The reported levels of deposition are based on (i) airborne gamma surveys, (ii) in situ measurements of gamma spectrometry and (iii) measurements of soil samples of different depths. The latter has been determined by following the respective guidelines of the IAEA (1989). According to them, stones, and biological residues have been removed from the soil sample and the weight of the remaining is recorded. Then the sample is homogenized and dried (~100°C) until a constant weight. The sample is then sieved through a 2-mm sieve, and it is finally transferred to the optimal counting geometry for gamma spectrometry measurements.
Given that each research group has used a different sampling methodology and measurement technique (different detection systems), it is evident that the uncertainty of the results is different for each sample. For example, laboratory analyses of ground-based samples in general characterize the deposition at a location better than what is possible with airborne surveys. On the other hand, airborne gamma spectrometry provides a rapid and spatially representative result, but it is sensitive to the distribution of activity in the environment.
The improvement in the deposition of 137Cs comparing to the REM (Radioactivity Environmental Monitoring) can be seen below:
Sampling points of deposition observations of 137Cs all over Europe from the public REM database of the JRC.
It is noteworthy that the database lacks observations from the ex-Soviet Union countries where the actual deposition of the radioactive fallout took place following the initial releases of Chernobyl. Lower panel: The updated database, which now covers all the highly contaminated areas in Ukraine, Belarus and Russia.
The original database contains five different records; three for air activity concentrations of 131I, 134Cs and 137Cs formatted as below:
- SITE: station code;
- LON: longitude of sampling station;
- LAT: latitude of sampling station;
- STARTDATETIME: beginning date and time of sampling in a format year-month-dayThour:minuteZ;
- ENDDATETIME: ending date and time of sampling under the same format;
- VALUE: surface air activity concentrations (in Cs134_con, Cs137_con and I131_con) or deposition density (in Cs134_dep and Cs137_dep);
- UNIT: the respective unit (Bq m-3 for air concentration, Bq m-2 for deposition, kBq m-2 for deposition etc.).
and two for the total deposition of 134Cs and 137Cs under the same format. For each record, there is one self-describing ascii-file that includes extensive metadata and describes the measurements (Cs134_con, Cs137_con and I131_con for air activity concentration data and Cs134_dep and Cs137_dep for deposition density).
The data can be downloaded below after login.
We also store deposition data of 137Cs 90Sr, 238Pu, 239Pu, 240Pu and 241Am from the Chernobyl Exclusion Zone (CEZ) for year 2015. The data (N=48,781) were obtained in order to study the recent fires in the CEZ. They cover a small area inside the CEZ in which the fires of 2015 occurred. The range of the deposition fields for the aforementioned radionuclides is shown below: