A comparison of different detection techniques for 137Cs measurements of cattle in vivo

Agricultural lands with farm animals (e.g. cattle) can be significantly affected by radioactive contamination following nuclear or radiation accidents. In order to optimise the techniques for measuring 137Cs in contaminated cattle, selected radiation detectors have been tested and calibrated using volumetric radiation sources. In addition, a mathematical phantom of a cow was created within Monte Carlo simulations. The main aim of the research was to propose a method for making rapid measurements of 137Cs in cattle in vivo/in situ and to select the most suitable measurement set-up. Measurements of contaminated cattle in vivo were carried out in Belarus with one selected detector, and were then compared with measurements of meat in a laboratory and with measurements of a control group of cows. The proposed measurement method was also tested on measurements of 137Cs in wild boars in Czechia with higher levels of the 137Cs activity.

Aggregated transfer factors of fresh Cs and Sr pollution to various vegetables from six common European soils - mesocosm experiment

Aggregated transfer factors (Tag) were identified for three common vegetables grown in six common European soils freshly contaminated by 134Cs and 85Sr. The experiment was carried out as a mesocosm experiment in pots with an average soil weight of 15.8 kg per pot. The vegetables were grown one after the other during one vegetation season, in the order lettuce, onion, and radish (the order usually applied in private gardens and small farms). Despite the fact that lettuce was grown in the most contaminated soil, it had the lowest Tag (in m2/kg) of both radionuclides (3.6E-4 for Cs, 2.0E-2 for Sr), while onion had 6.4E-3 for Cs and 3.2E-2 for Sr and radish had 1.9E-3 for Cs and 8.1E-2 for Sr. Potassium supply did not show any statistically significant effect on Cs Tag; there was a significant impact of K on the decrease in Sr Tag. The experiments indicated that Tag is more affected by plant species than by soil type; therefore, selection of plants with a lower capacity to uptake radionuclides may be an important measure to reduce food contamination and thus minimize the committed effective dose.

DETERMINING THE TRANSFER FACTORS FOR ESTIMATES OF THE RADIATION CONTAMINATION OF AGRICULTURAL CROPS

The study aims to provide a basis for measures reducing the consequences of a nuclear accident in its late phase, when plant contamination occurs mainly through the root system. Samples of the above-ground biomass of crops and soil were taken in 2020 in the vicinity of the Temelín and Dukovany nuclear power plants (Czech Republic). The 137Cs activities were determined using gamma spectrometry, and the 90Sr activities were measured through beta radiation. From the obtained values, the radionuclide transfer factors (TFs) from soil to crop biomass were calculated. The average area activity of 137Cs in the soil around Dukovany and Temelín was 1700 and 2400 Bq m-2, respectively. The average area activity of 90Sr around Dukovany and Temelín was 211 and 184 Bq m-2, respectively. The TF 137Cs ranged from < 6.3 × 10-6 to 7.9 × 10-3, with a mean of 3.5 × 10-4 m2 kg-1, and the TF 90Sr ranged from 2.7 × 10-4 to 6 × 10-2, with a mean of 1.7 × 10-2 m2 kg-1.

RADON INHALATION EXPERIMENTS TO TEST RADON EXHALATION KINETICS

Three experiments were conducted with a volunteer to test the kinetics of the 222Rn exhalation after a short-time exposure to an elevated 222Rn air concentration. Radon concentration in an exhaled air was measured, complemented by whole body counting of 222Rn decay products in a body. Exhaled activities are compared with the prediction of the recent ICRP biokinetic model for radon. While a rapid equilibration of the exhaled radon activity concentration with that in the air inhaled corresponded with the model, the measured 222Rn exhalation rate was significantly less than modelled. Five hours after termination of the inhalation phase, the radon concentration in the exhaled air decreased to levels expected for non-elevated indoor radon activity concentration. Whole body activities of the 222Rn decay products were found higher than expected. Inhalation of the unattached fraction or residual activity of decay products in the air inhaled may be the explanation.

