MONITORING 241Pu IN UKRAINIAN SOIL

We collected ca. 500 soil samples from within the inhabited territory of the Ukraine for 241Pu determination. To cover the expected wide range of contamination levels due to fallout from the Chernobyl Nuclear Power Plant (NPP) accident, we took samples in the following regions: Kiev (170 samples), Gitomir (70 samples), Chernigov (60 samples), Rovno (70 samples), other regions (130 samples). We used 10 g of soil from a 5-cm depth coring cylinder. We ashed the samples for 4 h at 400°C and then used a mixture of HCl and HF followed by HNO3 to solubilize the plutonium. We stabilized the plutonium with NaNO3 and isolated it using Dowex-1 ion exchange resin. Finally, we deposited the plutonium electrochemically onto stainless steel disks. We determined the activities of the a-emitting isotopes of plutonium, including the 242Pu yield tracer, using traditional a-spectroscopy systems. Our chemical yields were typically 40-80%. We used liquid scintillation counting (LSC) for the determination of the 1Pu activity on each disk. Our method employs an ultra low-level a/3 spectrometer (Quantulus 1220TM), 7-ml aluminium/Teflon® vials and a highlight output, toluene based liquid scintillation cocktail (GS-1). The analytical parameters were: counting efficiency =15%, background count rate = 0.55 cpm, figure of merit (E21 B) = 409, minimum detectable activity (MDA) for 120 min count = 2.3 Bq kg-1 and the MDA for a 500 min count =1.0 Bq kg-1. Geometric mean values and standard deviations for 1Pu activities in soil from the inhabited regions which were studied were 20.5±i2.9 Bq kg-1