RESUMEN
The radiation status of the national park (NP) Djerdap (Eastern Serbia) is characterized using bioindicators (mosses). Mosses (16 species, 156 samples) were collected randomly within the area of NP Djerdap during the month of June, periodically from 2015 to 2019. Samples were collected in the regions of Dobra, Donji Milanovac, and Tekija. Within the mosses, the presence of 40 K and 137Cs is regarded as a good indicator of radionuclides present in the environment due to their easy interchangeability with 39 K highly present in living moss organisms. The activity concentrations of gamma ray-emmiting radionuclides in samples were determined using high-resolution gamma ray spectrometry, an HPGe-ORTEC/Ametek detector. The determining activity concentrations of 40 K and 137Cs in collected samples were as follows: for 40 K from 31.4 to 721 Bq kg-1and for 137Cs varied from 2.6 to 908 Bq kg-1. The average activity concentrations of 40 K and 137Cs (Bq kg-1) in mosses in the period 2015-2019 were the lowest in moss samples collected in the Dobra region, and the highest in the area of Donji Milanovac. The most prevalent collected moss species within the Djerdap National Park was Hypnum cupressiforme. The determined activity concentrations in H. cupressiforme of 137Cs for the whole region of NP Djerdap for all 5 years was 78.1 ± 70.3 Bq kg-1 and of 40 K was 181 ± 86.1 Bq kg-1.