Universal calibration of a scintillation spectrometer with a NaI(Tl) detector when measuring 137Cs activity in counting samples of arbitrary density and volume

The article proposes an empirical method for constructing a universal calibration for a scintillation gamma spectrometer, which allows determining the activity and specific activity of 137Cs with an accuracy of no more than 15% in counting samples of arbitrary density and volume in cylindrical containers with a volume of 250 ml and 500 ml. To construct calibration ratios, measurements of 137Cs sample media prepared on the basis of materials of different densities (quartz sand, plastic granules and sawdust) were performed. The calibration was carried out by preparing samples from the listed materials with a volume of 50 to 250 ml in increments of 50 ml for a 250 ml container and 100-500 ml in increments of 100 ml for a 500 ml container. Along with taking into account the volume of the counting sample, its weighing was also carried out. The result of the measurements performed for each material was the ratio of the activity of the counting sample to the counting intensity in the 137Cs window, depending on the volume. The universal calibration factor is obtained by taking into account the counting rate from the mass and volume of the sample for the corresponding measuring vessel.

Sediment Assessment of the Pchelina Reservoir, Bulgaria

The temporal dynamics of anthropogenic impacts on the Pchelina Reservoir is assessed based on chemical element analysis of three sediment cores at a depth of about 100–130 cm below the surface water. The 137Cs activity is measured to identify the layers corresponding to the 1986 Chernobyl accident. The obtained dating of sediment cores gives an average sedimentation rate of 0.44 cm/year in the Pchelina Reservoir. The elements’ depth profiles (Ti, Mn, Fe, Zn, Cr, Ni, Cu, Mo, Sn, Sb, Pb, Co, Cd, Ce, Tl, Bi, Gd, La, Th and Unat) outline the Struma River as the main anthropogenic source for Pchelina Reservoir sediments. The principal component analysis reveals two groups of chemical elements connected with the anthropogenic impacts. The first group of chemical elements (Mn, Fe, Cr, Ni, Cu, Mo, Sn, Sb and Co) has increasing time trends in the Struma sediment core and no trend or decreasing ones at the Pchelina sampling core. The behavior of these elements is determined by the change of the profile of the industry in the Pernik town during the 1990s. The second group of elements (Zn, Pb, Cd, Bi and Unat) has increasing time trends in Struma and Pchelina sediment cores. The increased concentrations of these elements during the whole investigated period have led to moderate enrichments for Pb and Unat, and significant enrichments for Zn and Cd at the Pchelina sampling site. The moderately contaminated, according to the geoaccumulation indexes, Pchelina Reservoir surface sediment samples have low ecotoxicity.

INITIAL EVALUATIONS OF NATURAL ( 226Ra, 232Th and 40K) AND ARTIFICIAL ( 137Cs) RADIOACTIVITY OF ESKIKÖY MINERALIZATION AREA (GÜMÜŞHANE, TÜRKIYE)

Within the scope of this study, the natural (226Ra, 232Th and 40K) and artificial (137Cs) radioactivity concentrations of the Eskiköy Mine area within the borders of Gümüşhane, which is located in an important metallogenic belt of Turkey, were investigated. In order to determine the natural and artificial radioactivity of the field soils developed due to mineralization, hydrothermal alteration and weathering, 12 soil samples were taken and activity concentrations of 232Th, 226Ra, 40K and 137Cs radio isotopes were measured with a gamma detector. It was observed that the 40K natural radio isotope activities of the area mostly exceeded the weighted world average, and the 232Th, and 226Ra natural radio isotope activities exceeded the weighted world averages at 5 of the 12 sampling points. It was determined that the artificial 137Cs activity concentrations in the area were above the detection limit at 9 sampling points and above 3 Bq/kg at 8 sampling points. It has been evaluated that the high 137Cs activities detected in the Eskiköy mine area are due to the Chernobyl nuclear power plant accident and similar anthropogenic effects. The mine area was also evaluated in terms of radiation risk in the context of medical geology, with parameters of radiological hazard indices, radium conjugate activity value, absorbed dose rate and annual effective dose rate, and remarkable findings were obtained. When all these findings of the study area are evaluated together, it has been concluded that the Eskiköy mining area should be studied in more detail in terms of natural and artificial radioisotope activity concentrations and their effects on human health.

