Resumen
The integration of the radioactivity spectrometer KATERINA II in a fixed station (buoy) of the POSEIDON network at the North Aegean Sea within the framework of MARRE Project is presented. The acquisition period lasted from 20 November 2019 till 22 February 2020. An intense increment of the activity concentration of radon progenies (up to an order of magnitude) was recorded during rainfall. More specifically, the 214Bi activity concentration varied from 0.09 to 0.53 Bq L-1 without rainfall and the 214Pb activity concentration varied from 0.14 to 0.81 Bq L-1. The 214Bi activity concentration during rainfall ranged from 0.4 to 5.4 Bq L-1 and of 214Pb from 0.3 to 5.3 Bq L-1. The minimum detectable activity of the KATERINA II detection system for measuring low level activities of 137Cs is optimized applying background subtraction and the full spectrum analysis technique.