7Be Activity Concentrations Research Articles

Long-term investigations of radioactive matter in the air of Zagreb, Croatia

Investigations on the distribution and fate of naturally occurring, nuclear-weapons-produced, and reactor-released radionuclides in the city of Zagreb, Coatia, have been conducted as part of the monitoring program for radioactive contamination of the human environment in Croatia since the early 1960s. This paper describes long-term investigations of man-made 137Cs and naturally occurring 7Be in the city of Zagreb after the Chernobyl accident. The Chernobyl nuclear accident caused a major increase in 137Cs activity concentrations only in 1986, which quickly decreased over the next few years to pre-Chernobyl values. The observed mean residence time for 137Cs in the air during the post-Chernobyl period from January 1987 to December 1990 was estimated to be 1.0 year. During this period, the observed mean residence time for 137Cs in fallout was estimated to be 0.9 years. The mean 7Be activity concentration in the air from 1987 to 2004 was (5.4 ± 2.8) × 10 − 3 Bq m − 3 . The measured 7Be activity concentrations showed seasonal behavior with the highest usually measured in July. Despite the constant presence of radioactive matter in the Zagreb air during the observational period, activity concentration values never exceeded legal limits. Consequently, 137Cs doses incurred by inhaling contaminated air after the Chernobyl accident were very small.

An efficiency calibration for 210Pb and 7Be measurements by gamma-ray spectrometry in atmospheric filters

Natural radionuclides, especially 210Pb and 7Be, condensed on suspended particulate matter in the atmosphere (commonly called aerosols) have been widely used to study a large variety of relevant atmospheric processes. A rapid and non-destructive analysis of 210Pb and 7Be is possible by direct measurement of their 46.5 and 477.6 keV γ-rays, respectively. In this work we have developed an original method to find an empirical function which relates the full-energy peak efficiency with energy in a rectangular geometry for energies above 150 keV. For the energy range below 150 keV only the 46.5 keV of the gamma photon of 210Pb was of interest in this work. A dusty Reference Material (phosphate rock) containing high levels of 238U-series radionuclides, especially 226Ra, was used as calibration sample. This solid matrix (grain size smaller than 63 μm) was taken to impregnate homogenously the filters so that the real geometry of measurement was reproduced. 210Pb and 7Be activity concentrations in surface air were determined in samples collected from July 2004 to June 2005 at three different locations of the Huelva province (South West of Spain): urban, rural, and industrialized areas. 7Be and 210Pb activities have been determined in the PM 10 and TSP fractions of surface aerosols. The radiometric measurements were performed by low-level gamma spectrometry with a thin window coaxial germanium detector.

Distribution of radiocesium and natural gamma emitters in pine needles in coniferious forest sites of Izmir

Using a high-resolution gamma-spectrometer system, the activity concentrations of 7Be, 137Cs, 40K and 226Ra were determined in the pine needles. Activity concentrations of the concerned radionuclides in the needle samples were as follows: 7Be, 24.6±2.40 to 210±7.21 Bq kg −1, 40K, 23.5±12.4 to 287±15.6 Bq kg −1, 226Ra, 0.44±0.12 to 12.3±2.18 Bq kg −1, and 137Cs, 0.61±0.30 to 2.29±0.38 Bq kg −1. It is found that the frequency distributions obtained for 7Be and 137Cs can be fitted to a normal distribution, and for 40K and 226Ra can be fitted to a log-normal distribution.

LONG-TERM MONITORING OF RADIOACTIVITY IN SURFACE AIR AND DEPOSITION IN NEW YORK STATE

Gross-beta activities have been determined weekly for 22 y from filtered atmospheric aerosols at seven sites in New York State. The activities, ranging from 0.1 to 0.9 mBq m(-3), varied seasonally and were evaluated in terms of meteorological factors. Cosmogenic beryllium (7Be) concentrations were determined quarterly on the air filters and weekly in deposition collected at one site. Over 98% of the air filters contained observable activity concentrations of 7Be (mean of 3 mBq m(-3)) and 210Pb (mean of 1 mBq m(-3)). However, only 20% of deposition samples contained Be concentrations above analytical detection limits. Tritium (3H) concentrations were below detection limits in deposition samples at the background site, but were present on most samples collected near a H-processing facility. Measurements of 131I were conducted weekly on charcoal canisters, with only one site showing observable concentrations (mean of 1 mBq m(-3)), due to nearby incineration of dried municipal sludge containing patient waste from hospital treatments.