EMERGENCY PREPAREDNESS OF GAMMA SPECTROMETRY LABORATORIES

Currently, the territorial Radiation Monitoring Network (RMN) of the Czech Republic consists of seven laboratories equipped with gamma spectrometry High Purity Germanium (HPGe) detectors. From 2007 to 2018, five emergency exercises were carried out to test the sample throughput of these facilities and their staff. The main objective was to identify weaknesses and problem areas in the whole process from the moment of obtaining the samples to logging the results into the central RMN database. The long-term aim of these exercises is to optimize emergency response procedures. The most important factor limiting laboratory capacity is the lack of qualified personnel. The exercises showed that in the current state, these laboratories would be able to operate in 12-hour shifts for 14 days and analyze 1700 samples per day. Emergency exercises have highlighted the fact that this type of exercise should be repeated periodically in order to monitor the performance and analytical capabilities of RMN.

OPTIMIZATION OF THE RADIOACTIVE AEROSOL SAMPLING AND MEASURING PROCEDURE WITH RESPECT TO RADON CONCENTRATION IN THE AIR

High-volume aerosol samplers combined with laboratory analysis using high-resolution gamma ray spectrometry allow determining artificial radionuclides in the atmosphere at sub μBq/m3 levels. A major drawback of this procedure is a significant delay of the analysis result after any potential radioactive contamination deposition on the aerosol filter. Within the scope of the HAMRAD project, an autonomous device was developed in order to increase the sampling and measuring frequency. This approach yields higher detection limits (minimum detectable activity concentration [MDAC]) due to the deposited activity of radon decay products on the filter. In order to quantify the radon effect, a simple mathematical model was developed to predict MDAC for the particular radionuclide of interest for the given background conditions. It was found that MDAC can vary by a factor of ~2 for typical 'radon' conditions (~10 Bq/m3) at SÚRO Prague and by a factor up to 5 for high radon concentration (100 Bq/m3).

Potential Source Apportionment and Meteorological Conditions Involved in Airborne 131I Detections in January/February 2017 in Europe

Traces of particulate radioactive iodine (¹³¹I) were detected in the European atmosphere in January/February 2017. Concentrations of this nuclear fission product were very low, ranging 0.1 to 10 μBq m^-3 except at one location in western Russia where they reached up to several mBq m^-3. Detections have been reported continuously over an 8-week period by about 30 monitoring stations. We examine possible emission source apportionments and rank them considering their expected contribution in terms of orders of magnitude from typical routine releases: radiopharmaceutical production units > sewage sludge incinerators > nuclear power plants > spontaneous fission of uranium in soil. Inverse modeling simulations indicate that the widespread detections of ¹³¹I resulted from the combination of multiple source releases. Among them, those from radiopharmaceutical production units remain the most likely. One of them is located in Western Russia and its estimated source term complies with authorized limits. Other existing sources related to ¹³¹I use (medical purposes or sewage sludge incineration) can explain detections on a rather local scale. As an enhancing factor, the prevailing wintertime meteorological situations marked by strong temperature inversions led to poor dispersion conditions that resulted in higher concentrations exceeding usual detection limits in use within the informal Ring of Five (Ro5) monitoring network.

Behaviour of 137Cs in forest humus detected across the territory of the Czech Republic

The activity concentration of ¹³⁷Cs in samples of coniferous forest humus collected across the territory of the Czech Republic in 1995 and 2005 was analysed, and it was found significantly correlated with the surface deposition caused by the Chernobyl accident. The effective (12.8 y) and environmental (22.3 y) half-lives of radiocaesium in humus were calculated and compared with those in spruce bark. The impact of important forest stand factors, that is, precipitation, content of organic matter, age of trees and pH, on the behaviour of ¹³⁷Cs in humus was studied. It was observed that humus samples with a higher proportion of organic matter, higher pH(H2O) and pH(CaCl2) contained higher amounts of ¹³⁷Cs. Conversely, with the age of trees, the activity concentration of ¹³⁷Cs in humus is decreasing. Higher precipitation and humus acidity decrease the reduction rate of the ¹³⁷Cs in humus. These stand factors increase bioavailability of ¹³⁷Cs in humus. The transfer and retention of available ¹³⁷Cs in biomass of organisms living in humus for a long time can satisfactorily explain the longer residence time of ¹³⁷Cs in humus affected by the studied factors.

