Milieurapportage 1993. IV. Monitoring of radiation in the atmosphere and a food chain. Results in the Netherlands in 1992

This 1992 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. Contrary to previous years measurements of radioactivity concentrations in surface- and sea water samples were not performed. 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 analysed. This report also presents information concerning the operationality and the data of the National Radioactivity Monitoring Network (LMR) in 1992. These data are not included in the NMP. In 1992, the yearly average gross alpha-and gross beta-activity concentration of airdust was 0.06 +- 0.01 and 0.44 +- 0.06 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 aerosol monitors of the LMR had an average availability of 88% in 1992, which is an improvement over the value of 76% in 1991. In 1992, just as in previous years, some structural monitor failures reduced the availability. The proportional counters were almost free of failures ; the average monitor availability was 96%, which is also an improvement compared to the 92% of the year before.