TRANSFORMATION OF RADIOCESIUM SPECIATION IN PONDS AT THE VICINITY OF FUKUSHIMA DAI-ICHI NUCLEAR POWER PLANT AND ITS DYNAMICS IN “SEDIMENTS-WATER” SYSTEM

The paper is concerned with the results of 137Cs monitoring in the irrigation ponds of the Okuma town in the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) exclusion zone. The 137Cs activity concentrations in the ponds appeared to be higher than those in the rivers and dam reservoirs in the region. The study has revealed a trend for a decline in 137Cs activity concentrations, both particulate and dissolved. The rate of particulate 137Cs decline was much higher than that of dissolved. The total distri- bution coefficient Kd (137Cs) in the suspended sediment-water system in the studied ponds was decreasing in time with the rate constant of 0.12-0.18 year-1. Assuming that the decrease in Kd is associated with decomposition of hot glassy particles, the time scale of 137Cs leaching from them in these water bodies was estimated to be 5-8 years. These estimates are consistent with the findings of recent laboratory experiments on the subject. With respect to seasonal variations, the highest levels of dissolved 137Cs in the studied ponds were observed from June to October as a function of specific pond and monitoring year. Based on data about 137Cs speciation in the bottom sediment top layer of the ponds and its distri- bution in the sediment-water system, the exchangeable radiocesium interception potential RIPex(K) for the ponds sediments was estimated to be 1650-2250 mg-eq/kg, which is within the range of values measured by laboratory studies.

Characterization of radionuclides in the marine sediments of Orca Seamount, Admiralty Bay, and Mackellar Cove

Contamination by radioactive elements and their transfer through the trophic chain can have harmful effects on ecosystems and human health, therefore its continuous monitoring is important. The present study aimed to characterize the concentration of radionuclides of natural and anthropogenic origin in marine sediments from three areas in the northwest of Antarctica, Orca Seamount, Admiralty Bay and Mackellar Inlet, in order to evaluate possible risk levels, sources and transportation routes. Measurements were made using a high-resolution Canberra spectrometer and methodological precision and accuracy was assessed by analyzing reference materials certified by the International Atomic Energy Agency (IAEA), SOIL-6 and Moss SOIL-447. The results showed a low concentration of 137Cs activity in the marine sediments, decreasing towards the deep zone, validating the atmospheric pathway as the main transport route for this radionuclide of anthropic origin. The activity concentration of radionuclides of natural origin 226Ra and 40K, confirm the volcanic origin of the region, corroborating the geological evolution stages of the sector, and the changes in the source of material to the mantle. The calculated radiation hazard indexes showed that current activity concentrations of radioactive elements do not pose a health risk. It is important in the future to improve the understanding of the relationship between hydrothermalism in the area and the activity concentration of radionuclides of natural origin.

Dating and interpretation of recent clastic sediments in an urban cave

Capshaw Cave functions as a major stormwater runoff channel for the city of Cookeville, Tennessee, receiving inputs from several large sinkholes. Sediments deposited in the cave reflect the history of erosion and runoff from the city as it grew over the last century. At various locations in the cave, ~1 m thick sequences of flood-deposited, laminated fine sediments were observed along the modern stream. Alternating laminations observed in the upper ~40 cm of the sediment profile varied between 0.5 cm thick (10Y 7/6 yellow, fine sand) and 2.0 cm thick (10Y 3/2 very dark grayish brown silty sand) layers. Based on measurements of 137Cs activity, the upper 35 cm of sediment was deposited between 1963 (the peak year of 137Cs fallout from nuclear testing) and 2013 (the year samples were collected), at an average rate of 0.7 cm/y. A total of 23 alternating pairs of layers indicate an average flood recurrence interval of ~2.2 years between 1963 and 2013. Total Pb concentrations measured in cave sediments showed a peak at the 45 cm depth, suggesting that sediments above this level were deposited after the decline in Pb emissions in the 1970s, and showing general agreement with the timing of deposition suggested by 137Cs. Below 40 cm, the dark silty sand layers were fewer in number and increased in thickness (up to 10 cm), possibly due to changes in cave hydrology or sediment erosion from the surrounding watershed. These findings suggest that, before the 1960s, sedimentation rates were higher and floods were less frequent. After the 1960s, sedimentation rates decreased and floods became more common, probably as a result of urbanization in the watershed.