Long-term retention of (137)Cs in three forest soil types with different soil properties

Current (137)Cs activity concentrations were studied at three localities in individual soil horizons of Stagnosol, Arenic Podzol and Haplic Cambisol soil units in soil blocks with dimensions of 20 × 20 × 40 cm situated below pine canopies (n = 3) and spruce canopies (n = 3), and below small canopy gaps, at least 15 × 15 m in area (n = 3 + 3), which have probably endured since 1986. The main zone of (137)Cs accumulation in all the localities was found to be in the organic horizons (H and F). No significant transport and accumulation of (137)Cs into illuvial soil horizons (Bm, Bs or Bhs, Bv and Bv/IIC) was found. The estimated current total (137)Cs activity concentrations in the soil blocks 40 cm in depth were only slightly higher below the coniferous canopy than they were below nearby canopy gaps. The inventory of (137)Cs in the soils was found to be in accordance with the estimated (137)Cs inputs from the Chernobyl fallout and from global fallout. The low amounts of (137)Cs found accumulated in the aboveground biomass (mosses, grasses, needles) did not substantially bias the studied radiocaesium balance in the soils. The vertical migration rate of (137)Cs in soils (cm/year) had a tendency to be higher below canopies than below canopy gaps and below pine canopies than below spruce canopies. We expected the current (137)Cs activity concentrations in the individual soil horizons to be related to the studied soil parameters: pH (H2O), pH (CaCl2), content of organic matter and mineral portion and portion of humic and fulvic acid contents (Q4/6). However, this was not confirmed. Similarly, we observed a weak tendency toward higher (137)Cs activity in soils below the canopy than in soils below canopy gaps. The available gaps used in our study may have been too small, and they may have been affected by an accumulation of litter and humus containing (137)Cs from the surrounding plots situated below neighbouring canopies.

Variation of ²¹⁰Po daily urinary excretion for male subjects at environmental level

(210)Po was determined in 24-h urine of seven healthy males from Prague, Czech Republic, for ten consecutive days. The results show that for each volunteer, the urinary excretion of (210)Po changed only little from day to day in the studied time period. For two volunteers, the difference in the daily excreted (210)Po activity for two consecutive days was not significant, given the 95% confidence interval (two sigma) of the activity measurements. The same is valid for the excretion data of the other volunteers, except for some days where the differences were slightly higher. The range of daily urinary excretion of (210)Po of each volunteer in the studied time period was quite narrow. Among the volunteers, the maximum daily urinary excretion value of (210)Po was at most about a factor of 2.5 higher than the lowest excretion value. An attempt to explain the observed small inter-individual variability of (210)Po excretion in daily urine is made.

Monitoring radionuclides in the atmosphere over the Czech Republic after the Fukushima Nuclear Power Plant accident

This paper presents the results of atmospheric radioactivity monitoring over the Czech Republic, as obtained by the Radiation Monitoring Network, following the Fukushima Dai-Ichi Nuclear Power Plant accident. Maximum values for (131)I were 5.6 mBq m(-3) in aerosol form and 13 mBq m(-3) in gaseous form. The maximum values for (134)Cs and (137)Cs were 0.64 and 0.72 mBq m(-3), respectively. The estimated effective half-time for removing the activity from the atmosphere was 6-7 d and 3.5 d for caesium and iodine, respectively. The gaseous-to-total activity ratios of (131)I ranged between 0.3 and 0.9, with an arithmetic mean value of 0.77. The mean value for the (134)Cs/(137)Cs ratios was close to 1.0. The effective inhalation dose due to the accident for an adult living in the Czech Republic was estimated at <4 × 10(-5) mSv, out of which the proportion of (131)I was 88%.

