Vet er i nary Med i cine, Uni ver sity of Bel grade, Bel grade, Ser bia 2 Lab o ra tory for En vi ron men tal and Ra di a tion Pro tec tion, Vin~a In sti tute of Nu clear Sci ences, Uni ver sity of Bel grade, Bel grade, Ser bia 3 In sti tute of Me te o rol ogy, Fac ulty of Phys ics, Uni ver sity of Bel grade, Bel grade, Ser bia Sci en tific pa per Ac tiv i ties of 7 Be and 210 Pb were mon i tored in sur face air in Bel grade, Ser bia, from 2004 to 2012. The mea sure ments were taken from two lo

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... ca tions, in an open field of a city sub urb and in the cen tral city area. The ac tiv i ties were de ter mined on HPGe de tec tors by stan dard gamma spec trom e try. The 7 Be ac tiv ity shows a pro nounced sea sonal pat tern, with the max i mum in spring-sum mer and min i mum in win ter, while the 210 Pb ac tiv ity ex hib its two max ima, in autumn and late win ter. The mean monthly con cen tra tions mea sured at both sites are be low 9 mBq/m 3 and 1.3 mBq/m 3 for 7 Be and 210 Pb, re spec tively. The ob tained cor re la tion of the 7 Be ac tiv ity with the num ber of sun-spots is not sta tis ti cally sig nif i cant. Re la tions of the radionuclides' ac tiv i ties with cli mate vari ables (pre cip i ta tion, tem per a ture, rel a tive hu mid ity, cloud cover, sun shine hours, and at mo spheric pres sure) are also in ves ti gated, but the only signif i cant cor re la tions are found for the 7 Be ac tiv ity with tem per a ture and sun shine hours, and the 210 Pb ac tiv ity with at mo spheric pres sure. The max i mum 7 Be and 210 Pb ac tiv i ties cor respond ing to binned to tal monthly pre cip i ta tion data im ply dif fer ent modes of the radionuclide scav eng ing from the at mo sphere. Dur ing dry pe ri ods, ac cu mu la tion of the radionuclides in the at mo sphere leads to their in creased ac tiv i ties, but no cor re la tion was found be tween the ac tiv i ties and the num ber of con sec u tive dry days. Key words: ra dio ac tiv ity, be ryl lium-7, lead-210, air, sun-spot num ber, cli mate vari able J. V. Ajti}, et al.: A Multi-Year Study of Ra dio ac tiv ity in Sur face Air and Its .