Methodology for rapid tritium determination in urine

Summary The present work proposes a methodology for a rapid determina-tion of the tritium content in urine. The urine is treated with active carbon and tritium is determined by liquid scintillation counting. Different kinds of active carbon were experimented for the metabolites removal from urine samples. The counting efficiency was calculated by a quench curve using yellow food dye as a quenching agent. It was obtained a procedure which maintained a good reproducibility, low uncertainty and detection limit of 7 Bq/l (10 ml of urine, 120 minutes of counting time and efficiency of 23.9%).     

A spectral overlap method for self monitoring quench correction in double isotope liquid scintillation counting

A method for quench correction of samples with double radioactive labelling is described. Each nuclide makes a contribution to the counting rate of three channels of a liquid scintillation counter. This channel overlap is an essential requirement of the calibration procedure rather than a limitation, and allows more freedom in the choice of counting conditions. After calibration with suitable standards the method will tolerate wide variations in the ratio of one isotope to the other extending to single label samples of either isotope. This is the outstanding advantage over the channel ratio method which requires a statistically significant counting rate for the higher energy isotope. The method takes advantage of the facilities offered by a computer which may be on line or remote.¹⁴C and tritium are used to demonstrate the utility of the method.     

Optimisation of liquid scintillation counting conditions for rapid tritium determination in aqueous samples

Several studies were carried out to optimise rapid tritium analysis in fresh waters by ultra-low background liquid scintillation. These included the optimisation of (1) sample/scintillant ratio, (2) pulse shape analysis, and (3) pulse-amplitude comparator, and studies concerning (1) the combination scintillant/vial and (2) the effect of chemiluminescence. The proposed method involves the mixing of 8 ml sample with 12 ml scintillation cocktail Ultima Gold AB in Zinsser low diffusion vials. These are stored during one day before counting in order to reduce chemiluminescence. The minimum detectable activity achieved was 2.2 Bq·l⁻¹ for a total counting time of 360 minutes. In order to test the method, tritium was determined in Ebro river samples.     

Method for rapid tritiated water extraction from environmental samples

We have developed a thermal vacuum desorption process to rapidly extract water from environmental samples for tritium analysis. Thermal vacuum desorption allows for extraction of the moisture from the sample within a few hours in a form and quantity suitable for liquid scintillation counting and allows detection of tritium at the levels of <2 Bq/l of milk, <0.5 Bq/g of vegetation, and <0.5 Bq/g of soil. We developed a prototype unit that can process batches of twenty or more samples within 24 hours. Early data shows that a high percentage of water is extracted reproducibly without enrichment or depletion of the tritium content. The quench coefficient of the extracted water is low allowing for accurate, direct liquid scintillation counting. In most samples, good comparison has been observed with results using freeze-dry lyophilization as the water extraction method     

Ultraviolet photolysis of urine for suppression of color quenching prior to liquid scintillation counting of tritium

In order to reduce the color quenching in the measurement of tritium in urine by liquid scintillation counting , UV irradiation was applied to decompose the organic substances in the sample. Urine was decolorized under UV irradiation in the presence of hydrogen peroxide. As a result, color quenching was considerably suppressed and higher counting efficiency of tritium was obtained. This UV treatment made it possible to increase the urine content in the sample from 2 to 40% (v/v) without significant decrease of counting efficiency. Either higher sensitivity or shorter analysis time was achieved in the tritium measurement by the augmentation of urine content. When the measurement time was 30 min, the detection limit of tritium defined as 3s was 0.03 Bq/ml. At the expense of some sensitivity (set at a detection limit of 0.3 Bq/ml), the measurement time was shortened to 0.5 min. These results will make a great improvement to routine tritium monitoring as well as to emergency monitoring in mass tritium exposure.      

A method for the determination of tritium distribution in environmental and biological samples

A method for the determination of the tritium distribution in environmental and biological samples is described. Tritium as HTO is removed by freeze-drying and the residue is combusted to obtain organically bound tritium. Each tritium fraction is electrolytically enriched and determined by liquid scintillation spectrometry. Enrichment and large sample sizes are required due to the low environmental tritium levels. During the analyses of more than 600 samples over a two-year period all aspects of the method (freeze-drying, combustion, enrichment and counting) have provided reproducible and precise results.     

Measurement of (90)Sr in environmental samples by cation-exchange and liquid scintillation counting

A new method for the measurement of (90)Sr in environmental samples by cation-exchange and liquid scintillation counting is described. Strontium carbonate is purified by precipitation and ion-exchange, weighed for the determination of chemical yield, dissolved in hydrochloric acid and mixed with the liquid scintillator, Aquasol-2. Two channels of a low-background liquid scintillation counter are used to determine (90)Sr, (90)Y and (89)Sr, free from the effects of environmental tritium. The values of (90)Sr obtained by this method are in good agreement with those from ordinary (90)Y milking and the gas proportional counting method. The concentration of (90)Sr in the air at Tokai-mura in Japan has been measured by the new method.     