Radiocaesium levels in game in the Czech Republic

The paper summarizes results of monitoring of (137)Cs activities in game species roaming in the woods over the territory of the Czech Republic for the time interval of 1986-2012. Geometric means and other statistical characteristics were estimated from the data sets on the assumption of log-normal distribution of the data from the time interval 2004-2012 where the character of data distribution had displayed no significant change. Geometric means (in Bq/kg) in meat were: wild boar 5.1, red deer 1.9, roe deer 0.77 and feathered game 0.14. The mean value in the less frequent game amounted to 0.36 Bq/kg. The geometrical standard deviation (GSD) widely varied from 1.6 to 21 for the studied species. Based on mass activity dependence on time, we assessed the effective and environmental half-lives of activity decline. For red deer and roe deer, the effective (137)Cs half-life was 2.9 and 3.2 years, and environmental half-life 3.2 and 3.6 years respectively. The effective half-life of (137)Cs in wild boar of 38 years was determined with large uncertainty and it shows constant influx of (137)Cs activity to the digestive tract of wild boars. A statistically significant season-based (137)Cs level was found in red deer and wild boar. Higher winter and spring activities of (137)Cs in wild boar are linked with decreasing access to naturally occurring food with lower (137)Cs content (chestnuts, acorns, and beech nuts), making boar grub around for ground-deposited food (often for mushrooms with higher activity). Higher winter activities of (137)Cs in red deer meat, most probably, are due to lower access to green diet in winter. The average annual committed effective dose for Czech population based on estimates of game species meat consumption between 2004 and 2012 was insignificant, only 0.03 μSv.

Long-term behaviour of 137Cs in spruce bark in coniferous forests in the Czech Republic

Activity concentrations of (137)Cs were detected in more than 400 outer spruce bark samples collected at sites variably affected by Chernobyl fallout across the Czech Republic in 1995 and 2010. The temporal changes in the (137)Cs activities were found. The mean effective half-life (TEF) for (137)Cs in spruce bark was 9.6 years, and the mean environmental half-life (TE) was 14 years. The effective half-lives were significantly higher in areas with higher long-term annual precipitation sums. Coefficient a in linear regression y = ax + b of half-lives on precipitation sums was 0.015 y mm(-1) for TEF and 0.036 y mm(-1) for TE. The aggregated transfer factor of (137)Cs from soil to bark was determined and the pre-Chernobyl bark contamination related to year 2010 was estimated.

Long-term ¹³⁷Cs activity monitoring of mushrooms in forest ecosystems of the Czech Republic

This paper reports on results of activity mass concentration analyses performed in various forest mushrooms in the Czech Republic within 1986 and 2011. The estimated effective half-life of (137)Cs and its environmental half-life (i.e. the effective half-life minus the effect of physical decay) were found to be 5.6 ± 0.6 and 6.9 ± 0.7 y, respectively. Non-homogeneity in (137)Cs surface contamination over the country's territory and fungus species-based (137)Cs accumulation capacity then account for a span of up to 4 orders of magnitude in activity mass concentrations measured each year after the Chernobyl accident. The highest geometric activity mass concentration (Bq kg(-1) of dry weight) means of (137)Cs (obtained from samples between years 2004 and 2011) were measured in Suillaceae (1050 Bq kg(-1)) and Boletus badius (930 Bq kg(-1)), the lowest in Agaricus (1 Bq kg(-1)). The geometric mean of all mushrooms amounted to 230 Bq kg(-1), being 440 Bq kg(-1) in Boletales, 150 Bq kg(-1) in Russulales and 21 Bq kg(-1) in Agaricales. Geometric standard deviation levels were generally high. The highest Cs accumulation capacity was observed in Boletales (namely in Suillaceae), while the lowest in Agaricales, being over 3 orders of magnitude lower than in Suillaceae.

Particle size distribution of radioactive aerosols after the Fukushima and the Chernobyl accidents

Following the Fukushima accident, a series of aerosol samples were taken between 24th March and 13th April 2011 by cascade impactors in the Czech Republic to obtain the size distribution of (131)I, (134)Cs, (137)Cs, and (7)Be aerosols. All distributions could be considered monomodal. The arithmetic means of the activity median aerodynamic diameters (AMADs) for artificial radionuclides and for (7)Be were 0.43 and 0.41 μm with GDSs 3.6 and 3.0, respectively. The time course of the AMADs of (134)Cs, (137)Cs and (7)Be in the sampled period showed a slight decrease at a significance level of 0.05, whereas the AMAD pertaining to (131)I increased at a significance level of 0.1. Results obtained after the Fukushima accident were compared with results obtained after the Chernobyl accident. The radionuclides released during the Chernobyl accident for which we determined the AMAD fell into two categories: refractory radionuclides ((140)Ba, (140)La (141)Ce, (144)Ce, (95)Zr and (95)Nb) and volatile radionuclides ((134)Cs, (137)Cs, (103)Ru, (106)Ru, (131)I, and (132)Te). The AMAD of the refractory radionuclides was approximately 3 times higher than the AMAD of the volatile radionuclides; nevertheless, the size distributions for volatile radionuclides having a mean AMAD value of 0.51 μm were very close to the distributions after the Fukushima accident.

