The main objective of subproject 3 is to improve the quality of dosimetric data for members of the Extended Techa River Cohort (ETRC) and Extended Techa River Offspring Cohort (ETROC), in order to quantify better the risks associated with combined protracted exposures to strontium and external radiation. This objective will be achieved by:

·            Validation and verification of external dose estimates by the comparison of modelling-based doses for selected individuals and/or sites with the results of several independent dosimetry methods including: electron paramagnetic resonance (EPR) measurements of teeth (WP3.1) by taking into account contributions of incorporated strontium to the enamel dose (WP3.5); luminescence measurements of bricks that were sampled at sites where the people have been exposed (WP3.2); and (WP3.4) fluorescence in-situ hybridisation (FISH) measurements of chromosomal aberrations in lymphocytes (feasibility study of FISH to be completed by month 18, and full-scale validation study to be completed by month 48);

·            Implementation of the improved models of internal dose estimates for persons of different ages and genders with an emphasis on the biokinetic and dosimetric modelling of strontium for the foetus and infant (WP3.3); which is especially important for ETROC dosimetry (to be completed by month 48);

·            Amendment of individual dose estimates for the ETRC and ETROC members (WP3.6) by the use of the improved version of the Techa River Dosimetry System – 2006 (TRDS-2006), supplemented by special modules for fetal dose assessments and by the use of updated follow-up results (to be completed by month 36).

·            Further evaluation of the uncertainty in the final dose estimates (WP3.6) and creating the basis for future dosimetry system (to be completed by month 48).

In the second part of the project, the main deliverable will be the improved dosimetric database Techa-Doses 2008 (completion in month 36) associated with the epidemiological databases which will provide a basis for risk analysis.

 Subproject 3 Dosimetry for the extended Techa River cohorts consists of five work packages. Two workpackages (3.1 and 3.2) supported by the results of WP3.4 will provide the basis for external dose validation. WP3.1 will apply EPR on teeth to determine the external dose of selected individuals. In WP3.1 the EPR spectroscopy is combined with results of WP3.4 on dose contributions by strontium in order to improve the accuracy of EPR-based external doses. In WP3.2 gamma dose values at selected sites at the Techa River are determined by luminescence measurements of building materials and photon transport calculations. WP3.3 on internal dosimetry will provide improved models for fetal and infant dose calculation in ETROC including the pathway of breast feeding. The focus of WP3.5 will be on the integration of data and the incorporation of the achievements obtained during the first phase of project into a new version of the Techa River Dosimetry System (TRDS-2006), as well as on individual dose calculations for all members of ETRC and ETROC which will be fixed in database Techa-Doses 2008.

 Estimated strontium contributions of enamel dose will be used to improve EPR-based external doses both for Techa residents (WP3.1) and for Mayak workers (WP1.1). Evaluated individual external doses (WP3.1) and gamma dose values of Techa River sites (WP3.2) are inputs to WP3.6 for improvements and validation of external dosimetry modules in TRDS-2006. Dose coefficient estimates for the foetus and infant (WP3.3) represent the basis for internal dose calculation in ETROC (WP3.5). WP3.5 is the link between SP 3 dealing with dosimetry and SP 4 dealing with the improvement of follow-up data and risk analysis in the Techa cohorts.

WP3.1 Evaluation of the Techa River dosimetry system with EPR measurements of human teeth

Workpackage Leaders: Marina Degteva (URCRM),  Paola Fattibene(ISS)

 Recent measurements of absorbed doses in tooth enamel by EPR have demonstrated that these measurements can be applied for dosimetry for the Techa River population exposed to low-level radiation. New state-of-the-art technology is available at GSF and ISS that improves the sensitivity of the EPR method. Teeth extracted for reasons of dental health care are available at the URCRM tissue bank that includes over 3,000 samples from exposed and background donors. The status of each tooth and its donor has been documented in a special database. Preliminary EPR studies of the Techa River residents have shown that absorbed dose in enamel is induced by three main sources: external gamma exposure, beta particles of ⁹⁰Sr/⁹⁰Y incorporated in dental tissues, and background radiation. The enamel dose that is due to external radiation will be obtained from the EPR result by subtraction of the background dose and the component due to internal radiation, which is evaluated in the frame of WP3.4.