Optimization of liquid scintillation counting techniques for the determination of carbon-14 in environmental samples

The goal of this work was to optimize the liquid scintillation counting techniques for the determination of¹⁴C in stack effluent gases and in environmental samples such as biological and air samples. Carbon-14 activities in most environmental samples were measured with the direct CO₂ absorption method. The highest figures of merit were found through the variation of Carbosorb E and Permafluor V ratio, and measurement windows. The best condition was an 1:1 volume ratio. Average 2.35 g of CO₂ was reproducibly absorbed in the 20 ml mixture within 40 minutes. The counting efficiency determined by repeated analysis of NIST oxalic acid standard and the background count rate were measured to be 58.8±1.4% and 1.88±0.06 cpm, respectively, in case of saturated solution. The correction curves of counting efficiency for partially saturated solutions and for saturated solutions with quenching were prepared, respectively. The overall uncertainty of the sample specific activity for near background levels was estimated to be about 7% for 4 hours counting at 95% confidence level. Stack effluent gas samples were measured by a gel suspension counting method. After precipitation of CO₂ in the form of BaCO₃, 140 mg of which was mixed with 6 ml H₂O and 12 ml of Instagel XF. The counting efficiency was measured to be 71.5±1.7% and the typical sensitivity of this technique was about 510 mBq/m³ for a 100 min count at a background count rate of 4.7 cpm. For the benzene counting method measurements were performed with a mixture of 3 ml benzene and 1 ml of scintillation cocktail (5 g of butyl-PBD in 100 ml of scintillation-grade toluene) in a low potassium 7 ml borosilicate glass vial. The counting efficiency and the background count rate were measured to be 64.3±1.0% and 0.51±0.05 cpm, respectively. The long-term stability of samples has been checked for all the counting techniques over a two week period, during which no apparent change in counting efficiency and background level was found.     

Measurement of tritium with plastic scintillators in large vials of a low background liquid scintillation counter: an organic waste-less method

The tritium compounds, tritiated water as a volatile compound and ³H-methionine as a non-volatile compound, were measured with two types of plastic scintillators (PSs) using a low background liquid scintillation counter (LSC). It is advantage that minimal organic waste is generated when a plastic scintillator is used for LSC measurement. The effect of large vials on counting efficiency, plasma effects with three types of plasma devices for PS-sheets, the effect of UV-light on PS-pellets, the relationship between the activity and the count rate, and the detection limits of tritium were studied with respect to the development of large-scale measurement systems.

     

Removal of the impurities from environmental water samples for tritium measurement by liquid scintillation counting

Liquid scintillation counting is the most popular method for tritium measurement, however, it takes much time and a lot of doing to distill off the impurities before mixing the sample water and liquid scintillation cocktail. We have investigated the possibility of an alternative method to the distillation. We have found out that the filtration can be an alternative to distillation for the environmental water samples before electrolytic enrichment.     

Low level alpha activity measurements with pulse shape discrimination--application to the determination of alpha-nuclides in environmental samples

Liquid scintillation counting of alpha rays with pulse shape discrimination was applied to the analysis of 226Ra and 239+240Pu in environmental samples and of alpha-emitters in/on a filter paper. The instrument used in this study was either a specially designed detector or a commercial liquid scintillation counter with an automatic sample changer, both of which were connected to the pulse shape discrimination circuit. The background counting rate in alpha energy region of 5-7 MeV was 0.01 or 0.04 cpm/MeV, respectively. The figure of merit indicating the resolving power for alpha- and beta-particles in time spectrum was found to be 5.7 for the commercial liquid scintillation counter.     

Radiochemical determination of lead-210 in environmental water samples using Cerenkov counting

A relatively simple method has been developed for the determination of²¹⁰Pb via its -emitting daughter,²¹⁰Bi. Lead-210 was separated from interfering elements as lead sulphate. The precipitate was dissolved in an alkaline solution of EDTA and the Cerenkov signal produced by the build-up of²¹⁰Bi was counted 30 days after storage using tritium channel of a liquid scintillation counter. Cerenkov counting efficiency was found to be approximately 20%. A lower limit of detection of 5.1 mBq/1 (based on 3 of the background with 500 minute counting time) was achieved. Chemical recoveries in the range of 70–100% were determined gravimetrically. Interference associated with currently used methods is avoided. Data from from both spiked samples and natural samples are presented.     

