Mechanism of 7Be scavenging from the atmosphere through precipitation in relation to seasonal variations in Rokkasho Village, Aomori Prefecture, Japan

⁷Be deposition fluxes and atmospheric concentrations were measured at Rokkasho Village, Aomori Prefecture, Japan, from 2000 to 2005. It was confirmed that the ⁷Be deposition fluxes were minimum in summer, and the fallout maximizes in winter. The atmospheric concentration of ⁷Be was especially low in summer, and high in the other three seasons. A positive correlation was observed between the amount of precipitation and ⁷Be deposition. Clear seasonal differences were evident among the ratios of ⁷Be deposition flux to precipitation amounts in the four seasons. The ratios were especially high in winter, higher than those in the other three seasons. ⁷Be deposition flux was estimated by a simple simulation model using atmospheric ⁷Be concentrations and local meteorological data. As a result, the estimated deposition value was relatively lower than the measured value in winter.     

Analysis of the temporal evolution of atmospheric7Be as a vector of the behavior of other radionuclides in the atmosphere

The mean weekly levels of⁷Be in the atmosphere of Cáceres (Spain) was measured for three consecutive years, from 1992 to 1994. The values showed a strongly seasonal behavior, conditioned fundamentally by two effects: (1) the incorporation of⁷Be into the low layers of the troposphere due to the displacement of masses of air from higher layers caused by the solar irradiation, and (2) the washing of⁷Be out of the atmosphere by rain. From the quantification of these two effects, the residence time of⁷Be was determined in the atmosphere at ground level as 10.3 days, with an interval for the standard error of 9.0 and 12.1 days. Modelling the temporal evolution of this radionuclide we were able to explain 90.72% of the variance of the measured activity levels. Using the effective residence time of⁷Be, we were able to justify the diversity of values obtained for the deposition of¹³⁷Cs in different soils of the province of Cáceres due to the fallout from atmospheric nuclear blasts.     

Fallout of7Be in Damascus City

Atmospheric fallout of⁷Be was measured over a 2 year period (January 1995–January 1997) at Damascus city (33 N^o, 727 m above sea level). The annual total deposition of⁷Be was found to be 420 and 634 Bq·m⁻² for 1995 and 1996, respectively, reflecting a Mediterranean climate where two well recognized periods are dominant (wet and dry). The depositions in the wet periods were 303 Bq·m⁻² and 517 Bq·m⁻² for 1995 and 1996, respectively, while unexpected equal deposition rates in the two dry periods were found to be about 117 Bq·m⁻². In addition, monthly deposition rate of⁷Be showed a maxima in February in 1995 and January for 1996. Moreover, a comparison has been set for our measurements and other data obtained at different locations in the world.     

<Superscript>7</Superscript>Be in the lower atmosphere at a mid-latitude (40°N) during the year 2009 of a particular minimum of solar activity

⁷Be activity concentrations were measured in the lower atmosphere at Thessaloniki, Northern Greece (40°38′N, 22°58′E) over the year 2009, a year of a particular minimum of solar activity. The mean annual activity concentration of ⁷Be at that year was 6.01 mBq m⁻³. The variability of ⁷Be surface concentrations related to the solar cycle appeared to be deviated about 40% between the maximum and the minimum values. A positive correlation (R = 0.97) was revealed between the activity concentrations of ⁷Be and the temperature, confirming that the increased rates of vertical transport within the troposphere, especially during the warmer months, resulted in carrying down to the surface layer air masses enriched in ⁷Be. Relatively high values of ⁷Be activity concentrations were observed by increasing of the tropopause height. A negative correlation (R = −0.65) between the ⁷Be activity concentrations and the relative humidity was due to the condensation process in the lower atmosphere which resulted in increased aerosol particle sizes with higher scavenging rates of aerosols and low activity concentrations of ⁷Be in the atmosphere. Influence of precipitation on the changes of ⁷Be activity concentrations was also observed.     

Variation of 7Be concentration in surface air at Nagano, Japan

The concentration of ⁷Be in surface air at Nagano City has been measured during the period from August 2000 to March 2005. The average monthly concentrations of ⁷Be in surface air were in the range of 3.3–14 mBq/m³ with pronounced two peaks in spring and autumn. It took 30–40 hours to recover the ⁷Be concentrations observed before, once ⁷Be was washed out by wet precipitations. For a pronounced increase in the concentrations of ⁷Be found in winter, a low-pressure trough coming close to the Japanese Islands with high concentrations of ⁷Be is responsible under the characteristic distribution of atmospheric pressure around the Japanese Islands.     

