Liquid Scintillation Counting Techniques Research Articles

Estimation of Radionuclide Concentrations and Average Annual Committed Effective Dose due to Ingestion for the Population in the Red River Delta, Vietnam

Radioactivity concentrations of nuclides of the 232Th and 238U radioactive chains and 40K, 90Sr, 137Cs, and 239+240Pu were surveyed for raw and cooked food of the population in the Red River delta region, Vietnam, using α-, γ-spectrometry, and liquid scintillation counting techniques. The concentration of 40K in the cooked food was the highest compared to those of other radionuclides ranging from (23 ± 5) (rice) to (347 ± 50) Bq kg−1 dw (tofu). The 210Po concentration in the cooked food ranged from its limit of detection (LOD) of 5 mBq kg−1 dw (rice) to (4.0 ± 1.6) Bq kg−1 dw (marine bivalves). The concentrations of other nuclides of the 232Th and 238U chains in the food were low, ranging from LOD of 0.02 Bq kg−1 dw to (1.1 ± 0.3) Bq kg−1 dw. The activity concentrations of 90Sr, 137Cs, and 239+240Pu in the food were minor compared to that of the natural radionuclides. The average annual committed effective dose to adults in the study region was estimated and it ranged from 0.24 to 0.42 mSv a−1 with an average of 0.32 mSv a−1, out of which rice, leafy vegetable, and tofu contributed up to 16.2%, 24.4%, and 21.3%, respectively. The committed effective doses to adults due to ingestion of regular diet in the Red River delta region, Vietnam are within the range determined in other countries worldwide. This finding suggests that Vietnamese food is safe for human consumption with respect to radiation exposure.

Accurate Quantification of Radiosulfur in Chemically Complex Atmospheric Samples.

An ultralow-level liquid scintillation counting (LSC) technique has been used in measuring radiosulfur (cosmogenic 35S) in natural samples. The ideal half-life of 35S (∼87 days) renders it a new way to examine various biogeochemical problems. A major limitation of the technique is that complex chemical compositions in atmospheric samples may lead to color quenching of LSC cocktails, a serious problem prolonging the pretreatment time (>1 week) and hampering the accurate determination of 35S. For application of the technique where many of the most important atmospheric chemical processes are examined, significant interferences arise and accurate analysis in small samples is not possible. In this study, we optimized the LSC method to minimize/eliminate color quenching in high-sensitivity 35S measurements. The analytical performance of this new method was evaluated using control laboratory experiments and natural aerosol samples. Results show that the new method offers comparable accuracy as the traditional method for normal environmental samples [bias: <±0.03 disintegrations per minute (DPM)] and significantly shortens the pretreatment time to less than 3 days. For samples that were heavily contaminated by color-quenching agents, the accuracy of this new method is notably higher than that of the traditional method (maximum bias: -0.3 vs -1.5 DPM). With the growing use of radiosulfur in the field of Earth and planetary sciences, the accurate determination of 35S would provide a reliable field-based constraint for modeling 35S production in the atmosphere and allow a wide range of atmospheric, hydrological, and biogeochemical applications.

Rapid analysis method for the determination of 14C specific activity in irradiated graphite.

14C is one of the limiting radionuclides used in the categorization of radioactive graphite waste; this categorization is crucial in selecting the appropriate graphite treatment/disposal method. We propose a rapid analysis method for 14C specific activity determination in small graphite samples in the 1–100 μg range. The method applies an oxidation procedure to the sample, which extracts 14C from the different carbonaceous matrices in a controlled manner. Because this method enables fast online measurement and 14C specific activity evaluation, it can be especially useful for characterizing 14C in irradiated graphite when dismantling graphite moderator and reflector parts, or when sorting radioactive graphite waste from decommissioned nuclear power plants. The proposed rapid method is based on graphite combustion and the subsequent measurement of both CO2 and 14C, using a commercial elemental analyser and the semiconductor detector, respectively. The method was verified using the liquid scintillation counting (LSC) technique. The uncertainty of this rapid method is within the acceptable range for radioactive waste characterization purposes. The 14C specific activity determination procedure proposed in this study takes approximately ten minutes, comparing favorably to the more complicated and time consuming LSC method. This method can be potentially used to radiologically characterize radioactive waste or used in biomedical applications when dealing with the specific activity determination of 14C in the sample.

