Monitoring of radiation in the atmosphere and a food chain. Results in the Netherlands in 1993
Metingen van radioactiviteit in de atmosfeer en een voedselketen. Resltaten voor Nederland in 1993
RIVM Report 610056011
This 1993 annual report presents the results of biosphere sample measurements by the Laboratory of Radiation Research (LSO) of the National Institute of Public Health and Environmental Protection (RIVM). The measurements are part of the National Measurement Programme (NMP) of the Coordinating Committee for the Monitoring of Radioactive and Xenobiotic Substances (CCRX) in the Netherlands. The NMP is considered essential for an adequate assessment of radioactivity in the biosphere. The programme of the RIVM/LSO includes samples of airdust and deposition taken at the RIVM premises in Bilthoven. Samples of grass and milk were taken from the surroundings of nuclear installations in the Netherlands and on Dutch territory in the vicinity of such installations situated abroad. An overall country milk sample from four milk factories in the Netherlands was also analyzed. This report also presents the data of the National Radioactivity Monitoring Network (LMR) in 1993. These data are not included in the NMP. In 1993, the yearly average gross alpha- and gross beta-activity concentration of airdust was 0.09 +- 0.01 (SD 0.04) and 0.55 +- 0.04 (SD 0.37) mBq.m-3, respectively. These values were significantly higher than those of previous years. This effect is explained by a change in the procedures for sample taking and sample treatment. The gamma-spectrometric analysis was performed on airdust sampled with a high volume sampler. For Be-7, Cs-137 and Pb-210 the yearly average of the activity concentrations were 3600 +- 50 (SD 1300), 1.7 +- 0.1 (SD 1.3) and 530 +- 10 (SD 500) muBq.m-3, respectively (well detector results). The yearly total gross alpha- and gross beta-activity of the deposition in Bilthoven was 54.3 +- 0.7 and 87.9 +- 0.8 Bq.m-2, respectively, and the deposition of H-3 was 1310 +- 30 Bqm-2. The total activity of Cs-137 in deposition was 0.80 +- 0.03 Bq.m-2, of Pb-210 105 +- 2 Bq.m-2 and Po-210 6.0 +- 0.6 Bq.m-2 (alpha-spectroscopy). These activities are comparable to those of previous years. The yearly average concentrations of Cs-137 and Sr-90 in consumer milk from a nationwide sample mix was 0.09 +- 0.02 and 0.04 +- 0.01 Bq.L-1, respectively, which are about equal to that of the previous year. For the gross alpha-activity concentration, as measured by the aerosol monitors of the LMR, values in the range of 0.3 - 12.1 Bq.m-3 were found (5-percentile - 95-percentile values), with an average value across the country of 2.6 Bq.m-3. This value corresponds to the value of 2.4 Bq.m-3 in 1992. No 'man-made' beta-activity was measured with the LMR monitors. The dose-equivalent rate measured with the LMR monitors was in the range of 54.5 - 95.3 nSv.h-1 (5 percentile - 95 percentile values). The average value of 77.3 nSv.h-1 was in good agreement with the 1992 and 1991 averages (79.3 and 78.9 nSv.h-1, respectively).