 Comparative analysis of external individual doses derived from EPR measurements and calculated according to the TRDS-2006 approach will be performed that allow validating and verifying calculated dose values and their uncertainties. Verified estimates of external doses will be used to improve Techa River dosimetry system and then to evaluate individual doses for the Techa River cohorts in the frame of work package 3.5.

WP3.2 Evaluation of the Techa River dosimetry system with luminescence measurements of building materials

Workpackage Leaders: Peter Jacob (GSF), Nikolai Bugrov (URCRM)

 Luminescence measurements with bricks and ceramic materials like electric isolators have been shown to enable absorbed dose determination in the measured materials since their production in the kiln. The absorbed dose due to anthropogenic sources can be obtained after subtraction of the contribution due to natural sources of ionizing radiation. Gamma-dose values in air can be derived by combining luminescence measurement and Monte Carlo simulation of the photon transport from the radioactive sources in the environment to the dose absorbed in air and in bricks. The Techa River dosimetry system (TRDS) uses the estimates of gamma-dose in air (as intermediate quantities for the determination of external exposures of people), which are based on historical monitoring data in combination with environmental modelling results. The comparison of values used in the TRDS with the results derived independently from luminescence measurements provides the basis for the validation of the external dose estimates and for the improvement of the Techa River dosimetry system.

The validation of external doses using luminescence measurements has been performed for Metlino which was the village (located 7 km downstream of the release point) with the highest external exposures. A confirmation of the value 27 Gy used in the TRDS for the cumulative gamma-dose in air on the riverbank has been presented in a series of publications. Validation of external doses at the remaining villages is still an open question which needs an active investigation.

 At the same time, the state of the art of dose reconstruction with luminescence measurements of samples from the middle Techa (Muslyumovo, a settlement 78 km downstream) has demonstrated that it is possible to reconstruct low-level anthropogenic doses within single bricks with the accuracy about 12%. The last finding shows that the validation task (analogous to that has been done for the upper Techa) can be performed for the middle Techa, a region where the significant number of the Techa River cohort members were exposed. This task is planned in the frame of WP3.2.

 The work will focus on Muslyumovo, a settlement located in the middle Techa region (78 km downstream of the release point). Muslyumovo is the unevacuated settlement that is closest to the release point. About 4,000 members of the ETRC and ETROC were exposed in this site. Thus, the validation of external dose can improve the quality of dosimetric data for these persons as well as for the residents of neighbour settlements located downstream the Techa River. Thus the validation with luminescence measurements will improve the TRDS-2000 for 20,000 members of the ETRC and ETROC, who live or lived in Muslyumovo and downstream of Muslyumovo.

 The evaluation of the Techa River dosimetry system with luminescence measurements of building materials needs the exploration of sites of dose reconstruction, the sampling, the determination of the anthropogenic dose in the samples, the simulation of the photon transport in the source-detector geometry at the site, the derivation of effective strengths of the different source areas of interest, and finally the determination of the absorbed dose in air at various locations at the sampling site. In previous projects (SURF and ISTC 509), the anthropogenic dose in a few samples from Muslyumovo mill (located at the bank of the Techa River) were reconstructed but a full-scale validation task was not performed for this site.

WP3.3 Internal dosimetry (fetal and infant) for the Techa River offspring cohort

Workpackage Leaders: Alan Phipps (HPA), Evgenia Tolstykh (URCRM) 

Members of the Extended Techa River Offspring Cohort (ETROC) can be at risk of radiation effects due to a number of factors, including: exposure of parental gonads before conception; exposure in utero; and exposure during the early years of life. The first of these factors was dealt with under work funded by the US Department of Energy (USDOE). This contract will be concerned with in utero exposures due to incorporated radionuclides, and with exposures during the early years of life due to intakes in breast milk and other foods.

