Issues in the Reconstruction of Environmental Doses on the Basis of Thermoluminescence Measurements in the Techa Riverside

Abstract

The potential of thermoluminescence measurements of bricks from the contaminated area of the Techa river valley, Southern Urals, Russia, for reconstructing external exposures of affected population groups has been studied. Thermoluminescence dating of background samples was used to evaluate the age of old buildings available on the river banks. The anthropogenic gamma dose accrued in exposed samples is determined by subtracting the natural radiation background dose for the corresponding age from the accumulated dose measured by thermoluminescence. For a site in the upper Techa river region, where the levels of external exposures were extremely high, the depth-dose distribution in bricks and the dependence of accidental dose on the height of the sampling position were determined. For the same site, Monte Carlo simulations of radiation transport were performed for different source configurations corresponding to the situation before and after the construction of a reservoir on the river and evacuation of the population in 1956. A comparison of the results provides an understanding of the features of the measured depth-dose distributions and height dependencies in terms of the source configurations and shows that bricks from the higher sampling positions are likely to have accrued a larger fraction of anthropogenic dose from the time before the construction of the reservoir. The applicability of the thermoluminescent dosimetry method to environmental dose reconstruction in the middle Techa region, where the external exposure was relatively low, was also investigated.

Retrospective and emergency dosimetry in response to radiological incidents and nuclear mass-casualty events: A review

“…Initial work by Bougrov et al (1995) had shown that the levels of cumulative dose registered in bricks from the Old Mill, ranged from 1 Gy (walls facing land) to 5 Gy (walls facing the reservoir), and that the cumulative background dose was ∼0.5 Gy arising from the substantial age of the buildings. The latter was checked by dating brick from a heavily shielded location in the mill and the resulting luminescence age of 129 ± 14 years was consistent with available documentary evidence (Bougrov et al, 1998). Although the NNW facing walls of the Old Mill and the Granary are of particular interest because part of the settlement was distributed around the shores of Metlinsky Pond, more recent work has focused on the SW wall of the Old Mill (Fig.…”

“…When examining the values of DX , Tarenenko et al, 2003and Bougrov et al, 1998 obtained for the SW wall of the Old Mill for the same depth range (10 ± 5 mm) and the same height, an overdispersion (ca 15-20%) was observed, unexpected given the relative proximity (several m) of the sampled locations. Jacob et al (2003) concluded that, although not significantly affecting the median value of DX calculated for each height, some of the overdispersion could be attributed to systematic errors arising from one of the techniques applied.…”

“…Although this may not be a significant factor for measurements on the timescale of interest in retrospective dosimetry, additional experimental checks are required to establish the rate of loss of trapped charge (Huntley and Lamothe, 2001). Also, when using this size fraction there is a substantial increase in DBG caused by the registration of alpha dose in grains that are of size less than the average range of the alpha particles emitted by lithogenic radionuclides present in the ceramic, and this may affect the precision with which DX can be determined when it falls within a low dose range (i.e., <100 mGy) (Bougrov et al, 1998).…”

“…Of primary interest is whether the reliability of dose estimates for the period 1949-1956 can be improved by judicious choice of sample locations, the selection of which is expected to be sensitive to changes in source geometry. Fortunately, although published relatively late in the sequence of experimental work (Bougrov et al, 1995, Bougrov et al, 1998, Göksu et al, 2002aand Tarenenko et al, 2003, more detailed information regarding the hydrological history and management of the fluvial system became available (in Russian) in 2005, and Degteva et al (2008) clarify how the changes to water management affect the interpretation of results from the earlier work (see caption to Fig. 46).…”

“…Estimation of the cumulative dose at a reference location for the period of interest (1949)(1950)(1951)(1952)(1953)(1954)(1955)(1956)) requires the separation of the contributions to the cumulative dose made before (1949)(1950)(1951)(1952)(1953)(1954)(1955)(1956) and after the creation of Reservoir 10 during the autumn of 1956. Advancing the earlier work of Bougrov et al, 1998 andTarenenko et al, 2003 constructed a 2-stage model for radiation transport simulations based on 'river' and 'reservoir' configurations of sources, corresponding to the pre-and post-evacuation stages. A calculated estimate of 0.35 Gy (2σ range, 0.2-0.6 Gy) was obtained for the cumulative dose during the post-evacuation period (1957-1997) using contemporary and historic monitoring and sediment radioactivity data for the reservoir floor and river channel deposits.…”