title: Artificial radionuclides in surface air in Finland following the Fukushima Dai-ichi nuclear power plant accident.
abstract: We present observations of radionuclides released during the Fukushima Dai-ichi nuclear power plant accident in ambient air and in deposition made in Finland during March-May 2011. The first observed fission product was (131)I, which arrived in Finland 8-9 days after the accident. Detections of (137)Cs and (134)Cs were made 2-3 days after the first (131)I observations. The highest concentrations of fission products in Finland were observed during March 31st and April 1st. The highest observed concentrations of the following isotopes were: (131)I (10.6 ± 0.4 mBq/m(3)), (134)Cs (0.397 ± 0.020 mBq/m(3)), (137)Cs (0.405 ± 0.017 mBq/m(3)), (136)Cs (28 ± 2 μBq/m(3)), (129)Te (129 ± 9 μBq/m(3)), (129m)Te (234 ± 20 μBq/m(3)), (132)Te (51 ± 3 μBq/m(3)) and (132)I (54 ± 3 μBq/m(3)). Generally, higher concentrations of fission product were observed in Southern Finland than in Northern Finland. The variations in the (137)Cs and (134)Cs activity concentration data suggest that three separate plumes passed over Finland with decreasing concentrations. The first plume, with highest cesium concentrations, passed over Finland during March 31st - April 2nd, the second plume during April 4th - 6th and the third and smallest one during April 10th - April 11th. Both aerosol and gaseous iodine fractions were sampled simultaneously and thus an accurate view of the behaviour of aerosol and gaseous fractions was obtained. Large variations between different fractions were observed with the gaseous fraction representing 65-98% of the total (131)I. The (134)Cs/(137)Cs ratio was determined to be 0.99 ± 0.10, which indicates a fuel burnup of approximately 30 MWd/t. The (136)Cs/(137)Cs and (129m)Te/(132)Te ratios were used to estimate the time lapse after the accident. The differences between true time lapse and the ones deduced from the isotope ratios were from the correct time lapse to 0-3 days for (136)Cs/(137)Cs and 5 days for (129m)Te/(132)Te, respectively. Radionuclides from the Fukuhisma Dai-ichi nuclear power plant were also observed in deposition samples. In Norther Finland, the total deposition of 0.28-0.62 Bq/m(2) for (137)Cs and 0.21-0.57 Bq/m(2) for (134)Cs was determined during March-May 2011. For (131)I the deposition of 8.5 ± 2.9 Bq/m(2) was determined at Rovaniemi from the samples from the sample collected during April 1st - 12th.
authors.affiliation: Radiation and Nuclear Safety Authority - STUK, Lähteentie 2, FIN-96400 Rovaniemi, Finland. Electronic address: ari.leppanen@stuk.fi.
authors.forename: Ari-Pekka
authors.initials: AP
authors.lastname: Leppänen
authors.forename: Aleksi
authors.initials: A
authors.lastname: Mattila
authors.forename: Markku
authors.initials: M
authors.lastname: Kettunen
authors.forename: Riitta
authors.initials: R
authors.lastname: Kontro
mesh_terms: D000396:Air Pollutants, Radioactive / Q000032:analysis*; D002588:Cesium Radioisotopes / Q000032:analysis; D005387:Finland; D062406:Fukushima Nuclear Accident; D007457:Iodine Radioisotopes / Q000032:analysis; D011868:Radioisotopes / Q000032:analysis*; D013691:Tellurium / Q000032:analysis
chemical_list: D000396:Air Pollutants, Radioactive; D002588:Cesium Radioisotopes; D007457:Iodine Radioisotopes; D011868:Radioisotopes; D013691:Tellurium
keywords: Airborne radioactivity; Deposition; Finland; Fukushima; Isotope ratio