Luminescence dosimetry for evaluation of the external exposure in Metlino, upper Techa River valley, Southern Urals, Russia: Analysis of new results
Introduction
The Mayak plutonium facility in the Southern Urals, Russia, discharged liquid radioactive waste into the nearby the Techa River in the years 1949–1956. As a result, residents of villages along the Techa River were exposed to significant levels of radiation via internal and external pathways. A follow-up of the ‘Extended Techa River Cohort’ (ETRC), comprising about 30,000 persons, over decades has revealed an elevated number of both leukemia and solid cancer cases (Kossenko et al., 2002). To be able to relate the excess cases to a radiation risk, a valid dosimetry system is needed, which was introduced by scientists of the Urals Research Center for Radiation Medicine (URCRM) as the Techa River Dosimetry System (TRDS; Degteva et al., 2000). Reconstruction of external doses in TRDS is based on measurements of gamma-dose rates in air at the shoreline and in living areas, which had been conducted starting from 1952 (Vorobiova et al., 1999). For the period of 1949–1951, in which the majority of the environmental contamination occurred, no such data is available, thus the dosimetry system relies on modelled radionuclide data. Validation of the model results with independent experimental methods is then an important aspect. One such possibility is to use ceramic building materials such as bricks and tiles as a dose archive in settlements, which can be readout with luminescence techniques to determine the absorbed dose in brick due to the environmental radioactive contamination. Previous studies have shown that this dose information can then be combined with radiation transport calculations to reconstruct the external gamma exposure (Hiller et al. 2017, 2022; Woda et al., 2011a; Göksu and Bailiff 2006; Göksu et al., 2006; Bailiff et al. 2004a, 2004b; Taranenko et al., 2003; Meckbach et al., 1996). In this work the methodology is used to validate the TRDS.
For the area of the Techa river, the highest external doses occurred in the former village of Metlino, which is the focus of the present study, and which is located 7 km downstream of the release point and was evacuated in 1956. Fig. 1 illustrates the evolution of the study site from the time when the village was intact and populated to today. Of the original houses and buildings, most were destroyed when the settlement was evacuated in 1956; only the parts of the old mill, granary and the church remain today. All are located close to the former Techa River shoreline and floodplains, the mill and granary are also close to the Metlinsky pond shoreline. After relocation of the residents, a reservoir lake was created, which significantly changed the exposure geometry. The former strong sources of shoreline and floodplain of the Techa River are now effectively shielded by a water column up to 3 m deep.
Previous dose reconstruction works in Metlino have used bricks from the south-western wall of the mill for evaluation of the air kerma at the blind creek of the Techa River, labelled (III) in Fig. 1 a (Taranenko et al. 2003, 2013; Jacob et al., 2003), bricks from the walls of the church tower for evaluation of the air kerma at the bank of the eastern most arm (I) of the Techa River (Hiller et al., 2017) and bricks from the north-western wall of the granary for evaluation of the air kerma at the shoreline of the Metlinsky Pond (Hiller et al., 2022; Woda et al., 2020). The other three walls of the granary have meanwhile collapsed, but before this happened, a number of brick samples were taken in the 1990s by URCRM and stored there. Dose information in these bricks could be used to derive air kerma values in between the Techa River arms and in this way investigate the homogeneity of exposure conditions of the former population of Metlino across the entire Techa River area. So far, however, only one brick sample per wall has been analysed and the measured dose reported (Degteva et al., 2008).
The aim of this study is to provide a more complete dataset of brick dose measurements of samples from the north-eastern and south-eastern wall of the granary, which can then be used for dose reconstruction. Particular challenges in the measurement protocols and background dose assessment for some of these samples are described and an overall evaluation of the quality of the dose results is given. The variation of the brick dose values along both walls is discussed on a qualitative basis, considering the state of knowledge on the exposure geometry before and after 1956. In addition, results of dose depth profiles for selected samples are presented, which give information about the source energy and to some extent also on the source geometry. This is illustrated by comparison of these profiles with the dose depth profiles of brick samples from the north-western wall of the granary, which faced the contaminated shoreline of the Metlinsky Pond (Hiller et al., 2022).
The results presented in this paper are part of a full-scale validation study of the TRDS 2016, which, apart from the luminescence measurements, includes photon transport calculations for derivation of anthropogenic doses in air at the river bank. Details and results of the latter aspect will be given elsewhere.
Section snippets
Sample collection and preparation
The brick samples were collected from the NE and SE wall of the granary during a sampling campaign in December 1996, when the ice thickness of the frozen reservoir lake was sufficient to allow accessing of the walls and sampling on foot. All samples were taken at a height of 1.5 m above ice (water level). At selected sample positions, the dose rate in front of the brick sample was measured with a hand held dose rate meter, in units of μR h−1. These values were converted here to μGy h−1 by
Luminescence properties and measurement protocol
Samples 37, 42, 43 and 47 showed favourable properties in OSL: a strong fast component and negligible sensitivity changes when applying a 190° preheat. Obviously in this context, the quartz dosimetric system behaves as if it were in the most simple state of a one trap/one center model. This gives high confidence in the obtained results. An example of this type of behaviour is given in the upper panel of Fig. 3. In these cases, the measurement procedure also resulted in homogeneous, narrow dose
Summary and conclusions
Several bricks from the NE and SE exposed walls of the granary in Metlino, facing the Techa River were sampled and the anthropogenic dose measured in several depth intervals for the purpose of dose reconstruction. The majority of samples showed favourable properties in OSL but in some cases significant levels of signal recuperation where observed which made adjustments in the measurement protocols necessary. Tentative dose measurements using the isothermal TL readout at 190 °C for one sample
CRediT authorship contribution statement
C. Woda: Writing – original draft, Methodology, Investigation, Funding acquisition, Formal analysis, Conceptualization. M. Hiller: Writing – review & editing, Investigation, Funding acquisition. J.A. Ademola: Writing – review & editing, Methodology, Investigation, Formal analysis. N.G. Bugrov: Writing – review & editing, Methodology, Investigation, Conceptualization. M.O. Degteva: Writing – review & editing, Investigation, Funding acquisition, Formal analysis, Conceptualization. B. Napier:
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The research leading to these results has received funding from the European Community's Seventh Framework Program (FP7/2007–2013) under grant agreement n°249675 and from the Russian Health Studies Program of the U.S. Department of Energy (DOE) under the auspices of the Joint Coordinating Committee for Radiation Effects Research Project 1.1, Techa River Population Dosimetry. J.A. Ademola acknowledges the Alexander von Humboldt Foundation, Germany, for the fellowship awarded that enabled the
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