Activity Concentrations In Samples Research Articles

Investigation on atmospheric radioactivity sample association using consistency with isotopic ratio decay over time at IMS radionuclide stations

For the enhancement of the International Data Centre's products, specifically the Standard Screened Radionuclide Event Bulletin, an important step is to establish methods to associate the detections of the Comprehensive Nuclear-Test-Ban Treaty-relevant nuclides in different atmospheric radioactivity samples with the same radionuclide release to characterize its source for the purpose of nuclear explosion monitoring. Episodes of anomalously high activity concentrations in samples at the International Monitoring System radionuclide stations are used as the primary assumption for being related to the same release. For multiple isotope observations, the consistency of their isotopic ratios in subsequent samples with radioactive decay is another plausible hint for one unique release. The radioxenon observations that are associated with the nuclear test announced by the Democratic People's Republic of Korea in 2013 serve as case study to demonstrate the effectiveness of this basic approach and how the additionally associated samples improve the source location. We use two distinct puff releases, both of short duration, for the atmospheric transport modelling simulations to gain further evidence and confidence in our sample association study by identifying the air masses that link the releases to multiple samples. This basic approach will support the definition of analysis procedures and criteria for automatic sample association to be implemented in the Standard Screened Radionuclide Event Bulletin, which is of relevance for an expert technical analysis.

Distributions of fallout 137Cs, 239+240Pu and 241Am in a soil core from South Central China

The source and vertical distribution of 137Cs,239+240Pu and 241Am activity concentrations in a soil core from Hunan Province, China were investigated. The maximum 137Cs and 239+240Pu activity concentrations were 15.45 ± 0.76 mBq/g and 0.819 ± 0.066 mBq/g, respectively. While the maximum 241Am activity concentration in samples obtained from the core was 0.341 ± 0.019 mBq/g. The 240Pu/239Pu atom ratio and the 137Cs/239+240Pu activity ratio were 0.183 ± 0.011 and 19.5 ± 1.8, respectively, and both were consistent with the characteristic value of global fallout. The integrated 241Am/239+240Pu activity ratio for global fallout was also re-estimated. The measured 241Am/239+240Pu activity ratio (average 0.43 ± 0.07) in the samples was very close to the estimated value (0.45), which suggested their 241Am also came from the global fallout. Regarding the vertical distribution of 137Cs, 239+240Pu and 241Am in these red soil samples, all these radionuclides had higher concentrations in upper layers of several centimeters of soil while they had slightly lower concentrations in lower soil layers down to 30 cm. Vertical distributions of 137Cs/239+240Pu and 241Am/239+240Pu activity ratios indicated the migration velocity was Am ≈ Pu > Cs. The intrinsic chemical properties of the radionuclides as well as soil type and properties (acidic, nutrient-deficient and low in organic matter and cation exchange capacity) might be reasons for the differences in their migration behaviors.

A comparison of alpha-particle and gamma-ray spectrometry methods for determination of 235U, 238U and 226Ra activity concentration in samples of coal, slag and fly-ash

In order to compare alpha-particle and gamma-ray spectrometry, the activity concentrations of 235U, 238U and 226Ra in samples of coal, slag and fly-ash from the thermal power plant “Nikola Tesla A”, Serbia, were determined by these two methods. Methods were compared and discussed from the point of view of its precision, difficulty to apply and complexity. Gamma-ray spectrometry was performed with HPGe (High Purity Germanium) spectrometer, while alpha activity was measured by PIPS (Passivated Implanted Planar Silicon) detector. For the alpha-particle spectrometry, the chemical procedures applied were chromatographic resin extraction for uranium isotopes and micro-coprecipitation for 226Ra. Thin alpha sources were prepared by electrodeposition and filtration through polypropylene membrane filter for uranium determination, while filtration technique was performed for radium sources. For the evaluation of the statistical difference between individual measurement results obtained by application of two methods Z - test was used. In order to evaluate the difference between two methods used, paired samples t-test and F-test were applied. Results show that there is no statistical difference between two methods used and that gamma-ray spectrometry is a valid alternative to time consuming alpha spectrometry.

Assessment of the tritium distribution in the vegetation cover in the areas of underground nuclear explosions at the Semipalatinsk test site

