A laboratory information management system for the analysis of tritium (3H) in environmental waters.

Accurate and precise measurements of low levels of tritium (3H) in environmental waters are difficult to attain due to complex steps of sample preparation, electrolytic enrichment, liquid scintillation decay counting, and extensive data processing. We present a Microsoft Access™ relational database application, TRIMS (Tritium Information Management System) to assist with sample and data processing of tritium analysis by managing the processes from sample registration and analysis to reporting and archiving. A complete uncertainty propagation algorithm ensures tritium results are reported with robust uncertainty metrics. TRIMS will help to increase laboratory productivity and improve the accuracy and precision of 3H assays. The software supports several enrichment protocols and LSC counter types. TRIMS is available for download at no cost from the IAEA at www.iaea.org/water.

Investigation of Workplace-like Calibration Fields via a Deuterium-Tritium (D-T) Neutron Generator.

Radiation survey meters and personal dosimeters are typically calibrated in reference neutron fields based on conventional radionuclide sources, such as americium-beryllium (Am-Be) or californium-252 (Cf), either unmodified or heavy-water moderated. However, these calibration neutron fields differ significantly from the workplace fields in which most of these survey meters and dosimeters are being used. Although some detectors are designed to yield an approximately dose-equivalent response over a particular neutron energy range, the response of other detectors is highly dependent upon neutron energy. This, in turn, can result in significant over- or underestimation of the intensity of neutron radiation and/or personal dose equivalent determined in the work environment. The use of simulated workplace neutron calibration fields that more closely match those present at the workplace could improve the accuracy of worker, and workplace, neutron dose assessment. This work provides an overview of the neutron fields found around nuclear power reactors and interim spent fuel storage installations based on available data. The feasibility of producing workplace-like calibration fields in an existing calibration facility has been investigated via Monte Carlo simulations. Several moderating assembly configurations, paired with a neutron generator using the deuterium tritium (D-T) fusion reaction, were explored.

(3)H activity comparison between FTMC, VNIIM and LNE-LNHB.

An activity comparison of tritiated water was organized in 2013 between 3 laboratories: FTMC (Lithuania), LNE-LNHB (France) and VNIIM (Russia). The solution was prepared by LNHB and ampoules were sent to the others laboratories. This solution was standardized in terms of activity per unit mass by participant laboratories using the Triple to Double Coincidence Ratio (TDCR) method in liquid scintillation counting (LSC). The tritiated water solution is traceable to the solution prepared by LNHB for the CCRI(II)-K2.H-3 2009 (3)H international comparison.

On the stochastic dependence between photomultipliers in the TDCR method.

The TDCR method (Triple to Double Coincidence Ratio) is widely implemented in National Metrology Institutes for activity primary measurements based on liquid scintillation counting. The detection efficiency and thereby the activity are determined using a statistical and physical model. In this article, we propose to revisit the application of the classical TDCR model and its validity by introducing a prerequisite of stochastic independence between photomultiplier counting. In order to support the need for this condition, the demonstration is carried out by considering the simple case of a monoenergetic deposition in the scintillation cocktail. Simulations of triple and double coincidence counting are presented in order to point out the existence of stochastic dependence between photomultipliers that can be significant in the case of low-energy deposition in the scintillator. It is demonstrated that a problem of time dependence arises when the coincidence resolving time is shorter than the time distribution of scintillation photons; in addition, it is shown that this effect is at the origin of a bias in the detection efficiency calculation encountered for the standardization of (3)H. This investigation is extended to the study of geometric dependence between photomultipliers related to the position of light emission inside the scintillation vial (the volume of the vial is not considered in the classical TDCR model). In that case, triple and double coincidences are calculated using a stochastic TDCR model based on the Monte-Carlo simulation code Geant4. This stochastic approach is also applied to the standardization of (51)Cr by liquid scintillation; the difference observed in detection efficiencies calculated using the standard and stochastic models can be explained by such an effect of geometric dependence between photomultiplier channels.

Drinking water standard for tritium-what's the risk?