Seasonal variation of 7Be deposition in Japan

Seasonal variations of ⁷Be deposition in regions throughout Japan (26°18'N-43°05'N, 127°54'E-141°27'E) were observed during the period of 1989-1995. The observation indicated that ⁷Be deposition peaked in spring all over Japan except in the inland central basin. However, spring peak was not always the annual maximum. Along the coastal side of the Japan Sea, especially around Hokuriku region, ⁷Be deposition was at its maximum in winter. In addition, September peak also was observed in some regions, which was presumably caused by high precipitation or blowing in of northern air stream. Variations were classified into 4 types according to meteorological factors and local geographical conditions: winter peak, double peaks (spring and September peaks), spring peak and non-peak. A correlation between ⁷Be deposition and precipitation was observed in winter.     

Seasonal variation and activity size distribution of <Superscript>7</Superscript>Be in ambient air

The seasonal variation of the ⁷Be activities in air and the size distribution of the ⁷Be aerosols were studied by using a continuous air sampler and a five stage cascade impactor. The mean monthly activity level of ⁷Be at the Korea Atomic Energy Research Institute (KAERI) site varied from 0.5 to 4.8 Bq·m⁻³ and revealed a seasonal variation, in which the ⁷Be activity levels were high in winter and low in summer. The mass size distribution showed a bi-modal distribution with a higher peak around 0.49 μm and a smaller peak between 3 μm and 7.2 μm. The activity median aerodynamic diameter (AMAD) decreased with increasing ambient ⁷Be concentrations. The mean residence times by using a mean growth rate of 0.004 μm·h⁻¹ were estimated to be 2.5–6.4 days. The AMAD has an increasing tendency with higher relative humidity. It seemed that the high humidity condition facilitated the growth of the aerosol, resulting in increased deposition rates of the aerosols and the low ⁷Be content in the surface air. The AMAD of the ⁷Be aerosols increased with an increasing temperature, but the temperature dependency of AMAD should be explained with geological and meteorological conditions.     

Temporal variation of 7Be fallout and its inventory in purple soil in the Three Gorges Reservoir region, China

The deposition flux of ⁷Be was measured in the range from 0.4 to 5.2 Bq m^?2 d^?1, with a mean value of 2.6 Bq m^?2 d^?1, during the period of May 31, 2009?CMay 31, 2010 in the Three Gorges Reservoir region, China. The low annual deposition flux of ⁷Be was probably due to the adsorption of ⁷Be within high altitude clouds and the Qinling-Daba Mountain??s barrier and blocking effects on the cold air during winter months. There was a seasonal trend for ⁷Be deposition, showing a spring maximum and winter minimum, which may be attributed to the seasonal folding of tropopause in spring and little rainfall amount in winter. A strong positive correlation (R ² = 0.67) between ⁷Be deposition flux and rainfall was observed. The depth distribution of ⁷Be in undisturbed purple soil profiles suggested that the nuclide was mainly distributed within the top 20.0 kg m^?2 (~1.5 cm) of soil in depth and the maximum concentration occurred at a depth of 3.0 kg m^?2 (~0.2 cm), then the concentration declined quickly and exponentially with depth. The seasonal inventories of ⁷Be in soils were consistent with the values calculated from the atmospheric fluxes, which shows a great potential for using ⁷Be as a tracer to assess soil redistribution in purple soil areas of China.     

Total deposition velocities and scavenging ratios of 7Be and 210Pb at Rokkasho, Japan

The atmospheric concentrations and deposition fluxes of ⁷Be and ²¹⁰Pb were observed biweekly in Rokkasho, Japan on the Pacific Ocean coast at the northern end of Honshu Island, from March 2000 to March 2006, to clarify their regional features. Seasonal variation pattern of atmospheric ⁷Be concentrations had double peaks, and that of ²¹⁰Pb had a single peak. Deposition fluxes of ⁷Be and ²¹⁰Pb showed the same patterns. The total deposition pattern of ⁷Be was similar to that commonly seen on the Pacific Ocean side of northern Honshu Island, while the pattern of ²¹⁰Pb was similar to that commonly seen on the Japan Sea side. The lack of high spine mountains windward in Rokkasho may be the cause of this ambiguity in the winter monsoon season. Total deposition velocities and scavenging ratios of ²¹⁰Pb were similar to those of ⁷Be from spring to fall, and showed that both nuclides had a similar removal process from the atmosphere. However, the scavenging ratios of ²¹⁰Pb were slightly larger than those of ⁷Be in winter, indicating different behaviors for both nuclides in the scavenging process. The scavenging ratios of both nuclides inversely correlated with precipitation rate, and the ratios in winter were larger than in the other seasons.     

