Dose reconstruction in the contaminated area of the Techa river, Southern Urals, Russia.

We report on results of OSL and TL (210°C peak) measurements on quartz extracted from bricks from a mill in a contaminated village (Muslyumovo) of the Techa river valley, Southern Urals, for the purpose of dose reconstruction. The study has been carried out within the framework of EC funded project SOUL (‘Southern Urals Radiation Risk Research’). Previous works (Göksu et al. 2002) have shown that the expected dose due to man-made sources of radiation in the bricks is in the same range as the background dose due to natural sources of radiation, therefore a precise estimate of the cumulative and background dose is of utmost importance. The cumulative doses measured with TL are continuously lower (on average 10-20%) than the ones measured with OSL for the same sample and using the same luminescence reader. From dose recovery tests, laboratory kinetic analysis and available meteorological parameters of the sample site for the past 100 years, it is concluded that the most likely reason for the discrepancy is thermal fading of the 210°C TL peak. The background dose was carefully assessed by a combination of laboratory measurements, in-situ gamma spectrometry and Monte Carlo modelling. The results show that the background dose was overestimated in previous studies. The obtained anthropogenic doses in brick measured with OSL show variability within error limits between adjacent bricks and a distinctive height profile, which is supported by monitoring of the present day gamma dose rate using Al2O3:C detectors. Preliminary results of reconstruction of the external exposure of the population using the OSL measurements and computational modelling will be discussed

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

Luminescence dosimetry in a contaminated settlement of the Techa River valley, Southern Urals, Russia.

Optically stimulated luminescence (OSL) dosimetry is applied to quartz extracted from bricks from a mill in a contaminated village (Muslyumovo) of the Techa River valley, Southern Urals, Russia, for the purpose of dose reconstruction. Previous works [Goksu et al., 2002. First international intercomparison of luminescence techniques using samples from the Techa river valley. Health Phys. 82, 94-101] have shown that the expected dose due to man-made sources of radiation in the bricks is in the same range as the background dose due to natural sources of radiation, therefore a precise estimate of the cumulative and background dose is of utmost importance. Cumulative doses could be assessed with OSL with a precision of around 4% and lie between 450 and 600 mGy. The background dose was carefully determined by a combination of laboratory measurements, in-situ gamma spectrometry and Monte Carlo modelling. The results show that the gamma-dose rate of the soil was overestimated and the fractional brick gamma-dose rate underestimated in previous studies, but that the overall gamma-dose rate was nearly correct, due to mutual compensation. The obtained anthropogenic doses in brick measured with OSL lie between 200 and 300 mGy, show variability between adjacent bricks within error limits for one spot but a significant difference for two samples is observed for another spot. A distinct dependency of measured dose upon sample height is observed, which is an indication of a source distribution, which extends over a large area and up to a certain depth into the soil and in which higher contaminated areas are located at a greater distance to the mill than lower contaminated areas. A measured dose depth profile is compared with previously published Monte Carlo calculations to verify the source energy

Potential and limitations of the 210° C TL peak in quartz for retrospective dosimetry.

The potential of the 210 degrees C Thermoluminescence (TL) peak in quartz for accurate dose reconstruction is studied by comparative TL and optically simulated luminescence (OSL) measurements on quartz extracted from bricks from a mill in a contaminated village of the Techa River valley, Southern Urals, Russia. The cumulative doses measured with TL were found to be continuously lower (on average 10 -20%) than the ones measured with OSL for the same sample and using the same luminescence reader From dose recovery tests, laboratory kinetic analysis and available meteorological parameters of the sample site for the past 100 years, it is concluded that the most likely reason for the discrepancy is thermal fading of the 210 degrees C TL peak. By applying a suitable model, an effective lifetime of the electron trap of the 210 degrees C TL peak of 200-700 years is estimated for the moderate continental climate at the sample site. It is concluded that for samples in regions of continental climate and directly exposed to sunlight, dose measurements using the 210 degrees C TL peak should be restricted to the last 50-60 years. Applications to older samples should only be considered if bricks are not directly exposed to sunlight or if the background dose is small compared to the anthropogenic dose, as the latter will have been acquired during shorter times and will thus not have been subjected to significant thermal fading

External dose reconstruction for the former village of Metlino (Techa River, Russia) based on environmental surveys, luminescence measurements, and radiation transport modelling.

In the first years of its operation, the Mayak Production Association, a facility part of the Soviet nuclear weapons program in the Southern Urals, Russia, discharged large amounts of radioactively contaminated effluent into the nearby Techa River, thus exposing the people living at this river to external and internal radiations. The Techa River Cohort is a cohort intensely studied in epidemiology to investigate the correlation between low-dose radiation and health effects on humans. For the individuals in the cohort, the Techa River Dosimetry System describes the accumulated dose in human organs and tissues. In particular, organ doses from external exposure are derived from estimates of dose rate in air on the Techa River banks which were estimated from measurements and Monte Carlo modelling. Individual doses are calculated in accordance with historical records of individuals' residence histories, observational data of typical lifestyles for different age groups, and age-dependent conversion factors from air kerma to organ dose. The work here describes an experimentally independent assessment of the key input parameter of the dosimetry system, the integral air kerma, for the former village of Metlino, upper Techa River region. The aim of this work was thus to validate the Techa River Dosimetry System for the location of Metlino in an independent approach. Dose reconstruction based on dose measurements in bricks from a church tower and Monte Carlo calculations was used to model the historic air kerma accumulated in the time from 1949 to 1956 at the shoreline of the Techa River in Metlino. Main issues are caused by a change in the landscape after the evacuation of the village in 1956. Based on measurements and published information and data, two separate models for the historic pre-evacuation geometry and for the current geometry of Metlino were created. Using both models, a value for the air kerma was reconstructed, which agrees with that obtained in the Techa River Dosimetry System within a factor of two