This paper presents an assessment of lifetime risks of cancer incidence associated with the drinking water standard for tritium established by the U.S. Environmental Protection Agency (USEPA); this standard is an annual-average maximum contaminant level (MCL) of 740 Bq L(-1). This risk assessment has several defining characteristics: (1) an accounting of uncertainty in all parameters that relate a given concentration of tritium in drinking water to lifetime risk (except the number of days of consumption of drinking water in a year and the number of years of consumption) and an accounting of correlations of uncertain parameters to obtain probability distributions that represent uncertainty in estimated lifetime risks of cancer incidence; (2) inclusion of a radiation effectiveness factor (REF) to represent an increased biological effectiveness of low-energy electrons emitted in decay of tritium compared with high-energy photons; (3) use of recent estimates of risks of cancer incidence from exposure to high-energy photons, including the dependence of risks on an individual's gender and age, in the BEIR VII report; and (4) inclusion of risks of incidence of skin cancer, principally basal cell carcinoma. By assuming ingestion of tritium in drinking water at the MCL over an average life expectancy of 80 y in females and 75 y in males, 95% credibility intervals of lifetime risks of cancer incidence obtained in this assessment are (0.35, 12) × 10(-4) in females and (0.30, 15) × 10(-4) in males. Mean risks, which are considered to provide the best single measure of expected risks, are about 3 × 10(-4) in both genders. In comparison, USEPA's point estimate of the lifetime risk of cancer incidence, assuming a daily consumption of drinking water of 2 L over an average life expectancy of 75.2 y and excluding an REF for tritium and incidence of skin cancer, is 5.6 × 10(-5). Probability distributions of annual equivalent doses to the whole body associated with the drinking water standard for tritium also were obtained. Means and 97.5th percentiles of maximum annual doses to females and males, which occur at age <1 y, all are less than the annual equivalent dose of 40 µSv used by USEPA to establish the MCL.

Activity standardization of 3H with the new TDCR system at PTB.

A triple-to-double coincidence ratio (TDCR) liquid scintillation counting system (Pochwalski et al., 1988; Grau Malonda and Coursey, 1988) was set up at the Physikalisch-Technische Bundesanstalt (PTB) to be used as an additional technique for primary activity standardization. The optical chamber of the system was designed in our laboratory, expending great effort to achieve maximum light transmission to the photomultiplier tubes (PMT) and, consequently, a maximum counting efficiency and low uncertainties. A programme to compute the counting efficiencies and to analyse the measurement data was developed and tested. The software can also be used to allow for PMT asymmetries. The system and recently developed analysis procedures were used for the activity standardization of a tritiated water solution within the scope of an international comparison under the auspices of the Bureau International des Poids et Mesures (BIPM).

Half-life evaluations for 3H, 90Sr, and 90Y.

A recent paper has reviewed methods for the evaluation of discrepant sets of data and demonstrated the results of applying these methods to the published half-life data of 90Sr and 137Cs [MacMahon, T.D., Pearce, A., Harris, P., 2004. Convergence of techniques for the evaluation of discrepant data. Appl. Radiat. Isot. 60, 275-281]. The half-life data for 3H has been subject to a comprehensive review and critical evaluation by Lucas and Unterweger [2000. Comprehensive review and critical evaluation of the half-life of tritium. J. Res. Natl. Inst. Stand. Technol. 105, 541-549]. The current paper reports the results of applying the various evaluation procedures of MacMahon et al. Convergence of techniques for the evaluation of discrepant data. Appl. Radiat. Isot. 60, 275-281] to the data of Lucas and Unterweger [Comprehensive review and critical evaluation of the half-life of tritium. J. Res. Natl. Inst. Stand. Technol. 105, 541-549], resulting in a recommended half-life of 4497(4) days. MacMahon et al. [Convergence of techniques for the evaluation of discrepant data. Appl. Radiat. Isot. 60, 275-281] highlighted problems in the evaluation of the discrepant half-life data of 90Sr, in particular the worrying upward trend in the data, where the weighted mean of all the measurements increases, on average, by 35 days each time a new measurement result is added. The current paper reports on further analyses of these data. New measurements of the half-life of 90Y have been reported by Kossert and Schrader [2004. Standardization by liquid scintillation counting and half-life measurements of 90Y. Appl. Radiat. Isot. 60, 741]. This has prompted a new evaluation of all available published 90Y half-life data. The data are fairly consistent, and a value of 64.063(16) h is recommended.

Standardization of tritiated water by two improved methods.

Tritiated water has been standardized in the framework of a French-Romanian cooperation by two improved methods: liquid scintillation counting based on the triple to double coincidence ratio method and the internal gas proportional counting used in conjunction with a tritium generator for chemical reduction of water. The uncertainties of measurement for both methods were smaller than 0.6% and the two results were consistent within these uncertainties, indicating that either method is equally suited for standardizing tritiated water.

Multi-species assessment of electrical resistance as a skin integrity marker for in vitro percutaneous absorption studies.