Beryllium-7 in near-surface atmospheric aerosols in mid-latitude (40°N) city Beijing, China

A high-volume air sampler and a high-resolution gamma-ray spectrometer have been used to measure the activity of ⁷Be in near-surface atmospheric aerosols at sampling frequency of 3 days week for 1 year from August 2009 to July 2010 at Beijing in the mid-latitude region of East Asia monsoon. The measurements indicate that the average concentration of ⁷Be was 8.39 ± 0.49 mBq m^?3, which was significantly higher than values reported for other cities in the East Asia monsoon region and in the world during the same period. The maximum and minimum of the weekly means of ⁷Be concentration were observed in September and May, respectively. The ⁷Be concentrations varied in accordance with the monsoon phases. Low but frequent wet precipitation may have caused lower ⁷Be observed in July when southeasterly was prevailing. Higher seasonal mean of ⁷Be concentrations in autumn could be attributed to the abnormal atmospheric circulation in autumn 2009.     

An attempt to evaluate dry deposition velocity of airborne210Pb in a forest ecosystem

Atmospheric concentration and total (wet plus dry) and dry deposition of²¹⁰Pb and⁷Be have been measured at our laboratory in Ishikawa Prefecture in Japan which faced the Sea of Japan during 1993–1994. At the same time inventories of excess²¹⁰Pb in soil samples were measured from a mixed pine forest. On the basis of the data obtained, an attempt was made to evaluate the dry deposition velocity as a result of the interception by the canopies of airborne²¹⁰Pb in a pine stand The dry deposition velocity of²¹⁰Pb in the pine stand was roughly estimated to be 0.9–0.8 cm/s, higher by a factor of about 10 than the value (mean: 0.12±0.09 cm/s; range: 0.06–0.28 cm/s) in the open area measured on the roof of our laboratory.     

Atmospheric concentrations of 7Be and 210Pb in Granada, Spain

Aerosols samples in near-surface air of Granada (Spain) were collected on a weekly basis. The seasonal ²¹⁰Pb and ⁷Be concentrations were determined during the five-year period, from October 1993 to September 1997. The elements, despite their different origin and their different distribution throughout the atmosphere, present the same seasonal variation. There was a tendency for a maximum during the summer season and a minimum during fall and/or winter. In this work, the concentration of ⁷Be and ²¹⁰Pb and meteorological data have been used in order to determine the periods of the potential radioactive pollution. This study, also, shows that the deposition of ⁷Be occurs primarily by precipitation except during the investigation periods where precipitation was scarce and irregular.This revised version was published online in November 2005 with corrections to the Cover Date.     

Radionuclide variations in the air over Monaco

Radionuclides in aerosols and precipitation have been analyzed by IAEA-MEL in Monaco since 1987 and 1999, respectively, to identify their behavior in the atmosphere and delivery into the northwestern Mediterranean Sea. While the concentration of ⁷Be in aerosols has been affected by the stratospheric-tropospheric mixing and precipitation, the concentration of ¹³⁷Cs in aerosols has been influenced by a combination of local meteorological conditions and re-suspension of ¹³⁷Cs from soil. Higher concentrations of ⁷Be, ¹³⁷Cs, ^239,240Pu and ²⁴¹Am in precipitation occurred during spring and summer. The highest deposition rates of these radionuclides were observed in spring and autumn during periods of high precipitation. A good correlation was found between the amount of precipitation and depositional flux for ⁷Be, but not for ¹³⁷Cs, ^239,240Pu and ²⁴¹Am. This indicates that the wet process as well as the dry process seem to be important factors in determining the annual deposition for transuranic radionuclides and ¹³⁷Cs.     

Distribution and mean residence time of natural radionuclides in the forest ecosystem

Activity concentrations of radionuclides,⁷Be,²¹⁰Pb and²¹⁰Po, in precipitation (rain, throughfall and stemflow), wood and soil were determined by using gamma-ray and alpha-ray spectrometry to estimate the migration behavior of these radionuclides in the forest canopy. The activity ratios between output and input precipitations for the forest canopy were 0.53 of⁷Be, 0.79 of²¹⁰Pb and 1.5 of²¹⁰Po for Pasania edulis forest. A dynamic model of the transport and fate of radionuclides in the forest ecosystem was constructed. Mean residence times of radionuclides were 56 days for⁷Be, 765 days for²¹⁰Pb and 653 days for²¹⁰Po for Pasania edulis forest.     