Tracking of airborne radionuclides from the damaged Fukushima Dai-ichi nuclear reactors by European networks

Radioactive emissions into the atmosphere from the damaged reactors of the Fukushima Dai-ichi nuclear power plant (NPP) started on March 12th, 2011. Among the various radionuclides released, iodine-131 ((131)I) and cesium isotopes ((137)Cs and (134)Cs) were transported across the Pacific toward the North American continent and reached Europe despite dispersion and washout along the route of the contaminated air masses. In Europe, the first signs of the releases were detected 7 days later while the first peak of activity level was observed between March 28th and March 30th. Time variations over a 20-day period and spatial variations across more than 150 sampling locations in Europe made it possible to characterize the contaminated air masses. After the Chernobyl accident, only a few measurements of the gaseous (131)I fraction were conducted compared to the number of measurements for the particulate fraction. Several studies had already pointed out the importance of the gaseous (131)I and the large underestimation of the total (131)I airborne activity level, and subsequent calculations of inhalation dose, if neglected. The measurements made across Europe following the releases from the Fukushima NPP reactors have provided a significant amount of new data on the ratio of the gaseous (131)I fraction to total (131)I, both on a spatial scale and its temporal variation. It can be pointed out that during the Fukushima event, the (134)Cs to (137)Cs ratio proved to be different from that observed after the Chernobyl accident. The data set provided in this paper is the most comprehensive survey of the main relevant airborne radionuclides from the Fukushima reactors, measured across Europe. A rough estimate of the total (131)I inventory that has passed over Europe during this period was <1% of the released amount. According to the measurements, airborne activity levels remain of no concern for public health in Europe.

Retrospective determination of 137Cs specific activity distribution in spruce bark and bark aggregated transfer factor in forests on the scale of the Czech Republic ten years after the Chernobyl accident

The (137)Cs specific activities (mean 32Bq kg(-1)) were determined in spruce bark samples that had been collected at 192 sampling plots throughout the Czech Republic in 1995, and were related to the sampling year. The (137)Cs specific activities in spruce bark correlated significantly with the (137)Cs depositions in areas affected by different precipitation sums operating at the time of the Chernobyl fallout in 1986. The ratio of the (137)Cs specific activities in bark and of the (137)Cs deposition levels yielded bark aggregated transfer factor T(ag) about 10.5×10(-3)m(-2)kg(-1). Taking into account the residual specific activities of (137)Cs in bark 20Bq kg(-1) and the available pre-Chernobyl data on the (137)Cs deposition loads on the soil surface in the Czech Republic, the real aggregated transfer factor after and before the Chernobyl fallout proved to be T*(ag)=3.3×10(-3)m(-2)kg(-1) and T**(ag)=4.0×10(-3)m(-2)kg(-1), respectively. The aggregated transfer factors T*(ag) for (137)Cs and spruce bark did not differ significantly in areas unequally affected by the (137)Cs fallout in the Czech Republic in 1986, and the figures for these aggregated transfer factors were very similar to the mean bark T(ag) values published from the extensively affected areas near Chernobyl. The magnitude of the (137)Cs aggregated transfer factors for spruce bark for the pre-Chernobyl and post-Chernobyl period in the Czech Republic was also very similar. The variability in spruce bark acidity caused by the operation of local anthropogenic air pollution sources did not significantly influence the accumulation and retention of (137)Cs in spruce bark. Increasing elevation of the bark sampling plots had a significant effect on raising the remaining (137)Cs specific activities in bark in areas affected by precipitation at the time when the plumes crossed, because the sums of this precipitation increased with elevation (covariable).

Low background shielding of HPGe detector

National Radiation Protection Institute in Prague is equipped with 14 HPGe detectors with relative efficiency up to 150%. Steel shielding with one of these detectors (relative efficiency 100%) was chosen to be rebuilt to decrease minimum detectable activity (MDA). Additional lead and copper shielding was built up inside the original steel shielding to reduce the volume of the inner space and filled with nitrogen by means of evaporating liquid nitrogen. MDA values decreased for Compton background up to 0.67 of original value.