Detection Capability of 89Sr and 90Sr Using Liquid Scintillation Counting.

ABSTRACT: We developed a new method for simultaneous determination of 89Sr and 90Sr with an emphasis on detectability. The samples were digested, and Sr was chemically purified followed by a single count on a liquid scintillation counter in three windows overlapping the 90Sr, 89Sr, and 90Y peaks. Gamma spectrometry was used to measure 85Sr, added for chemical recovery. The method was tested on 18 water samples spiked at levels from 9 to 242 Bq of 89Sr and 90Sr, with either single radionuclides or their mixtures. In addition, eight method blanks were measured. The data were analyzed numerically by solving a system of linear equations for 89Sr and 90Sr activities as analytes and 90Y activity as a participating component. The total uncertainties of the results were calculated numerically using variances and covariances. The average bias from the known activities was -0.3% (range from -3.6 to 3.1%) for 90Sr and - 1.5% (range from -10.1 to 5.1%) for 89Sr. The En-scores were within -1.0 and 1.0 at 95% confidence level. The detection capabilities of this method were determined by means of the decision threshold LC and the limit of detection referred to as the minimum detectable activity. All relevant uncertainties were propagated into the LC and minimum detectable activity. In addition, detection limits were calculated for the purpose of Safe Drinking Water Act monitoring. The detection capabilities were compared with the regulatory requirements in the US and EU for food and water. For samples spiked with either pure 89Sr or 90Sr, false positives were observed for the opposite radionuclide exceeding the above LC values. This was attributed to interference by the spiked activity. A new method was developed to calculate decision and detectability curves in the presence of interference.

Gamma Radioactivity Detection Limits and Associated Radionuclide Intakes Study in Artificial Human Urine Using Sodium-iodide and High-purity Germanium Detectors.

ABSTRACT: The performance of several gamma detectors was investigated for emergency urine bioassay screening of two radionuclides of concern: 131 I and 137 Cs. Unspiked artificial urine samples were measured for 10 min each on four different gamma detectors: 80% relative efficiency high-purity Ge detector in standard shielding, 102% low-background high-purity Ge detector equipped with top muon shield, 78% high-purity Ge well detector in standard shielding, and 4″ × 4″ NaI well detector in standard shielding. The measured gamma spectra were analyzed in two ways: (1) for the 364-keV peak region of 131 I and 662-keV peak region of 137 Cs and (2) for the total counts in the full energy spectrum (50-2,048 keV). The results were analyzed using the principles of signal detection theory according to the Currie's formalism extended by a complete uncertainty propagation. This enabled calculation of the detection capability in terms of detection limit (Bq L -1 ) of urine, the latter referred to as minimum detectable activity. The NaI well detector had the lowest minimum detectable activities for total spectra, whereas the high-purity Ge well detector had the lowest peak minimum detectable activity values. Minimum detectable inhalation and ingestion intakes from urine bioassay were calculated from the minimum detectable activity values for urine collection 1 d, 1 wk, and 1 mo past the initial intake. The calculated intakes were compared with annual limits on intake. The results are interpreted with respect to a large-scale radiological emergency response.

A Combined Density Functional Theory and Spectrophotometry Study of the Bonding Interactions of [NpO2·M]4+ Cation-Cation Complexes.

The equilibrium constants for [NpO2·M]4+ (M = Al3+, In3+, Sc3+, Fe3+) in µ = 10 M nitric acid and [NpO2·Ga]4+ in µ = 10 M hydrochloric acid media have been determined. The trend in the interaction strength follows: Fe3+ > Sc3+ ≥ In3+ > Ga3+ ≫ Al3+. These equilibrium constants are compared to those of previously reported values for NpO2+ complexes with Cr3+ and Rh3+ within the literature. Thermodynamic parameters and bonding modes are discussed, with density functional theory and natural bond orbital analysis indicating that the NpO2+ dioxocation acts as a π-donor with transition-metal cations and a σ-donor with group 13 cations. The small changes in electron-donating ability is modulated by the overlap with the coordinating metal ion's valence atomic orbitals.