Deposition velocities and washout ratios on a coastal site (southeastern Spain) calculated from 7Be and 210Pb measurements

The activity concentrations of 7Be and 210Pb were measured in Málaga, Southeastern Spain (36°43′40″N; 4°28′8″W) in aerosols, precipitation and dry fallout continuously and systematically for 8 years. At the same sampling point, aerosols were collected weekly on filters and monthly precipitation sampling was carried out to study deposition. The air concentration of 7Be showed a seasonal increase during the spring and summer months while the air concentration of 210Pb was greater in summer. The concentration data of 7Be and 210Pb together with meteorological variables were used for a comprehensive analysis of variations. The specific activities of 7Be and 210Pb in bulk deposition samples showed a similar seasonal trend variation to that of the aerosols concentrations. Using the concentrations of 7Be and 210Pb in air and their depositional fluxes, the deposition velocities of aerosols and washout ratios were calculated. The mean deposition velocity of 7Be and 210Pb over the 8-year period is 0.4 and 1.5 cm s −1, respectively, and the corresponding washout ratios are 477 and 1908, respectively. The results showed a prevailing influence of amount of rainfall for deposition velocities and other factors such as TSP, the number of rainy days and the number of dry days for washout ratios. A comparison of our measurements and other data obtained at different locations in the world was also made.

Precipitation scavenging of 7Be and 137Cs radionuclides in air

Atmospheric depositional fluxes of the naturally occurring 7Be of cosmogenic origin and 137Cs from fallout of the Chernobyl accident were measured over a 6-year period (January 1987–December 1992) at Thessaloniki, Greece (40°38′N, 22°58′E). Total precipitation accumulation during 1987–1992 varied between 33.7 cm and 65.2 cm, reflecting a relatively dry (precipitation-free) climate. The activity concentrations of 7Be and 137Cs in rainwater depended on the precipitation rate, being higher for low precipitation rates and lesser for high precipitation rates. 137Cs was removed by rain and snow more efficiently than 7Be. Snowfall was more efficient than rainfall in removing the radionuclides from the atmosphere. The annual bulk depositional fluxes of 7Be varied between 477 and 1133 Bq m −2 y −1 and this variability was attributed to the amount of precipitation and the variations of the atmospheric concentrations of 7Be. The annual bulk depositional fluxes of 137Cs showed a significant decrease over time from 1987 to 1992, resulting in a removal half-life of 1.33 years. The presence of 137Cs in air, and therefore in rainwater and snow, long after the Chernobyl accident (26 April 1986) was mainly due to the resuspension process. The normalized depositional fluxes of both radionuclides showed maximal values during the spring season where the maximum amount of precipitation occurred. The relatively high positive correlation between 7Be and 137Cs normalized depositional fluxes indicates that the scavenging process of local precipitation controlled the fluxes of both radionuclides. The dry depositional flux of 7Be was less than 9.37% of total (wet and dry) depositional flux. The fraction of dry-to-total depositional flux of 137Cs was much higher than that of 7Be, due to the resuspended soil.

Temporal changes of 7Be and 210Pb concentrations in surface air at temperate latitudes (40°N)

Atmospheric concentrations of 7Be and 210Pb were measured for 15 years (1987–2001) in ground-level air at Thessaloniki, Northern Greece (40°38′N, 22°58′E). Mean activity concentrations of 7Be and 210Pb were 5.02 mBq m −3 and 664 μBq m −3, respectively, characteristic of the latitude of 40°N. Monthly atmospheric concentrations of 7Be showed a strong seasonal trend with the highest values being observed in the summer and the lowest in the winter period. Multiple regression analysis of the data of 7Be concentrations and a number of meteorological parameters revealed that the sunspot number and temperature are the most significant parameters affecting the concentrations of 7Be in surface air. The observed strong positive correlation between the mean monthly concentrations of 7Be and the temperature confirms that the increased rate of vertical transport within the troposphere, especially during the warm months, has as a result to carry down to the surface layer air masses enriched in 7Be. Highest values of the mean monthly atmospheric concentrations of 210Pb were observed in the autumn and lowest in the spring period. The positive correlation that was observed between 210Pb and 7Be concentrations during the summer months suggests that these two radionuclides could be used together as tracers of environmental processes.

