A method for the determination of tritium in environmental water samples by electrolytic enrichment

In order to determine the tritium concentration in environmental water samples, the electrolytic enrichment was carried out with (St) and without (S) addition of tritiated water of a certain concentration (deuterium-free) to the samples. With the use of the fundamental formulas on electrolytic enrichment, the deuterium concentration (Dit) before electrolysis for an environmental water sample is determined by liquid scintillation counting and densitometry for the sample St. Furthermore, the tritium concentration in the environmental water sample is determined by the above methods for the sample S, and by the substitution of Dit for Di in the formulas. Tritium concentrations in environmental water samples were found to be determined within an accuracy of 10% by this method when Vi/Vf was 14-25. It is considered that this method dispenses with the direct measurement of low deuterium concentrations (Di) before electrolysis, a special technique on the purification of water for densitometry, and moreover, excludes the possibility of cross contamination in the electrolytic enrichment by the spike cell method.     

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     

Tritium in organic matter around Krško Nuclear Power Plant

The aim of the research was to obtain first results of tritium in the organic matter of environmental samples in the vicinity of Kr?ko NPP. The emphasis was on the layout of suitable sampling network of crops and fruits in nearby agricultural area. Method for determination of tritium in organic matter in the form of Tissue Free Water Tritium (TFWT) and Organically Bound Tritium (OBT) has been implemented. Capabilities of the methods were tested on real environmental samples and its findings were compared to modeled activities of tritium from atmospheric releases and literature based results of TFWT and OBT.     

Uncertainty assessment of environmental tritium measurements in water

The method most widely used nowadays to measure environmental tritium levels in water is electrolytic enrichment followed by liquid scintillation spectrometry. Although these techniques have been in use for many years, there is a gap in systematic analysis of the sources of uncertainty associated with this particular application. The paper presents a comprehensive assessment of the individual uncertainty components of the entire analytical process, starting from sample preparation to radioactivity measurement. Examples of the complete uncertainty budget for typical tritium levels in the analysed water samples are included. The relative importance of individual uncertainty components is given and possible ways of improving the overall quality of analyses are discussed.     

Efficiency of tritium enrichment by electrolytic cell with multi-nickel-plates electrode and its application to the determination of tritium in environmental water

For the purpose of speeding up the tritium enrichment by electrolysis, we have produced an electrolytic cell with the multi-plate-electrode system instead of the commonly used single-plate-electrode, and examined the efficiencies for the tritium enrichment under the conditions of different current densities and electrode gaps. From the results, the tritium recovery and the separation factor beta were found to be maximized under the condition of 70 mA/cm2 of current density and 1.6 mm of electrode gap, and they were 90 percent and 23, respectively. Using this cell, it took 28 hours to reduce 100 ml of a sample water to 10 ml, and took 2 days, including the time required for other operations, to determine the tritium concentration of 1.85 Bq/l (50 pCi/l) with the counting error of within +/- 10 percent. This method has been applied to determining the tritium concentrations of environmental samples from Yamato River region during July 1981-February 1983. They were in the range of 1.11-9.48 Bq/l (30-256 pCi/l).     

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.     

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.     

Tritium in Lebensmitteln

In order to test the method of tritium determination and to determine the tritium activity, foods of known origin were investigated. The accuracy of the method over a prolonged period of time is confirmed by the statistical evaluation of the background values and of the counting efficiency. An average value of 600–800 pCi of tritium in one litre of water was found in milk, potatoes and apples. Drinking water contained very different activities of tritium, depending on its origin as ground or surface water. Food samples from the environment of nuclear reactors were not different in their tritium content when compared to those of other origin.     

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.     

Effect of chemical quenching on background counting rate in tritium channel of a large volume liquid scintillation counter

Background counting rate in tritium channel of a large volume liquid scintillation counter increased with water content ranged 0 to 50% of liquid scintillator. This phenomenon can be explained as follows: The height of scintillation pulses of Compton electrons induced by background gamma radiation is lowered by chemical quenching and shifts to tritium channel. The background counting rate in tritium channel showed a linear relationship with external standard channel ratio of background samples. This relationship is applicable to determine the correct background counting rate for quenching samples and to achieve higher precision of tritium measurement.     

