Onderzoek naar de radioactiviteit van depositie. Resultaten over 1990

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This report presents the results of measurements of radionuclides deposited in the Netherlands (Bilthoven) in 1990. Measurements were carried out to determine the weekly activities of gamma-emitters, of H-3 (on a weekly basis) and of Pb-210 and Po-210 (on a monthly basis). The gross alpha, gross beta and gross gamma-activity were also determined on a weekly basis. The yearly average concentration of H-3 in rain was 1.8 +- 0.2 kBq/m3, lower than in 1989. The total deposition of H-3 was 1360 +- 120 Bq/m2, which is lower than in the period 1985 - 1989. The total deposition of Be-7 was 810 +- 36 Bq/m2, slightly higher than in 1989. The weekly deposition of Cs-134 was always below the detection limit of 0.05 Bq/m2. The total activity of Cs-137 in deposition was less than 5.5 Bq/m2. The total depositions of the natural radionuclides Pb-210 and Po-210 were 85 +- 4 Bq/m2 respectively 16 +- 2 Bq/m2. These values are below those found in 1989. In 1990 the gross alpha-activity in deposition was 68 +- 1 Bq/m2, which is slightly higher than in previous years. The gross beta-activity in deposition was 121 +- 4 Bq/m2, which is also higher than the value found in 1989. The gross gamma-activity was 109 +- 4 Bq/m2. This was lower than in the years 1985 - 1989.