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タグ「7Be (Beryllium)」

Atmospheric deposition of cosmogenic 7Be and 137Cs from fallout of the Chernobyl accident

ecology・environment

Title: Atmospheric deposition of cosmogenic 7Be and 137Cs from fallout of the Chernobyl accident

Author: C. Papastefanou, A. Ioannidou, S. Stoulos, M. Manolopoulou

Reference: Science of The Total Environment, Volume 170, Issues 1–2, 18 August 1995, Pages 151-156

DOI: http://dx.doi.org/10.1016/0048-9697(95)04608-4

Keywords: Atmospheric depositional flux; Cosmogenic radionuclides; Chernobyl accident

Abstract: Atmospheric (tropospheric) depositional fluxes of the naturally occurring 7Be of cosmogenic origin and 137Cs from fallout of the Chernobyl accident were measured over a 7-year period (January 1987–December 1993) at Thessaloniki, Greece (40° 38′N, 22° 58′E). The annual total deposition fluxes of 7Be varied between 854 Bq/m2 (1987) and 1242 Bq/m2 (1992), showing a minimum in the years 1988–1989. The annual total deposition fluxes of 137Cs varied between 183 Bq/m2 (1987) and 16.4 Bq/m2 (1992), showing a significant decrease as expected for natural removal and radioactive decay and no new releases from nuclear facilities or weapons testing. The annual average total deposition velocity for 7Be was from 0.3 cm/s (1988) up to 0.8 cm/s (1991), while for 137Cs the corresponding values were much higher, hence 137Cs was associated with larger atmospheric particles. High 7Be concentrations in air were related to the very little solar activity (1987–1988 and 1993–1994), while low 7Be concentrations in air related to the high solar activity (1989–1991). Maximum 137Cs concentrations in air were registered during the spring 1991 and 1992, reflecting some stratospheric inputs. An unusual highly elevated value of 137Cs concentration in air, reaching 0.25 mBg/m3, was observed during the summer 1990.

URL: http://www.sciencedirect.com/science/article/pii/0048969795046084

Seasonal 7Be and 137Cs activities in surface air before and after the Chernobyl event

ecology・environment

Title: Seasonal 7Be and 137Cs activities in surface air before and after the Chernobyl event

Author: A. Kulan

Reference: Journal of Environmental Radioactivity, Volume 90, Issue 2, 2006, Pages 140-150

DOI: http://dx.doi.org/10.1016/j.jenvrad.2006.06.010

Keywords: 7Be; 137Cs; Atmosphere; Aerosols; Chernobyl fallout; Nuclear weapons fallout; Sweden; Europe

Abstract: Seasonal fluctuations of cosmogenic 7Be (T1/2 = 53.4 days) and anthropogenic 137Cs (T1/2 = 30 years) activities in surface air (aerosols) have been extracted from a long data record (1972–2000) at high latitude (56°N–68°N, Sweden). Normalization to weekly average values was used to control long-term trends so that cyclical trends could be investigated. Enhanced 7Be activity was observed in spring and summer seasons and likely relates to the seasonal thinning of the tropopause. Variations in the 137Cs activity record seem to reflect how the isotope was injected in the atmosphere (stratospheric from bomb tests and tropospheric from the Chernobyl accident) and subsequent transport mechanisms. Accordingly, until 1986, the surface air 137Cs activity was strongly related to nuclear weapons test fallout and exhibits temporal fluctuations resembling the 7Be. Conversely, since 1986 the Chernobyl-produced 137Cs dominates the long-term record that shows annual cycles that are strongly controlled by atmospheric boundary layer conditions. Additionally, short-term data within the post-Chernobyl period suggest subtle intrusion of air masses rich in 137Cs that may occur throughout the year, and differences resulting from spatial occurrence at these latitudes. This is an important observation that may have to do with year-to-year variation and calls for caution when interpreting short-term data records.

URL: http://www.sciencedirect.com/science/article/pii/S0265931X06001032

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