Seasonal variations in activity concentrations of137Cs,40K,7Be,228Ra,99Tc,90Sr, and $^{239,240}$Pu in Fucus vesiculosus and Ascophyllum nodosum from the southeastern coast of Norway

The aim of this study was to compare the indicator properties of Fucus vesiculosus and Ascophyllum nodosum. Activity concentrations of 137Cs, 40K, 7Be, 228Ra, 99Tc, 90Sr and Pu were measured in plants of the two species collected monthly in 2002 from one location at the southeastern coast of Norway. For 40K, 137Cs, 90Sr, 7Be and 228Ra the activity concentrations were significantly higher in Fucus vesiculosus than in Ascophyllum nodosum, whereas the opposite was the case for 99Tc. For 137Cs, 90Sr, 7Be and 228Ra the temporal variations in activity concentrations showed similar pattern for the two species, whereas for 99Tc the temporal pattern was different for the two species. The observed temporal variations in activity concentrations of 137Cs (both species) and 90Sr (only Fucus vesiculosus) correlate with expected variations in seawater concentrations. For 137Cs salinity, light conditions, temperature and growth rates seem to work in the same direction as the variations in seawater concentrations. A lack of correlation between salinity and 99Tc concentrations in the algae indicates a slower dynamic in uptake and/or secretion for technetium. The observed differences between the two species may partly be explained by the difference in growth rate and life length between the two species.

The temporal variations of 7Be, 210Pb and 210Po in air in England

We have conducted measurements of naturally occurring radionuclides 7Be, 210Pb and 210Po in air at ground level at Chilton, Oxfordshire, England. The sampling and analysis regime for the latter two isotopes has been optimised to minimise uncertainties in measurement due to decay of 210Po and in-growth of 210Pb during the sampling and analysis period. Analysis times were reduced by using Cerenkov counting to assay the 210Bi daughter of 210Pb. Monthly data collected over a four-year period are presented and discussed. 7Be activity concentrations appear to peak in spring. 210Pb activity concentrations also follow a seasonal trend reflecting different 222Rn emanation rates from soil during winter and summer. Data for 210Po show no such trend.

A study of the vertical diffusion of the cosmogenic radionuclides, 7Be and 22Na in the atmosphere

The study of the mean vertical concentration profile of cosmogenic radionuclides provides information on the vertical transport in the troposphere and stratosphere. This paper is based on the results of accurate measurements of the mean monthly activity concentrations of 7Be and 22Na in ground-level air, data of the production rate of cosmogenic radionuclides in the atmosphere and a one-dimensional steady-state diffusion equation numerically solving the finite difference approximation.

Long-term environmental monitoring and application of low-level 3H, 7Be, 137Cs and 210Pb activity concentrations in the non-biotic compartments of the Danube in Austria

The aim, methods, and results of long-term low-level measurements of 3H, 7Be, 137Cs and 210Pb in water and sediment of the Austrian part of the Danube are presented. The results are discussed focused on recent and obvious future applications in applied radioecology and environmental research. The long-term radiometric data supported by the low-level monitoring program act as basis for ecological modelling and environmental assessment.

Concentration measurements of 7Be at ground level air at Palermo, Italy—comparison with solar activity over a period of 21 years

Air activity concentrations of 7Be in Palermo determined for the period January 1995–December 2002 by γ-ray spectrometric analysis of particulate samples collected on paper filter by a high-volume sampler (~900 m 3 h −1) are reported. The temporal behaviour of 7Be concentration presents the same characteristics already observed in the measurements carried out over the previous 13-year (1982–1994) investigated period. The mean value of 5.06 mBq m −3 obtained from the analysis of the 4636 particulate samples collected from 1982 to 2002 can be considered a representative value of 7Be air concentration at ground level in our geographical zone. The comparison of long-term variation in the 7Be concentrations with the cyclic solar activity—extended to the whole period of 21 years—confirms the inverse correlation between the two quantities.

Study of removal processes of 7Be and 137Cs from the atmosphere

In order to understand better the way in which radioactive contamination may be transferred from the atmosphere to other ecological compartments it is necessary to obtain information of the deposition mechanisms of radionuclides. Concentration and speciation of 137Cs and 7Be in the atmospheric aerosol and deposition were studied. The mixed deposition velocities of water-soluble and insoluble 137Cs and 7Be were determined. The relation between activity concentrations of insoluble 7Be in the atmosphere and its amount in deposition was observed. It is supposed that in the deposition process of radiocesium the precipitation plays an important role in scavenging of water-soluble radiocesium by falling raindrops, in contrast to insoluble 137Cs where the dry deposition becomes predominant.