Recovery of tritium obtained as a by-product in the production of fluorine-18

For samples of irradiated natural and enriched (95%) Li₂CO₃, normal distillation to dryness of the alumina column eluates permits recuperation of approximately 80% of the tritium. The distilled samples were concentrated by electrolysis and a subsequent vacuum distillation resulted in a tritium enrichment of the order of 30%. The enriched samples were used to prepare sealed, calibrated sources, with different levels of tritium radioactivity, to be used as standards for the determination of tritium in unknown samples using liquid scintillation.     

Levels of tritium concentration in the environmental samples around JAERI TOKAI

By the operation of research reactors, tritium-handling facilities, nuclear power plants, and a reprocessing facility around JAERI TOKAI, tritium is released into the environment in compliance with the regulatory standards.To investigate the levels of tritium concentration in environmental samples around JAERI, rain, air (vapor and hydrogen gas), and tissue-free water of pine needles were measured and analyzed from 1984 to 1993. Sampling locations were determined by taking into consideration wind direction, distance from nuclear facilities, and population distribution. The NAKA site (about 6 km west-northwest from the TOKAI site) was also selected as a reference point.Rain and tissue-free water of pine needles were sampled monthly. For air samples, sampling was carried out for two weeks by using the continuous tritium sampler. After the pretreatment of samples, tritium concentrations were measured by a low background liquid scintillation counter (detection limit is 0.8 Bq/l).Annual mean tritium concentrations in rain observed at six points for 10 years was 0.8 to 8.9 Bq/l, which decreased with distance from the nuclear facilities. Tritium concentrations in rain obtained at Chiba City were around 0.8 Bq/l (1987–1988) and those at the NAKA site were 0.8 to 3.8 Bq/l.Annual mean HTO concentrations in air at three points for 10 years were 9.2×10^–2 to 1.1 Bq/m³, although HT concentrations in air, ranging from 1.7×10^–2 to 5.8×10^–2 Bq/m³, were not influenced by the operation of the nuclear facilities.Annual mean tritium concentrations in tissue-free water of pine needles at four points for 10 years were 1.4 to 31 Bq/l. Those at the NAKA site ranging from 1.4 to 6.2 Bq/l were in good agreement with the reported value by Takashima of 0.78 to 3.0 Bq/l at twenty-one locations in Japan.Monthly mean HTO concentrations in air for 10 years showed a good correlation with absolute humidity, while other samples showed no seasonal variation.Higher level tritium concentrations in rain, in air (vapor), and in tissue-free water of pine needles at the TOKAI site were caused by the tritium released from the nuclear facilities.The committed effective dose equivalent to the member of general public, estimated using the maximum tritium concentration in air (1.1 Bq/m³), was 0.23 Sv, which was about 1/4000 of dose limit for general public.     

升温方式对真空冷冻干燥过程的影响

为了在保证冻干样品品质的同时缩短冻干时间,以猪主动脉为研究对象进行真空冷冻干燥.采用阶段升温方式与传统地一次干燥和二次干燥方式进行对比,结合脱水率、外观形态和力学性能,探讨阶段升温方式对缩短冻干时间的影响.实验结果表明,采用阶段升温方式明显缩短了干燥时间,且脱水率同样达到较高水平、外观形态和力学性能与采用传统方式所得样...     

Characteristics of the combustion water of organically bound tritium (OBT) measurements of fish samples

Improving accuracy and precision of measurements of organically bound tritium (OBT) activity concentration in environmental samples has become a key aspect of the study of radiological effects by scientists and regulators. Significant quenching effects are known to occur in the measurement of fish samples for OBT using a liquid scintillation counter. In this study, the quench effects of fish and vegetable samples were investigated, as well as the ionic composition of the samples following combustion, neutralization and distillation processes. Furthermore, revised water equivalent factors of various foodstuffs for OBT measurement were calculated using the Health Canada database.

