Radionuclides in the ground-level atmosphere in Vilnius, Lithuania, in March 2011, detected by gamma-ray spectrometry

Abstract This study presents the ground-level air monitoring results obtained in Vilnius, the capital of Lithuania, on 14 March–14 April 2011 after the recent earthquake and subsequent Tsunami having a crucial impact on Japanese nuclear reactors at the Fukushima Daiichi Nuclear Power Plant (NPP) on 11 March 2011. To collect representative diurnal aerosol samples a powerful sampling system ensuring the air filtration rate of 5500 m 3  h −1 was used. The following artificial gamma-ray emitting radionuclides have been determined: 129m Te, 132 Te (in equilibrium with its daughter 132 I), 131 I, 134 Cs, 136 Cs and 137 Cs. Activity concentration of the globally distributed fission product 137 Cs has increased from a background value of 1.6 μBq m −3 to the value of 0.9 mBq m −3 at the beginning of April. The activity ratio 134 Cs/ 137 Cs was found to be close to 1, with a slightly higher activity of 134 Cs. The maximum aerosol-associated 131 I activity concentration of 3.45 mBq m −3 was by four orders of magnitude lower than that measured at the same location in April–May 1986 as a consequence of the Chernobyl NPP accident. The estimated gaseous fraction of iodine-131 constituted about 70% of the total 131 I activity.