This paper provides results of assessment of the tritium distribution in the vegetation cover in the areas of underground nuclear explosions at the Semipalatinsk Test Site (STS). The research was conducted at the former “Degelen” test site along the streams that are one of the main channels of tritium migration from underground nuclear explosions epicenters. The dominant plant species Carex supine and Achnatherum splendens that belong to different ecological groups in relation to humidity were selected as representatives of the vegetation cover.The TFWT (tissue free water tritium) and OBT (organically bound tritium) activity concentrations in the vegetation cover were measurement. TFWT activity concentration in the samples of both plant species had high values with an average of up to 30 kBq kg−1. The OBT activity concentration was 1–2 orders of magnitude lower than the TFWT in all plant samples. The TFWT and OBT activity concentrations in vegetation samples are closely correlated (r = 0.75, p < 0.05). No statistically significant difference was found between the content of tritium in the samples of Carex supine and those of Achnatherum splendens taken at the same locations.OBT/HTO ratios for vegetation samples of both species were close to equilibrium ratio used in environmental transfer models. In some cases, OBT/HTO ratios were significantly lower than one, which indicates that simple environmental transfer models may not accurately predict the behavior of HTO and OBT in different environmental compartments.The average OBT/HTO ratio for soil samples (0.6 ± 0.1) close to the equilibrium value indicates the equilibrium condition at the research area.The obtained [OBT]plant/[OBT]soil ratios indicate that soil organic matter accumulates tritium from year to year. However, in some locations with high tritium contamination ratios [OBT]plant/[OBT]soil were more than one due to OBT activity in soils is almost the same as OBT activity in plants.It was found that the nature of the spatial distribution of tritium in the vegetation cover in the areas of underground nuclear explosions is complex, and obviously depends on the location of the tunnels in which nuclear tests were conducted, as well as on the peculiarities of the hydrological regime of underground and surface waters, which are the main channels of tritium migration in the research area. Thus, the vegetation cover reflects the spatial distribution of tritium contamination in the sites of underground nuclear explosions and can be used as an indicator of the radiation situation when monitoring radiation-hazardous areas.

Results of international comparison tests on determination of &lt;sup&gt;137&lt;/sup&gt;Cs activity concentration in soil samples

In 2016—2019, comparison tests of different methods for quantitative determination of the content of the technogenic radionuclide 137 Cs in soil samples were performed. Soil samples were collected from areas with high and low 137 Cs contamination in Belarus. The intercomparison was performed as a part of an ongoing Russian—Swedish—Belarusian cooperation on the assessment of radioactive contamination of the environment. Three laboratories of the regular participants in the project and three laboratories from other facilities participated in the intercomparison that was focused on the samples of cultivated soil from the Gomel region (the first stage of comparisons, 3 samples) and the Grodno region (the second stage of comparisons, 4 samples). Results on activity concentrations in the samples presented by the participants were in satisfactory agreement with each other. The maximum deviation from the average value, that had been calculated for each sample based on the individual results from all laboratories, was 14%. Stage-averaged deviations from the inter-laboratory mean did not exceed 10%. Results of the comparison tests should be taken into consideration when comparing or merging experimental data from different laboratories participating in the Russian—Swedish—Belarusian cooperation project.

Vertical distribution of &lt;sup&gt;137&lt;/sup&gt;Cs in soddy-podzolic sandy soil in grasslands and forests of the Bryansk region in 2015–2016

Vertical distribution of natural and man-made radionuclides in the soil profile is a decisive parameter when calculating the dose rate of gamma radiation in the air above the ground and the effective dose of external human exposure. The main purpose of this work was to determine vertical distribution of137Cs in soddy-podzolic sandy and sandy-loam soils in forests and grasslands in the south-western districts of the Bryansk region in the remote period after the Chernobyl accident. In 2015–2016, soil cores were sampled in 7 virgin meadows and 13 forested areas to a depth of 20 cm. The cores were cut into horizontal layers 2 cm thick. The137Cs activity in the samples was determined using a semiconductor gamma spectrometer. The activity concentration in samples of dry soil (n = 200) ranged from 6.35 Bq/kg to 83300 Bq/kg with an average of 4550 Bq/kg. In the meadows in three cases, the maximum activity concentration was determined in the uppermost layer. With increasing depth, the activity concentration decreased and reached a minimum in the deepest layers. A difference between the surface layer and the deepest layer was two to three orders of magnitude. The three other meadows showed a relatively uniform distribution of137Cs in the upper 4–6 cm, followed by a decrease in activity concentration with an increase in depth. In one meadow area, a peak of the137Cs activity was found at a depth of 4–6 cm. In the forest, the most typical (in 10 cases) was the presence of a pronounced maximum activity concentration of137Cs in the uppermost layer. The experimentally obtained values of the137Cs inventory in the upper 20 cm of soil at the surveyed sites ranged from 42 to 1940 kBq/m2. The values of137Cs inventory positively and statistically significantly correlated with officially established levels of137Cs surface ground contamination for the territory of nearby settlements. Vertical migration of137Cs in the soil in the surveyed areas was mainly limited to the upper 10 centimeters. The layer on average contained 94% of the total137Cs inventory. Less than 1% of the total137Cs inventory was found in the deepest soil layer sampled (18–20 cm). The obtained137Сs activity distributions were used to calculate kerma rate in the air at a height of 1 m above the ground at the surveyed sites. The air kerma rate ranged from 52 to 2240 nGy/h (on average, 807 nGy/h). The caesium-137 deposit in the upper 6 cm of soil determined about 95% and 90% of the air kerma rate in the forests and in meadows, respectively. Radioactive caesium, which migrated into the soil to a depth of more than 10–12 cm, gave a negligible contribution (less than 1%) to the gamma-radiation dose rate in the air. In practical terms, it indicates that the depth of soil sampling equal to 20 cm is currently quite sufficient to estimate the dose rate of gamma radiation in the air in virgin grasslands and in forests.