226Ra, 40K and 7Be activity concentrations in plants in the environment of Kaiga, India

Leaves, stem and bark samples from several plant species were collected from tropical forest of Kaiga, in the west coast of India where two nuclear power reactors of 220 MW each have just been commissioned and another two are under construction, and analysed for their 226Ra, 40K and 7Be concentrations. The activities of 226Ra and 40K in plants were found to vary in the range BDL–13.2 and 12.0–797.3 Bq kg −1, respectively. Plants show significant 7Be activity in leaves, the activity varies in 72.5–1060.8 Bq kg -1. Stem and bark of plants show higher levels of 226Ra and 40K when compared to leaves. Soil-to-plant transfer factor for 226Ra and 40K were found to vary in the range BDL–0.37 and 0.09–5.61, respectively for different plants. The concentration of 226Ra and 40K in leaves depends on the age of the leaves.

The potential of lichens as long-term biomonitors of natural and artificial radionuclides

Lichens were used as biomonitors of Chernobyl fallout 137Cs, of cosmogenic 7Be and of radioactive members of the natural uranium and thorium decay chains. Samples were taken from two locations in France, including lichens sampled at different distances of a coal fired power plant and close to a uranium ore processing waste disposal site. All samples were analyzed gamma-spectrometrically after equilibrium concentrations of short-lived isotopes had been attained. Activity concentrations of the members of the uranium and thorium decay chains in Parmelia sulcata sampled 1994 decrease with distance from the plant, whereas in lichens taken at the waste disposal site a decrease with time was observed. Comparison of 7Be activity concentrations measured in lichens with atmospheric deposition rates confirms that P. sulcata can be used as a quantitative biomonitor of radioactive trace substances. Retention half-lives calculated with a simple one-compartment model are 2.6±1.2 years for cesium, which was detected in all samples even more than a decade after the Chernobyl accident, and of 0.7 (±0.1) to 3.3 (±0.7) years for lead. Consequences of our results for model identifiability and parameter estimation of a two-compartment model are discussed.

A climatology of 7Be at four high-altitude stations at the Alps and the Northern Apennines

The 7Be activity concentrations measured from 1996 to 1998 at four high-altitude stations, Jungfraujoch—Switzerland, Zugspitze—Germany, Sonnblick—Austria and Mt. Cimone—Italy, were analyzed in combination with a set of, meteorological and atmospheric parameters such as the tropopause height, relative and specific humidity and also in conjunction with 3D back-trajectories in order to investigate the climatological features of 7Be. A frequency distribution analysis on 7Be activity concentrations revealed the existence of two concentration classes around 1.5 and 6 mBq m −3 and a transition class between the two modes of the distribution at 3–4 mBq m −3. Cross-correlation analysis performed between 7Be and a number of meteorological and atmospheric parameters at the first three stations showed a strong negative correlation with relative humidity (−0.56, −0.51, −0.41) indicating the importance of wet scavenging as a controlling mechanism. Also, the positive correlation with the height of 3-days back-trajectories and tropopause height (+0.49/+0.43, +0.59/+0.36, +0.44/+0.38) shows that downward transport from the upper or middle to lower troposphere within anticyclonic conditions plays also an important role. Trajectory statistics showed that low 7Be concentrations typically originate from lower-altitude subtropical ocean areas, while high concentrations arrive from the north and high altitudes, as is characteristic for stratospheric intrusions. Although the 7Be activity concentrations are highly episodic, the monthly means indicate an annual cycle with a late-summer maximum at all stations. The correlation coefficients calculated for monthly means of the 7Be and atmospheric data suggest that the main predictor controlling the seasonality of the 7Be concentrations is tropopause height (+0.76, +0.56, +0.60), reflecting more vertical transport from upper tropospheric levels into the lower troposphere during the warm season than during the cold season.