Neutron activation analysis of low level lithium in water samples

For determining low level lithium concentrations in water, a neutron activation method based on the measurement of tritium radioactivity produced by⁶Li(n,)³H reaction has been developed. This method is specific and free from interference by other chemical elements. Using a low background liquid scintillation counter for tritium measurement, the detection limit is approximately 0.3 ppm during irradiation at a thermal neutron flux density of 1.1·10⁷n·cm^–2·s^–1 for 6 hours by a small nuclear reactor and liquid scintillation counting for 2000 minutes     

Quantification of99Tc by liquid scintillation counting: An evaluation of chemical quenching by liquid chromatographic eluents

The feasibility of utilizing liquid scintillation counting as a detection method for the liquid chromatographic analysis of⁹⁹Tc is evaluated. The chemical quenching of constituents commonly found in liquid chromatographic mobile phases is investigated, and quench corrections are presented. Quantification of⁹⁹Tc is achieved over a concentration range of 10^–3 to 10^–8M on quiescent KTCO₄ solutions, with sample volumes of 0.3 ml, yielding a counting efficiency from 51 to 59% for a narrow 150 channel window. The potential for the double isotope labelling of technetium complexes and the implications of the liquid scintillation counting of⁹⁹Tc in flowing eluents are discussed.     

Volume reduction and tritium retention factor in electrolytic enrichment of water

Volume reduction(N), tritium retention factor (R), tritium concentration factor(Z) and apparent separation factor(beta) were measured on the large and small electrolytic cell systems. The relative variation of R was smaller than that of Z. So, it is recommended to use R in calculation of tritium concentrations in water samples. Furthermore, it was empirically revealed that R can be obtained only from N if a reliable beta-value is previously known. Therefore, it is possible to obtain R without electrolysis of the tritium standard solution. Taking into account the above facts, the so-called non-spike analysis of tritium, in which electrolytic enrichment and liquid scintillation counting are combined, becomes practicable.     

Tritium activity levels in drinking water of Adana,Turkey

Tritium activity in potable drinking water samples from Adana city were measured using liquid scintillation counting after distillation procedure. The results exposed that the activity concentrations of the tritium measured in one-third of these samples were lower than minimum detectable activity which has a value of 2 Bq/L for counting time of 1,500 min. However, the maximum and mean value of the tritium activity was found to be 9.1 Bq/L (77.3 TU) and 7.0 Bq/l (59.4 TU), respectively. These values were substantially below the 100 Bq/L which is normative limit in Turkey for waters intended for human consumption. The highest values of annual effective dose received by infants, children and adults due to measured tritium activity were estimated as 0.041, 0.057 and 0.120 μSv/y, respectively.     

Comparison of radiometric and non-radiometric methods for uranium determination in groundwater of Punjab,India

Uranium in groundwater samples collected from Punjab state, India was determined using radiometric methods (extractive liquid scintillation and Cerenkov counting). Experimental conditions were optimized by studying the effect of sample pH, quenching and amount of extracting agent added to the scintillation cocktail on recovery of uranium. To ensure the accuracy of results, both radiometric methods were compared with non radiometric method such as adsorptive stripping voltammetry and found to be very good agreement. The distinct advantage of proposed radiometric methods is almost 100 % effective especially extractive liquid scintillation for simultaneous measurement of alpha and beta emitting radionuclides with fast and simple sample preparation.     

Radioactivity measurement with a plastic scintillation vial

Liquid scintillation counting is widely used to measure radioactivity, but it generates radioactive organic liquid waste. Not to generate the liquid waste using a liquid scintillation counter, novel counting method with a plastic scintillation vial was designed. The counting efficiency for ³²P was 10–40% and that for ¹²⁵I was 4–8%. The efficiency depended on the sample volume. The color quenching effect was negligible. No radioactive liquid waste was generated by this method. In addition, you can reuse the measured sample.     

Development and validation of Ni–Ni electrolytic enrichment method for tritium determination in samples of underground waters of Jeju Island

A method of tritium electrolytic enrichment was developed, optimized and validated. The enrichment parameters were compared with different current and total current charge variation and tritium separation factor was from 8 to 36 with a current density variation. The detection limit of tritium measurement is about 0.5 TU using 1,000 mL sample and 600 min counting time. Several samples of groundwaters were processed in our and another laboratory with good agreement of results within 15% deviation. Developed and validated method of tritium determination was applied groundwaters in Jeju Island with a liquid scintillation counter (LSC) and electrolytic enrichment method using Ni–Ni electrodes. The tritium concentrations in fifty eight groundwaters in Jeju Island were ranged <0.5 TU-3.9 TU and averaged value was 2.12 TU.     

Study of kinetics,equilibrium and isotope exchange in ion exchanger systems

An automatic, rapid combustion method has been developed for the determination of tritium and¹⁴C in singly or doubly labelled organic materials by liquid scintillation counting. The sample is burned in a stream of oxygen. The water formed and its tritium content are retained from the gas stream in an absorber containing a small amount of diethyleneglycol monoethyl ether. Radioactive carbon dioxide, if included in the combustion products, is transferred into 3-methoxypropylamine. The final solutions ready for counting are obtained in less than three minutes. Quantitative collection recoveries for both tritium and¹⁴C are achieved and no cross-contamination occurs.