Measurement of radon gas activity concentrations in drinking water in the city center of Adıyaman, Turkey

In this study, 16 water samples collected from homes and the water tanks in various districts from two different natural water sources, supplying Adiyaman's domestic drinking water. Measurements of radon gas activity concentrations in collected samples have been performed by AlphaGUARD PQ2000 PRO radon detector. The average radon (222Rn) activity concentrations of samples taken from the natural water resources and homes were found to be 0.39 ± 0.11 and 0.51 ± 0.14 Bq/L, respectively. In addition, the annual effective dose equivalent that exposed due to radon gas in drinking water is also calculated and found to be 1.30 ± 0.36 μSv/y. The upper limit for radon gas activity concentrations in drinking waters has been defined by the United States Environmental Protection Agency (USEPA), United Nations Scientific Committee on the Effects of Atomic Radiation, and World Health Organization to be 11, 40, and 100 Bq/L, respectively. The measured values of radon gas activity concentrations are lower than that of limit value defined by the USEPA.

Radioactivity concentration variation with depth and assessment of workers' doses in selected mining sites

Mining workers are exposed to radiation in the process of extracting minerals from the earth crust. In this research, activity concentration of the radionuclides in samples collected at different depths in Komu (0–220 ft) and Olode (0–30 ft) mining sites, Oyo State, Nigeria and the associated workers' radiological risks were assessed. Gemstones from these sites are mined for local and international markets. The radionuclide contents of the samples were determined using Gamma spectroscopy technique. At Komu, 238U and 232Th concentrations, with few exceptions, increased with depth while that of 40K had no defined pattern. At Olode site, 238U and 232Th concentrations decreased with depth while that of 40K was almost constant. Internal hazard indices at Komu in some cases indicated an unacceptable level of risk to workers. Workers' doses would have been underestimated by between 12 and 55% if the activity concentrations of samples in the pit were not included in the calculation.

Modelling the transfer of 14C from the atmosphere to grass: A case study in a grass field near AREVA-NC La Hague

Radioactive 14C is formed as a by-product of nuclear power generation and from operation of nuclear fuel reprocessing plants like AREVA-NC La Hague (North France), which releases about 15 TBq per year of 14C into the atmosphere. Since the autumn of 2006, 14C activity concentrations in samples from the terrestrial environment (air, grass and soil) have been monitored monthly on grassland 2 km downwind of the reprocessing plant. The monitoring data provides an opportunity to validate radioecology models used to assess 14C transfer to grassland ecosystems. This article compares and discusses the ability of two different models to reproduce the observed temporal variability in grass 14C activity in the vicinity of AREVA-NC La Hague. These two models are the TOCATTA model which is specifically designed for modelling transfer of 14C and tritium in the terrestrial environment, and PaSim, a pasture model for simulating grassland carbon and nitrogen cycling. Both TOCATTA and PaSim tend to under-estimate the magnitude of observed peaks in grass 14C activity, although they reproduce the general trends. PaSim simulates 14C activities in substrate and structural pools of the plant. We define a mean turn-over time for 14C within the plant, which is based on both experimental data and the frequency of cuts. An adapted PaSim result is presented using the 15 and 20 day moving average results for the 14C activity in the substrate pool, which shows a good match to the observations. This model reduces the Root Mean Square Error (RMSE) by nearly 40% in comparison to TOCATTA.

Application of the Monte Carlo method for the efficiency calibration of CsI and NaI detectors for gamma-ray measurements from terrestrial samples

Gamma-ray measurements in terrestrial/environmental samples require the use of high efficient detectors because of the low level of the radionuclide activity concentrations in the samples; thus scintillators are suitable for this purpose. Two scintillation detectors were studied in this work; CsI(Tl) and NaI(Tl) with identical size for measurement of terrestrial samples for performance study. This work describes a Monte Carlo method for making the full-energy efficiency calibration curves for both detectors using gamma-ray energies associated with the decay of naturally occurring radionuclides (137)Cs (661keV), (40)K (1460keV), (238)U ((214)Bi, 1764keV) and (232)Th ((208)Tl, 2614keV), which are found in terrestrial samples. The magnitude of the coincidence summing effect occurring for the 2614keV emission of (208)Tl is assessed by simulation. The method provides an efficient tool to make the full-energy efficiency calibration curve for scintillation detectors for any samples geometry and volume in order to determine accurate activity concentrations in terrestrial samples.

Transfer of natural and man made radionuclides from plants to roe deer and farm animals

In this work the transfer behavior of long living radionuclides from the Thorium decay series (Ra-228, Th-228, Th-232) as well as of K-40 and Cs-137 is studied. In a small area of middle Europe (southeast Gemany) showing an increased Thorium content of soil the activity concentrations in samples of feed plants, farm animals, farm animal products, roe deer has been determined. The concentration ratios feed-to-animal tissue and to animal products are calculated indicating a significantly enhanced transfer from feed to roe deer tissues. Determinations of the activity concentrations in fish (carp), pig (tissues), egg, milk complete this examinations. Among all studied samples which are important for human nourishing eggs and carp cause the greatest exposure by ingestion.