Radiation exposure of human populations in villages in Russia and Belarus affected by fallout from the Chernobyl reactor

Detta är en avhandling från Medical Radiation Physics

Sammanfattning: A quarter of a century has elapsed since the catastrophe at the nuclear power plant in Chernobyl. The radioactive fallout affected all the European countries and most severely the three countries of Belarus, Russia and Ukraine. In the aftermath of this devastating event, the scientific knowledge on the various radiological impacts of such a large scale accident and means to remediate these impacts has increased and will be essential for the future. The inhabitants that live in the most contaminated areas are, however, still exposed to elevated levels from the residuals of the Chernobyl fallout. This means that continued assessment of the long-term impact still is required to meet the concern of the affected people. In this thesis, the current day exposure to inhabitants living in some of the villages in the Bryansk region (Russia) have been assessed using similar methods of individual monitoring as during earlier phases of the project (1991-2000). This included personal TLDs and individual whole body burden estimates of 137Cs by NaI(Tl) measurements. A method applicable for prospective as well as retrospective absorbed dose estimates has also been evaluated by using the optically stimulated luminescence in ordinary household salt. The dosimetric potential of salt was investigated in the laboratory with the aim to use salt as a retrospective dosemeter. The salt dosemeters were also tested for prospective in situ measurements together with TLDs and model estimates based on point measurements by means of a high pressure ionisation chamber and ordinary radiation protection instruments. These measurements were carried out at various (stationary) positions in a contaminated village in Belarus, not far from the villages in the Bryansk region. Today the radiological importance is completely dominated by 137Cs. The contamination level of 137Cs varies significantly between different villages, within the villages and even within the gardens of individual residences. The external exposure is thus dependent on where an individual resides. The internal exposure is associated with the intake of forest food (mushroom, berries and game), rather than the contamination level within a specific village. As an average, the inhabitants in the Russian villages received a total annual effective dose due to Chernobyl caesium of 0.5 mSv y-1 and 0.4 mSv y-1 in 2006 and 2008, respectively. This corresponds to a reduction of more than 60% over 10 years. In 2006 and 2008 the internal component was 1/3 of the total effective dose and the remaining external component was around 0.35 mSv. As the rate of decrease of the external exposure is relatively stable the internal effective dose, which has a different temporal behaviour, is predicted to become of increasing importance in the future. The comparative measurements in the Belarusian village showed a good agreement, and predicted an external effective dose of about 1 mSv y-1. The overall results show that the effective dose to the inhabitants in the investigated area is now close to a level that is comparable to the natural background radiation. The study also shows that the potential of ordinary household salt as a tool for dosimetry is promising, also for prospective measurements in situ and at low absorbed doses and dose rates.

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