Measuring the External Exposure Dose in the Contaminated Area Near the Chernobyl Nuclear Power Station Using the Thermoluminescence of Quartz in Bricks

Abstract

We collected bricks from buildings in the heavily contaminated evacuated area of Belarus in a 30-km zone around the Chernobyl nuclear power station and the Gomel-Bryansk area of 150-250 km from Chernobyl and estimated the cumulative radiation dose caused by the reactor accident by measuring the thermoluminescence (TL) of the bricks. The annual dose at each location was measured using glass dosimeters and thermoluminescence dosimeters (TLD). The dose rate was measured using an energy-compensated NaI scintillation survey meter. The soil contamination near the location of each brick was measured using a germanium semiconductor detector. The main purpose of the project was to extrapolate the relation between the cumulative external dose and the present dose rate or contamination level to the lower contaminated areas. The results of the glass dosimeter, TLD, and survey meter determinations were almost identical. For a determination of the annual dose higher than 10 mGy y(-1), the cumulative dose by TL (TL dose) was roughly proportional to the annual dose and about 1.5 times larger than the cumulative dose calculated from the annual dose and 137Cs half life. The difference is expected due to the contribution of short-lived nuclides immediately after the accident or localized heavy contamination of the ground surface with 137Cs that migrated afterwards. For annual dose smaller than 10 mGy y(-1), the proportionality was not observed and most of the locations facing indoors showed TL doses very much larger than that expected from the proportionality. The cumulative dose outdoors by TL was also roughly proportional to the regional 137Cs contamination level and the proportional constant is about 10(-1) mGy per GBq km(-2), and is about 250 times larger than the present annual internal dose derived from published results. The correlation between the present dose rate where the brick was sampled and the average 137Cs concentration in the ground soil near the point is not clear, possibly because of the large spatial fluctuation in the 137Cs concentration in the soil.

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

“…Although some exploratory retrospective work commenced within areas heavily contaminated by fallout from the Chernobyl reactor within five years after the accident (Bailiff, 1997), the work to obtain closer integration of luminescence techniques with the established approaches of dose reconstruction only commenced several years later. In an initiative that formed part of the Chernobyl Sasakawa Health and Medical Foundation Project (Hoshi et al, 1994) a joint JapaneseBelarusian team undertook fieldwork to sample buildings in 14 contaminated settlements Belarus (Sato et al, 2002). Working independently from the effort underway in Belarus, a collaborative group of institutes from the EU states, the Ukraine and Russia undertook fieldwork in three settlements in the Ukraine and Russia (Bailiff et al, 2004a andBailiff et al, 2005).…”

“…The study undertaken during 1994 in Belarus by the Japanese-Belarusian team (Sato et al, 2002) examined one building in each of 5 settlements within the 30 km Exclusion Zone and 9 settlements located in a NNE direction between ca 150 and 250 km from the NPP in the Mogilev oblast (Supplementary Material, Fig. SM1), and it appears to be the only published report of a multi-settlement study of settlements in Belarus.…”

“…Although a detailed approach was taken in the fieldwork procedures, the cumulative dose determinations obtained with brick, DX, (denoted Dn in Sato et al, 2002), particularly from interior locations of sampled buildings, presented inconsistencies and difficulties in interpretation that limited the extent to which they could be applied more generally to settlements with lower levels of contamination (i.e., <1000 kBq m −2 ). The main difficulty encountered in the Belarus study was finding that the cumulative dose to brick located within the interior of most of the buildings was significantly higher than expected for contamination deposited externally on the ground.…”

“…Notwithstanding these problems at a detailed level, Sato et al (2002) extract a form of dose conversion factor from a plot of the values of DX for external brick vs the official settlement areal 137 Cs activity (Fig. 12 in Sato et al, 2002).…”

“…12 in Sato et al, 2002). For the period extending from the onset of delivery of fallout to the middle of 1994, when the samples were extracted, a value of ∼0.1 mGy per kBq kg −1 for the cumulative gamma dose was derived, noting that the calculation is based on a dose value at the exposed brick surface.…”