Evaluation of anthropogenic dose distribution amongst building walls at the Metlino area of the upper Techa River region.

This paper presents the results of an effort to evaluate anthropogenic doses in bricks from old buildings located on the banks of the Techa River. The river area was contaminated in 1949-1956 as a result of radioactive waste releases by the Mayak plutonium facility (Southern Urals, Russia). Absorbed doses were determined by luminescence measurements of quartz extracted from the near-surface layers of bricks sampled in 1991-1997 from three remained buildings (a mill, a granary and a church). These buildings are located in the former residence area of Metlino, which was the settlement located closest to the release site (residents of Metlino were relocated from the contaminated river in 1956). The measured anthropogenic dose in the three buildings was found to be comparable: minimum values were equal to 0.5-0.9 Gy and maximum values amounted to about 3-4 Gy. Unfortunately, the geometry of gamma-exposure of the brick samples changed significantly in 1956 as a result of creation of an artificial reservoir downstream of the Metlinsky pond. Since luminescence data provide absorbed dose in the investigated samples accumulated over the whole period of irradiation, for interpretation of the data obtained it is important to know the exposure geometry for the period of maximal exposure, which was in the early 1950s. In 2005, archival data describing configuration of contaminated water streams and shorelines (which were the main sources of gamma-irradiation) were published. Comparison of these data with the results of the luminescence study presented here showed that the bricks with the highest thermoluminescence (TL)-based doses faced contaminated shores and were located close to them. In contrast, the bricks with lower values of measured dose were opposite to contaminated shores and/or being shielded. This demonstrates that the luminescence method allowed reconstruction of the anthropogenic dose distribution in the former settlement center. The obtained results suggest new options for further luminescence studies in Metlino aimed at the reconstruction of the external exposures of the affected population.