 It is known that a significant part of ETROC cohort was exposed to ⁹⁰Sr in utero and during the first years of life. Precise dose evaluations for these people requires  improvements in Sr biokinetic and dosimetric models for foetus and infant. In recent years there have been a number of international developments in fetal dosimetry and in the modeling of radionuclide transfer to breast milk following intakes by the mother. It is essential to use this work as a basis for improvements to ETROC dose assessments.

 Reliable dose estimates are especially important for persons who were born in the period of maximum releases (1950-1952), since this part of the ETROC cohort will have a particularly important bearing on the risks derived in Subproject 4. The results obtained in this study that are needed for individual dose calculation for ETROC, will be mainly available at the end of month 24. Subsequently, work will continue on the scientific tasks of WP 3.3, which are aimed at further improvement of the approaches to ETROC dose estimation.

 WP3.4 Dosimetry for ⁹⁰Sr in teeth

 Workpackage Leaders: Yeter Göksu (GSF), Eleny Shishkina (URCRM)

The objective of this WP is the estimation of ⁹⁰Sr contribution to the total enamel dose for teeth of Techa River residents and Mayak PA workers. In order to achieve this objective the following work steps will be performed: the concentration of ⁹⁰Sr in the tooth tissues will be estimated with contact luminescence beta detection; the tooth geometry will be defined; the electron transport will be simulated; and the internal dose values will be evaluated. The state of the art is a qualitative evaluation of ⁹⁰Sr concentration in the calcified tissues using TL (thermoluminescence) thin layer dosimeters and conversion of results to internal enamel dose.

 Cumulative dose assessments based on EPR measurements of enamel result from two types of sources: external photons and internal incorporated radionuclides in enamel and dentin. Thus, whenever ⁹⁰Sr is incorporated into calcified dental tissue, the dose measured with EPR in enamel requires correction to give the true external dose. This workpackage will combine experimental measurement techniques with theoretical electron transport calculations (Monte Carlo) to provide estimates of enamel dose from ⁹⁰Sr/⁹⁰Y for Techa River residents and Mayak PA workers.

WP3.5. Reconstruction of radiation exposures relevant to the Techa River offspring cohort

 Workpackage Leaders: Marina Degteva (URCRM), Albrecht Wieser (GSF)

The progeny of the extended Techa River cohort (ETRC) members is identified as the extended Techa River offspring cohort (ETROC). Radiation factors that could exert influence on the TROC include exposure of parental gonads before conception; exposure of embryo/foetus during in utero period; and exposure of child in postnatal period. Thus, the doses both for parents (ETRC members) and children (ETROC members) will be considered in the framework of WP 3.5.

 TRDS-2006 being developed in the framework of Russian-US Project 1.1 will be used to determine individual doses for parents and children after birth. The TRDS is a modular database processor, that is, depending on the input data for an individual, various elements of several databases (or modules) are combined to provide the dosimetric variables requested by the user. These modules have been created in 2000 (the so-called TRDS-2000) and can be further updated or improved. It is planned to incorporate the achievements of the period after year 2000 in the framework of Russian-US project 1.1 as well as of Russian-EU projects (SURF, ISTC 509, SOUL) into a new version (TRDS-2006).

 Doses to pregnant women and the embryo/fetus are not considered in the TRDS. Special dosimetric coefficients and biokinetic models (that will be developed in the frames of WP 3.3) will be used to calculate fetal doses for ETROC members.

 The individual dose calculations for all members of ETRC and ETROC will be fixed in database Techa-Doses 2008 (to be completed by month 36).

 The work on dose calculations relevant to ETROC will start at the end of month 21 when the data for the corresponding modules of the TRDS-2006 become available. The results of parental and childhood dose calculations will be available at the end of month 30. Final results of fetal dose estimates will be available at the end of month 36. The analysis of revised dose distributions aimed at creating basis for a future ETROC dosimetry system will be continued up to the end of month 48.