Impact of the meteorological parameters on the behaviour of 7Be at ground level in Tetouan city,Morocco from June 2015 to February 2017

For the first time, atmospheric aerosols were collected in Tetouan city (Morocco), from June 2015 to February 2017, through which ⁷Be activity was measured. We studied data variation by time series analyses and the impact of local meteorological factors on it. ⁷Be concentrations, in mBq/m³, ranged from 1.65 to 7.79 with mean value of 4.69. ⁷Be behaviour is mainly influenced by air temperature, precipitations, relative humidity and atmospheric pressure. A prediction model was suggested and validated. This study helps understanding climatic variables impact on the environmental processes as aerosols transport and deposit, and to predict ⁷Be behaviour in Mediterranean regions like Tetouan.

     

Spatial distribution of 7Be in soils of Lower Austria after heavy rains

The ⁷Be approach in estimating the erosion rates is based on the assumption that the deposition of ⁷Be fallout associated with the erosive event is spatially uniform. The objective of the present work was to verify this assumption by assessing the influence of heavy rainfalls on the ⁷Be spatial distribution in Seibersdorf soils, Austria. Incremental and bulk soil depth profiles were collected from a flat site, undisturbed for the last 9 months prior sampling and with no evidence of erosion or deposition after the occurrence of heavy rains (>30 mm day^?1). The mean value of the ⁷Be areal activities (Bq m^?2) measured at 10 different points from the selected area was 312 Bq m^?2. This value corresponded to a total rainfall of 295 mm within the last 5 months prior sampling, considering that the highest mass activity of ⁷Be at soil surface will decay below the minimum detectable activity after 5 months’ time. The resulted coefficient of variation had a value of 19 % showing acceptable spatial variability of ⁷Be fallout connected with individual storm events on a local scale.     

Transfer of 7Be, 210Pb and 210Po in a forest canopy of Japanese cedar

The concentrations of ⁷Be, ²¹⁰Pb and ²¹⁰Po of ca. 60 parts of a whole tree of Japanese cedar and of underlying litter and soil samples were determined for studying their transfer in a forest canopy. The results suggest that the mean residence times of ⁷Be and ²¹⁰Pb in the forest canopy were ca. 20 and 900 days, respectively, and the dry deposition rate of ⁷Be on the forest canopy was about a half of the total deposition rate.     

Seasonal variation of natural radionuclides and some elements in plant leaves

Leaf and aerosol samples were monthly collected in Mt. Sefuri (Fukuoka Prefecture). Radioactivities of ⁷Be, ²¹⁰Pb and ⁴⁰K were determined with gamma-ray spectrometry. The concentrations of some elements in the leaf samples were determined by neutron activation analysis. Similar seasonal variation of ⁷Be and ²¹⁰Pb was observed between leaf and aerosol samples, high in spring and winter and low in summer. Correlation factors for trace elements contained in the leaf show large variations. This indicates that the contribution of two sources (atmospheric deposition and uptake from soil) is very variable.     

Characterisation of lead rhodizonate as barium and radium adsorber from fresh water

A series of metal -diketonates were irradiated with bremsstrahlung of maximum energy of 50 MeV and the recoil behavior of⁷Be, formed from¹²C of ligands through¹²C(, n)⁷Be reaction, was investigated.⁷Be nuclides thus formed were detected partially as central metal atoms of the complexes. Complex yields of⁷Be were compared and an anomalously high yield was observed in tris-acetylacetonatocobalt(III) [Co(acac)₃].     

Behavior of radiocesium in atmospheric arerosol and fallout in Prague

Radiocesium in ground layer atmospheric aerosol and fallout in Prague has been examined. After a decline in 1986–1988, controlled by a sum of two negative exponentials,¹³⁷Cs aerosol concentration reached a constant level based on an equilibrium between its deposition and resuspension. Deposition velocity was compared to that of⁷Be and²²⁶Ra. It confirmed the supposed source of¹³⁷Cs as resuspension from the ground. Resuspension factor of the order of magnitude of 10^–9 was determined, reminding similar values found earlier in Prague as well as those found in Munich. It also agrees well with the USAEC resuspension model. Solubility of¹³⁷Cs was measured in combined wet and dry fallout. The average undissolved fraction of¹³⁷Cs was found to be about 70% which can be explained by the conditions of the¹³⁷Cs aerosol formation in Chernobyl.