected to amination reactions with dioctylamine (DOA) and trioctylamine (TOA). On-line quantification of 99TcO4 − was achieved by packing the scintillating anion-exchange resin into Teflon tubing for quantification by a flow scintillation analyzer (FSA). The two functionalized resins were selective for pertechnetate over the common anions in natural freshwaters, especially Cl− and SO4 2− with up to 1000 ppm and with up to 10 ppm I− and Cr2O7 2−. The uptake efficiency of the TOA sensor decreased from 97.88% to 85.08% in well water and river water, respectively, while the counting efficiency was almost constant (69.50%). The DOA performance showed lower efficiency in the two water types relative to TOA. On the other hand, the DOA sensor could be regenerated by 5 M HNO3 for reuse at least four times without losing its chemical or optical performance. The detection limit was 1.45 Bq which could be achieved by loading 45 mL from well and tap water containing the maximum contaminant level (MCL) of 99Tc (33 Bq/L). [Copyright &y& Elsevier]

Several types of bottled drinking water originating from three different areas in Egypt are studied through measurement of radium activity, assessment of related annual dose for adults and finally to define the role of water quality on radium levels. The mean levels of 226Ra activity range from 0.44 to 0.92Bq/L and the mean levels of 228Ra from 0.30 to 0.78Bq/L, with related 226Ra/228Ra ratios ranging from 2.61 to 0.56. Water types originating from the Eastern Nile Delta area are characterized by low 226Ra levels and relatively high 228Ra activity, presumably due to the muddy agricultural nature of this area, which is subject to water from several surface resources for irrigation. In general, the mean activity levels for both 226Ra and 228Ra are within those in drinking water in several other countries and the annual ingested dose is comparable with the typical range reported by UNSCEAR. Also, the effect of TDS, pH, calcium, bicarbonate, sulphate and chloride ion concentrations on radium levels is studied and discussed. [Copyright &y& Elsevier]