Assessment of percutaneous absorption in vitro provides key information when predicting dermal absorption in vivo. Confirmation of skin membrane integrity is an essential component of the in vitro method, as described in test guideline OECD 428. Historically, assessment of the membrane's permeability to tritiated water (T2O) and the generation of a permeability coefficient (Kp) were used to confirm that the skin membrane was intact prior to application of the test penetrant. Measuring electrical resistance (ER) across the membrane is a simpler, quicker, safer and more cost effective method. To investigate the robustness of the ER integrity measure, the Kp values for T2O for a range of human and animal skin membranes were compared with corresponding ER data. Overall, for human, rat, pig, mouse, rabbit and guinea pig skin, the ER data gave a good inverse association with the corresponding Kp values; the higher the Kp the lower the ER values. In addition, the distribution across a large dataset for individual skin samples was similar for Kp and ER, allowing a cut-off value for ER to be established for each skin type. Based on CTL's (Syngenta Central Toxicology Laboratory) standard static diffusion cells and databridge, we propose that intact skin should have an ER equal to or above (in kOmega): human (10), mouse (5) guinea pig (5), pig (4) rat (3), and rabbit (0.8). We conclude that measurement of ER across in vitro skin membranes provides a robust measurement of skin barrier integrity and is an appropriate alternative to Kp for T2O in order to identify intact membranes that have acceptable permeability characteristics for in vitro percutaneous absorption studies.

Standardization of tritiated water and 204Tl by TDCR liquid scintillation counting.

The triple to double coincidence ratio method was used with a combined uncertainty of 1-2% to standardize tritiated water and a solution of 204Tl. The vial with liquid scintillator, in which the sample to be measured was dissolved, is optically coupled to three photomultipliers. The electronic module MAC-3 assures the selection of double and triple coincidences count rates, D and T, from the three counting channels. It contains the gating circuits, necessary to obtain the livetime value and the extended deadtime circuit. Specific computer programs were used to calculate the free parameter value, the efficiency of D and so, the value of the activity. The optimal value of the Birks ionisation-quenching parameter, kB, was evaluated by changing the detection efficiency with grey filters. Three types of liquid scintillators, namely InstaGel, PPO+POPOP+Triton in toluene and Ultima Gold, were employed. 204Tl was measured in the frame of an international comparison organized by BIPM. For tritiated water a comparison was made with LNHB-Saclay; the relative difference between the obtained values for the massic activity was only 0.2%.

Quantitative film autoradiography for tritium: methodological considerations.

The details of quantitative film autoradiography for tritium using tritium plastic standards were examined with respect to 3 issues: tritium tissue equivalent (TE) calibration; correction of autoabsorption differences for gray and white matter; and the use of carbon-14 standard sources as a method for quantifying tritium tissue images. Both 3H-tissue and 3H-plastic sources produced linear log-log relationships of 3H-concentration (nCi/mg source weight) vs source optical density (OD) over a reproducible OD range (0.080-0.800). The curves for both 3H-tissue and 3H-plastic were parallel; uncalibrated 3H-plastic standards exhibited a 4-fold higher autoabsorption over 3H-tissue sources for OD values in the linear range. Using chloroform extraction of brains from rats treated with either [14C]deoxyglucose ([14C]DG) or [3H]deoxyglucose ([3H]DG), we found neither isotope loss nor redistribution after defatting (30% reduction of tissue dry weight). After chloroform extraction, the OD values from both gray and white matter structures containing carbon-14 were unaltered. Gray matter OD values increased by 28.7 +/- 5.6% (mean +/- S.D.) in structures containing tritium; white matter structures containing tritium exhibited a 115.9 +/- 29.3% increase in OD after chloroform extraction. The increase in OD after chloroform extraction was a fixed percent for any given tritium OD value from unextracted tissue when the value was within the linear range of 0.080-0.800 OD units. The magnitude of the higher white matter autoabsorption for tritium was confirmed using tritium impregnated cow brain pastes of variable gray/white mixtures. Chloroform extraction of tissue from [3H]DG treated rats was therefore a suitable procedure for direct correction of regionally heterogeneous autoabsorption of tritium. Finally, the rates of image generation for tritium and carbon-14 sources were compared. The rate of increase of OD with increasing exposure time was found to be equal for 3H-tissue and 3H-plastic images; sources of carbon-14 in plastic, however, exhibited more accelerated rates of image generation when compared to tritium sources (i.e. 3H- and 14C-images did not covary with exposure time). The effect of non-covariance on tritium TE calibrated standards was the overestimation of OD values for 14C-plastic standards with increasing times of exposure (comparison of 4 week images to 1 week images showed errors of 35-40%). Use of carbon-14 sources to quantify tritium-generated images therefore required recalibration of 14C-plastic for all exposure times of interest.

Preparation of tritium standard gas by the use of tritiated methane.

Tritium standard gas for calibrating radioactivity detectors was prepared by the use of tritiated methane synthesized by the reaction of tritiated water with aluminum carbide at ca. 470 degrees C. A long-path proportional counter was used to standardize the radioactivity of the prepared gas. Tritiated gas of less than 10(4) Bq could be measured by this counter with the overall error of 3.5% (3 sigma). Finally, two types of standard were prepared in a metal cylinder and a glass ampoule. The latter type could be used as a handy calibration source for detectors.