The distribution of tritium in aquatic environments, Lithuania

The aim of this study is to investigate mobile radionuclide tritium (3H or T) activity dynamics in aquatic environments related to Ignalina NPP (INPP) site and water bodies located in remote areas unaffected by the INPP. The 3H excess in the INPP environment was analyzed and compared to the variable 3H background level over the period of operation of the INPP (end of 1983 – end of 2009) and during the initial stage of decommissioning (2010–2017). 3H in the INPP vicinity has been studied in the water of artificial channels related to operation of the INPP and site drainage, in natural surface water bodies and, at a smaller scale, in unconfined groundwater. This study presents an extensive 3H data set extending back to 1980, i.e. before INPP operation started. To assess the contribution of global sources to 3H dynamics, monthly precipitation was also studied, along with water from the Baltic Sea, Curonian Lagoon and Nemunas River were studied as well, all three of these located in the Lithuanian maritime zone. The 3H activity concentration in water was measured using liquid scintillation counting (LSC) techniques (direct counting and counting after enrichment). During the period of INPP operation, 3H from liquid effluent could be clearly observed in discharge channels, occurring in rather low diluted conditions, as well as in Lake Druksiai, the cooling basin, at an even more diluted level. The highest 3H activity concentration in Lake Druksiai was observed in 2003 and reached 201.3 ± 1.3 TU at a time when 3H activity concentrations in background water bodies was 9.2 ± 3.5 TU. After the closure of the INPP, the 3H liquid effluent rate reduced by approximately two orders of magnitude (from 1012 Bq in 1991 to 1010 Bq in 2016) and when decommissioning activity commenced then the 3H activity concentration fell to that approaching the background level (19–27 TU) that can still be observed in industrial discharge and rainwater drainage channels. 3H as a result of leakage from the INPP can be observed in groundwater only in direct proximity to the INPP site near the radioactive waste storage zone.

Standardisation and half-life of 89Zr

The nuclide 89Zr is being tested for the labelling of compounds with long blood circulation times. It decays by beta plus emission (22.8%) and by electron capture (77.2%) to 89Y. Its half-life has been determined by following the decay rate with two measurement systems; an Ionisation Chamber and an HPGe detector. The combination of six results gives a value of T1/2 = 78.333 (38) h, slightly lower than the DDEP recommended value of 78.42 (13) h. This radionuclide has also been standardised by liquid scintillation counting, 4πγ counting and coincidence techniques.

Optimization of the liquid scintillation counting technique for the European interlaboratory comparison on gross α/β activity concentrations in water

A liquid scintillation counting (LSC) measurement method optimization for the gross α/β activity analysis in drinking waters with different chemical and radionuclide composition was performed. The optimized method was suitable to provide gross radioactivity results in drinking waters with the levels of the accuracy and precision similar to those obtained using other radioactivity screening techniques. Robust LSC results contributed to the calculation of gross α/β activity reference values of EC-JRC interlaboratory comparison water samples in 2012. Some of the most common errors in the determination of the gross radioactivity using the LSC are presented.

Absolute standardizations of 99mTc and 57Co by 4π electron-gamma liquid scintillation coincidence counting for SIRTI and SIR comparisons

The radionuclides 99mTc and 57Co were standardized via absolute liquid scintillation counting techniques. We provide the first technical report on the absolute standardization of 99mTc using 4π(LS)e-γ coincidence counting. The low detection efficiency of low-energy conversion electrons translates into a large efficiency extrapolation range. A simulation indicated that the γ-ray interacting with the liquid scintillator introduces curvature to the count rate vs. efficiency relationship, the approximation of the functional form used for extrapolation providing the main measurement uncertainty for 99mTc. A detection efficiency analysis for both radionuclides is presented. Results from the standardizations, and SIRTI and SIR comparison exercises are reported.