     

Tritium content as indicator of environmental character on Taiwan Island

Environmental characters have been established by tritium contents in well water, coastal seawater and reservoir water collected from various places around Taiwan island. Tritium concentrations of samples were detected by a liquid scintillation analyzer TRI-CARB-LSC 2550 TR mode, with a low level standard quench curve. After samples were concentrated by electrolysis, tritium concentration was detected in optimum conditions of LLLSA. An electrolytic enrichment technique was also developed with a eurrent density of 100 mA/cm² and 0.4–0.6% (Na₂O₂) electrolyte in concentrated samples. Data observed show a lower tritium concentration for coastal seawater than for wells in the same area. The tritium concentration ratio of well and coastal seawater on the western side of Taiwan is 4.000 and on the eastern side 5.801. Tritium content of reservoir water is related to the logarithm of effective volume capacity.     

Uptake study of tritiated water (HTO) by plants after long-term continuous normal release around Narora Atomic Power Station

Knowledge of the dynamics of HTO in leafy plant–soil system is required to verify models, such as the NORMTRI code, which predict environmental tritium following its release. Tritium concentrations in plants has been evaluated using the code NORMTRI and experimentally by collection of samples of different plants and their soils samples. In the present study, major seasonal crop plants i.e. wheat, mustard, sugar cane, coriander, spinach, potato, were collected beyond Narora Atomic Power Station site boundary and gular, arandi, neem, ashok, amaltas, csuarina leaf samples within NAPS site boundary for analysis of HTO content. Data analysis indicated that HTO in leaf is strongly influenced by atmospheric relative humidity and type of the plant.     

Tritium in foods

The qualities of selected scintillation systems for the measurement of very low tritium content in water samples from foods were investigated in the liquid scintillation spectrometer. The influence of the parameters of the measuring method on the detection limit was defined by figures of merit. Optimum values were obtained with an emulsion system, which consists of PPO, bis-MSB, p-xylene and Triton N-101, and which takes up 40% water. 0.16 to 0.18 pCi/ml water are detectable with this system. Reference water, which is poor in tritium, was produced by combustion of propane.     

Variation of tritium concentration in the course of the degradation of fresh pine needles on a forest floor

Variation of tritium concentration was examined for 100 days in the course of degradation of fresh pine needles, which were left on a pine forest floor. No difference was observed on free water tritium (FWT) and organically bound tritium (OBT) concentrations of sterilized samples by gamma-ray irradiation or fumigation and control samples, attributable to incomplete sterilization. The OBT concentrations did not increase within the experimental period as the level of humus collected from the forest floor. The results suggest that a longer degradation time, more than 100 days, is necessary to elevate OBT up to the level, which is observed in the general environment.     

Changes in Physicochemical Properties and Volatile Compounds of Roselle (Hibiscus sabdariffa L.) Calyx during Different Drying Methods

Fresh roselle are high in moisture and deteriorate easily, which makes drying important for extending shelf-life and increasing availability. This study investigated the influence of different drying methods (oven-drying, freeze-drying, vacuum-drying, and sun-drying) on the quality of roselle calyx expressed as physicochemical properties (moisture content, water activity, soluble solids, color), volatile compounds, and microstructure. Oven-drying and freeze-drying reduced moisture content most while vacuum-drying and sun-drying were not as efficient. All drying methods except sun-drying resulted in water activities low enough to ensure safety and quality. Vacuum-drying had no impact on color of the dry calyx and only small impact on color of water extract of calyx. Drying reduced terpenes, aldehydes, and esters but increased furans. This is expected to reduce fruity, floral, spicy, and green odors and increase caramel-like aroma. Sun-drying produced more ketones, alcohols, and esters. Scanning electron microscopy revealed that freeze-drying preserved the cell structure better, and freeze-dried samples resembled fresh samples most compared to other drying techniques. The study concludes that freeze-drying should be considered as a suitable drying method, especially with respect to preservation of structure.     

Enrichment reliability of solid polymer electrolysis for tritium water analysis

We have developed a novel advanced enrichment apparatus for environmental tritium analysis called SPET (Solid Polymer Electrolysis for Tritium Water). It generates no explosive gas, requires no aqueous electrolyte, terminates enrichment rapidly, and the volume reduction is infinite. It has an automatic shutdown system which gives uniform conditions on every run, making the handling and determination of tritium concentrations very easy. The reliability of SPET was studied using environmental concentration standard water and the reproducibility error was found to be within 4%, which is sufficient for environmental measurements.