Author Correction: A dataset of 137Cs activity concentration and inventory in forests contaminated by the Fukushima accident

A Correction to this paper has been published: https://doi.org/10.1038/s41597-021-00855-5.

Tritium activity concentration and behaviour in coastal regions of Fukushima in 2014

We observed 3H activity concentrations and the 137Cs activity concentrations during the SoSo 5 rivers cruise in 2014 and at the Tomioka port in 2014–2018. The 3H activity concentrations at coastal stations located close to the Fukushima coast ranged from 90 Bq m−3 to 175 Bq m−3, and decreased between 67 Bq m−3 to 83 Bq m−3 at the stations located 12–16 km from the coast. The 3H activity concentration at the estuaries and ports, except at 56 north canal of the FNPP1 site, are around 200–500 Bq m−3 and slightly lower than the 3H activity concentration of 500–600 Bq m−3 observed in the rivers. These gradients of the 3H activity concentrations in the coastal region might indicate the large effect of 3H flux through the rivers. On the other hand, the 3H activity concentration at 56N of the FNPP1 site was significantly high compared to the 3H activity concentration in surrounding waters both north and south of the FNPP1 site and in river waters. It should also be noted that the 3H activity concentrations were similar at the stations located both north and south of the FNPP1 site, while the 137Cs activity concentrations were lower at the stations north of the FNPP1 site and higher at the stations south of the FNPP1 site. This indicated that the major sources of 137Cs could be the FNPP1 site as the point source while the source of 3H should be more diffuse and linked to riverine inputs located north and south of the FNPP1 site. The 3H / 137Cs activity ratios in coastal waters were 1.2–2.2 as obtained via the slopes by standardised major axis regressions between the 3H activity concentration and the 137Cs activity concentration of SoSo samples and Tomioka Port observed in 2014–2018, which is significantly high compared to that of the released radionuclides derived from the FNPP1 site, which was 0.01 in 2011 just after the accident. The open-water 3H activity concentration contribution to coastal waters was estimated to be 67 ± 20 Bq m−3 and 66 ± 17 Bq m−3 as the intercepts also by standardised major axis regressions. These estimates are consistent with 50 Bq m−3 obtained at the Kuroshio region as the background levels of 3H activity concentration in open water. The 3H and 137Cs fluxes to the coastal region of Fukushima based on the open-water movement, freshwater flux from the rivers based on their respective catchment, and mean monthly precipitation were estimated. The largest 3H flux is the open-water inflow from the north of the FNPP1 site and it reaches 52 GBq day−1, while the rivers north of the FNPP1 site showed 3–5 GBq day−1 fluxes. We obtained a 3H flux as 1.9–4.5 GBq day−1 of 3H using the 3H activity concentration in the port, which is comparable with the fluxes obtained from the rivers located north of the FNPP1 site. While using 3H activity concentration at the 56 north canal of FNPP1, we obtained 28–86 GBq day−1 fluxes, which is one order of magnitude larger than those estimated using 3H activity concentration in the FNPP1 port. One of the reasons could be the very high variability of the 3H levels at 56 north canal and in the port of FNPP1, explaining variable 3H/137Cs activity ratio observed at 56 north canal and in the port of FNPP1. The 3H activity concentration of TFWT in the fish filets collected close to the FNPP1 site ranged from 97 ± 11 Bq m−3 to 144 ± 11 Bq m−3, which were similar to the 3H activity concentrations in the surrounding seawater, in agreement with the knowledge that the bioconcentration factor of 3H is approximately 1. In contrast, higher values were found in TOBT, which can be linked to life-history traits.