Trajectory Analysis of 210Pb and 7Be in Ground-Level Air in Southern Finland

The Finnish Meteorological Institute has been monitoring airborne natural radionuclides 210Pb and 7Be at its geophysical observatory at Nurmijuarvi, southern Finland (60°30'N, 24°39'E, h = 105 m above see level). Daily aerosol samples (3500 m3/d) were collected onto glass-fiber filters with an aerosol sampler having an aerodynamic cutoff diameter of 10-15 μm depending on the wind speed. The filters were analysed for 7Be with an electrically cooled HPGe γ-ray spectrometer and for 210Pb with α-counting of the daughter 210Po using an automatic α/β-analyzer. A trajectory analysis of the observed activity concentrations revealed that the highest 7Be and 210Pb activity concentrations are associated with continental air masses coming from southeast. Meteorologically these situations often originate from high-pressure areas in central Russia. The associated air masses are often dry, which prevents the removal of radionuclides through precipitation scavenging. 222Rn, and thus 210Pb too, originate practically entirely from land areas and not from oceans. The descending movement of air in high-pressure areas promotes the transfer of 7Be from upper air to the ground level. The production of 7Be increases toward the magnetic poles of the Earth. This is not reflected in the source areas of 7Be, because the concentration variations in the ground-level air are due to large-scale weather phenomena.

Source areas of airborne 7Be and 210Pb measured in Northern Finland.

Daily aerosol samples were collected at Sodankylä, Northern Finland, from July 1995 to June 1997. The filter samples were analyzed for 7Be by semiconductor gamma spectrometry and for 210Pb by alpha counting of the in-grown 210Po. The concentrations were lognormally distributed with median concentrations of 2,500 and 160 muBq m(-3) for 7Be and 210Pb, respectively. The trajectory analysis performed showed that the highest 210Pb activity concentrations were associated with continental air masses originating in Central Russia. High 7Be activity concentrations were found in air masses from Central Russia and, during springtime, also in air masses coming from southwest. The latter cases were attributed to the transfer of stratospheric air masses into the troposphere along the polar front. Slightly elevated 7Be and 210Pb concentrations were found in air masses coming to Sodankyla from northwest between 70th and 80th latitudes. This was attributed to the long-range transport from continental North America.

Factors controlling beryllium-7 at Jungfraujoch in Switzerland

7Be activity concentrations were measured at the alpine research station at Jungfraujoch (JFJ), Switzerland, (07°59'E/46°32'N/3580 m asl) from 4 April 1996 to 1 January 1997 with a time resolution of 2 days using gamma spectroscopy. The data were analysed in relation to meteorological parameters (potential temperature at tropopause level, relative humidity, potential temperature at JFJ), and total ozone at Arosa in eastern Switzerland. Composite 500 hPa geopotential height maps were computed for days with high and low 7 Be activity concentrations. It was found that downward transport associated with an upper ridge and a high tropopause is a significant controlling mechanism for high 7 Be activity concentrations at JFJ. In addition, wet scavenging is also important. A multiple linear regression model using potential temperature at tropopause level and relative humidity at JFJ as predictors explained 60% of the variability in the 7 Be activity concentrations over the investigated period. The results indicate that the indirect influence of stratosphere-troposphere exchange (STE) to the 7 Be activity concentrations at JFJ may be more important than the direct one during the period under investigation. The vigorous downward transport of stratospheric air to JFJ may be considered as the direct influence from STE, whereas a multi-step transport process with a longer tropospheric age of the stratospheric air masses may be considered as the indirect one. The indirect influence of stratosphere-troposphere exchange is investigated in a case study in which the highest 7 Be concentration, occurring from 16 to 23 July at JFJ, is associated with stratosphere-troposphere transport above northern Europe and strong southward advection with subsequent subsidence.

The role of suspended particles in the discharge of 210Pb and 7Be within the Kuji River watershed, Japan

Fluvial discharge of atmospherically-derived 210Pb and 7Be was studied in the Kuji River watershed in Japan. The daily load of 210Pb and 7Be, associated with suspended particles, greatly increased during high-flow conditions. However, the activity concentrations of 210Pb and 7Be in the suspended particles were found to be rather independent of the flow rate. Due to this feature, the daily load of the activities associated with the suspended particles was mainly controlled by that of the suspended particles. Compared with the other reported values, the estimated mean residence time of atmospherically-derived 210Pb in the present study was rather short (about 800 years), possibly reflecting the high availability of the suspended particles eroded from the top soil in the watershed. The annual load of 210Pb and 7Be was predominantly of particulate form (approx 90%). These results suggest that the fluvial discharge of atmospherically-derived, highly adsorptive (k d ≳ 10 4 mg l −1) radionuclides in a river watershed is primarily due to the discharge of suspended particles, which strongly depends on the flow rate of river water and also on the location of the watershed.