Comparison of radon (Rn-222) concentration in Portugal and Finland underground waters

Intercomparison results of Radon (Rn-222) measurements using two phase liquid scintillation counting (LSC) technique was performed. The results obtained are in good agreement with the assigned levels. Several water samples from different Portuguese underground catchments were also analyzed. In general, the waters showed acceptable Rn-222 levels, however, 20% presented concentrations between 500 and 1000 Bq L−1 and 5% higher than 1000 Bq L−1. In Finland, the mean Rn-222 concentration obtained in drilled wells was 460 Bq L−1 and in wells dug in soil 50 Bq L−1. Approximately 10% of drilled wells exceeded a radon concentration of 1000 Bq L−1.

Biogenic fraction determination in fuels – Optimal parameters survey

The novel method for biogenic component determination in liquid fuels by direct measurement of the 14C activity concentration via liquid scintillation counting (LSC) technique has been used in few laboratories worldwide. This paper presents results of the development of method for bio-component quantification in fuel mixtures in the Nuclear Physics Laboratory Novi Sad, Serbia, as well as their comparison to established methodology in literature with intent to define optimal parameters and measurement conditions for 14C determination in biofuels. Therefore, the purpose of the paper is to give comprehensive overview of optimal parameters such as scintillation cocktail and vial selection, fuel/cocktail ratio and best calibration procedure of liquid scintillation counter Quantulus 1220™, with practical information for laboratories that intend to develop this technique. Biodiesel produced from two different feedstock materials was mixed with two commercial fossil matrices to produce fuel blends containing 1–100% FAME (Fatty Acid Methyl Esters), which were analyzed for calibration purposes. Analytical study of relation between the detected released energy and quench level led to establishment of calibration curves specific to the fuel types produced in this moment on the market in Serbia.

Radioecological investigation of 3H, 14C, and 129I in natural waters from Fuhrberger Feld catchment, Northern Germany

Ongoing radionuclide releases from nuclear facilities, e.g. from reprocessing plants, but also from nuclear reactors require monitoring of the environment. Particularly drinking water reservoirs are prone to possible radionuclide accumulation fostering the need for routine surveillance. In this work, we investigated tritium (3H), radiocarbon (14C), and iodine-129 (129I) activity levels in natural aquatic samples at the water protection area of Fuhrberger Feld near Hannover city, Northern Germany. For that aim, a low-level liquid scintillation counting (LSC) technique was used to measure 3H in the water samples based on a distillation process after alkaline permanganate treatment. Isotopic ratios for both 14C and 129I were measured by accelerator mass spectrometry (AMS) after chemical separation and purification of the samples. Mean 3H levels in precipitation (8.8 ± 3.4 TU) were found to be comparable to its levels in precipitation data in Germany. Rivers and small streams revealed similar mean 3H value (11.0 ± 3.3 TU) as in lake water (10.6 ± 3.4 TU). Variations in 3H concentrations in groundwater samples were observed and discussed. 14C levels in all groundwater samples were below the atmospheric natural level of 100 pMC indicating no anthropogenic input of radiocarbon. The 129I/127I isotopic ratios in all investigated water samples were in the order of 10−8 to 10−7, which is significantly higher than the pre-nuclear natural equilibrium isotopic ratio (∼1.5 × 10−12). In strong contrast to all other regional groundwaters, the Fuhrberger Feld groundwater has much higher values of 129I concentration and 129I/127I isotopic ratio close to the ones of surface water. The overall annual effective dose via ingestion for all nuclides in the investigated groundwater remains substantially below the reference dose level of 0.1 mSv a−1.

Release behavior of tritium in pure copper and its alloys into pure water at ambient temperature

Release behaviors of tritium (T) from pure copper (Cu) and its alloys into pure water were examined at ambient temperature by a tritium imaging plate technique and a liquid scintillation counting technique. Two mechanisms govern the liberation of T into pure water; one is rapid release and the other is chronic release. The former is caused by diffusional release of T dissolved in bulk of Cu alloys and the latter by release of T strongly bound on/in surface oxide layers.

