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Pu and U atom ratios and concentration factors in reservoir 11 and Asanov Swamp, Mayak PA: an application of accelerator mass spectrometry.

Mayak Production Association, East Ural, Russia, was established to produce weapons-grade plutonium. Routine discharges and accidents at Mayak PA contaminated large areas, including the Techa River. The objectives of the present work were to study atom ratios for plutonium and, for the first time to our knowledge, uranium isotopes in water, soil, grass, and aquatic biota samples from Reservoir 11 and the Asanov Swamp, downstream from Mayak PA. Atom ratios (240Pu/239Pu, 236U/235U, 235U/238U) were determined using accelerator mass spectrometry to confirm radionuclide source characteristics and calculate activities and concentration factors for the studied samples. The lowest 240Pu/239Pu atom ratios were consistently found in Asanov Swamp samples (approximately 0.019), indicating a major contribution from early discharges of weapons-grade Pu. 240Pu/239Pu atom ratios in Reservoir 11 were higher, indicating influence from more recent civil reprocessing. The presence of 236U is usually indicative of fuel irradiation; 236U/235U ratios increase from weapons to civil sources. Our new data show that Asanov samples had lower 236U/ 235U ratios than Reservoir 11 samples (0.0005-0.0045 for Asanov compared with 0.0074-0.0153 for Reservoir 11) in agreement with Pu results. Pu and U concentration factors calculated for vegetation and biota samples at Mayak were comparable with corresponding values found in the literature.