Standardisation and precise determination of the half-life of 44Sc

The half-life of the positron-emitter 44Sc has been determined by following the decay rate with two measurement systems; an Ionisation Chamber and a HPGe detector. The combination of seven results gives a value of T1/2=4.042 (25)h, about 2% higher than the recommended value of T1/2=3.97 (4)h (Browne, 2011) and with a lower uncertainty. This radionuclide has also been standardised by coincidence counting, and liquid scintillation counting techniques. A 44Ti/44Sc generator developed at CIEMAT was used to obtain the 44Sc solutions used in all measurements.

Analytical Method for Measuring Cosmogenic (35)S in Natural Waters.

Cosmogenic sulfur-35 in water as dissolved sulfate ((35)SO4) has successfully been used as an intrinsic hydrologic tracer in low-SO4, high-elevation basins. Its application in environmental waters containing high SO4 concentrations has been limited because only small amounts of SO4 can be analyzed using current liquid scintillation counting (LSC) techniques. We present a new analytical method for analyzing large amounts of BaSO4 for (35)S. We quantify efficiency gains when suspending BaSO4 precipitate in Inta-Gel Plus cocktail, purify BaSO4 precipitate to remove dissolved organic matter, mitigate interference of radium-226 and its daughter products by selection of high purity barium chloride, and optimize LSC counting parameters for (35)S determination in larger masses of BaSO4. Using this improved procedure, we achieved counting efficiencies that are comparable to published LSC techniques despite a 10-fold increase in the SO4 sample load. (35)SO4 was successfully measured in high SO4 surface waters and groundwaters containing low ratios of (35)S activity to SO4 mass demonstrating that this new analytical method expands the analytical range of (35)SO4 and broadens the utility of (35)SO4 as an intrinsic tracer in hydrologic settings.

The importance of the beta spectrum calculation for accurate activity determination of 63Ni by means of liquid scintillation counting

The activity concentration of a 63Ni solution was determined by means of two liquid scintillation counting techniques: the TDCR method and the CIEMAT/NIST efficiency tracing technique. The results of both methods are in excellent agreement, provided that the 63Ni beta spectrum calculation accounts for the atomic exchange effect. Thus, new beta spectrum calculations resolve a discrepancy that has been found in previous analyses. The influence of the computed beta spectrum on the final uncertainty of the activity concentration is discussed.

Improvement of measuring methods and instrumentation concerning 222Rn determination in drinking waters – RAD7 and LSC technique comparison

A procedure for the determination of 222Rn in environmental water samples using liquid scintillation counting (LSC) was applied and optimized. A minimum detectable activity of 0.029Bql−1 in a 20ml glass vial (10ml water sample mixed with 10ml of liquid scintillation cocktail) has been achieved during 300min of measurement time. The procedure was compared with RAD7 radon detector measurements. 226Ra content in the water was determined by gamma-ray spectroscopy. Applications to drinking waters collected from public drinking fountains in the Vojvodina (Serbia) are presented with annual effective dose for ingestion and inhalation for adults calculated.

Standardisation of 223Ra by liquid scintillation counting techniques and comparison with secondary measurements

An aqueous solution of 223Ra chloride in equilibrium with its decay progeny was standardised by liquid scintillation counting techniques. Since secular equilibrium with the decay progeny of 223Ra had been established by the time of measurement, the apparent detection efficiency of 223Ra was approximately 6 and was determined by both the CIEMAT/NIST efficiency tracing technique and the 4π(LS)-γ digital coincidence counting techniques. The results obtained were compared with γ-spectrometry and ionisation chamber measurements. Whilst the γ-spectrometry measurements were in agreement (albeit exhibiting a large spread (18%) in the individual activity estimations using the main γ-emissions), a significant discrepancy of the order of 9% was identified between the liquid scintillation counting results and those obtained using published calibration factors for a variety of radionuclide calibrators.

Radiochemical methodologies applied to determination of zirconium isotopes in low-level waste samples from nuclear power plants

The 93Zr determination in low-level radioactive wastes generated at nuclear power plants is an important issue for waste disposal purpose. This paper describes an analytical methodology developed for 93Zr determination based on selective separation using extractive resins associated with inductively coupled plasma mass spectrometry (ICP-MS) and liquid scintillation counting (LSC) measurements. The 93Zr results obtained for waste samples were in a good agreement for both techniques and the detection limits of 0.045 μg L−1 and 0.05 Bq L−1 were obtained for ICP-MS and LSC techniques respectively.

Depletion of eugenol residues from the skin-on fillet tissue of rainbow trout exposed to 14C-labeled eugenol

Abstract The U.S. is lagging in access to an approved immediate-release sedative, i.e. a compound that can be safely and effectively used to sedate fish and has no withdrawal period. AQUI-S® 20E (10% active ingredient, eugenol) is under investigation as an immediate-release sedative for freshwater finfish. Because of its investigational status, data are needed to characterize the depletion, distribution, and identity of AQUI-S® 20E residues in fillet tissue. Rainbow trout (Oncorhynchus mykiss) were exposed to uniformly ring labeled 14C-eugenol at a nominal concentration of 10 mg/L for 60 min in 18 °C water. Fish (n = 6) were sampled immediately after the exposure (0 min) then at 30, 60, 120, and 240 min. Eugenol concentrations and characterization of 14C residues in the fillet tissue were determined by high pressure liquid chromatography and flow-through liquid scintillation counting techniques. Total 14C-residue burdens in fillet tissue were determined by tissue oxidation and static liquid scintillation counting techniques. Maximum eugenol and 14C-eugenol equivalent residue concentrations in the fillet tissue were measured immediately after the exposure (44.5 and 38.8 μg/g, respectively). Eugenol was the primary 14C-residue (> 90% of all 14C-residues) in extracts from fillet tissue taken from fish sampled immediately after the exposure (0 min) and from fish sampled at 30 and 60 min after the exposure. The depletion of 14C-eugenol residues from the fillet tissue was rapid (t1/2 = 26.25 min) after transferring the exposed fish to fresh flowing water.

A simple-rapid method to separate uranium, thorium, and protactinium for U-series age-dating of materials

Uranium-series dating techniques require the isolation of radionuclides in high yields and in fractions free of impurities. Within this context, we describe a novel-rapid method for the separation and purification of U, Th, and Pa. The method takes advantage of differences in the chemistry of U, Th, and Pa, utilizing a commercially-available extraction chromatographic resin (TEVA) and standard reagents. The elution behavior of U, Th, and Pa were optimized using liquid scintillation counting techniques and fractional purity was evaluated by alpha-spectrometry. The overall method was further assessed by isotope dilution alpha-spectrometry for the preliminary age determination of an ancient carbonate sample obtained from the Lake Bonneville site in western Utah (United States). Preliminary evaluations of the method produced elemental purity of greater than 99.99% and radiochemical recoveries exceeding 90% for U and Th and 85% for Pa. Excellent purity and yields (76% for U, 96% for Th and 55% for Pa) were also obtained for the analysis of the carbonate samples and the preliminary Pa and Th ages of about 39,000 years before present are consistent with 14C-derived age of the material.

Determination of selected natural radionuclide concentrations in southwestern Caspian groundwater using liquid scintillation counting

Twenty-seven spring water samples from southwestern shore of the Caspian Sea were analysed for their contents of gross alpha and beta, ²²²Rn, ²²⁶Ra and total uranium using a liquid scintillation counter (LSC). Other methods such as the Environmental Protection Agency (EPA) method 900 for gross alpha/beta measurement, radon emanation for ²²⁶Ra determination and laser fluorimetry for total uranium content were applied to make a comparison with the LSC technique. The levels of measured ²²²Rn and ²²⁶Ra range from 0.5 to 54 Bq l⁻¹ and from 14 to 297 mBq l⁻¹, respectively. The levels of gross alpha and beta are from 16 mBq l⁻¹ to 1.0 Bq l⁻¹ and from 22 to 630 mBq l⁻¹, respectively. The total uranium contents are from 3 to 66 mBq l⁻¹. It has been shown that the simple liquid scintillation counting technique could be applied conveniently for such studies where analysis of numerous samples is concerned.