Radioactive airborne particles from Chernobyl forest fires

The spring and summer, 1992 within 30-km zone near Chernobyl NPP were very hot and dry. That lead to forest fires in May (4 ... 9,23 ... 25), July (28 ... 30) and August (10...12). The Cs-137 soil contamination density (SCD) was equal to 1...400 Ci/km2 at various forest sections of combustion. The stationary air samplers with capacity of 1500 m3/h were used for the monitoring of aerosol emissions during fires. These samplers were situated at a distance of 5...10km from fires boundaries. Smoke particles were collected by the fibrous filters FPP-15-1,5 (Russia). After exposure the activity of aerosols of Cs which deposited by a filter was measured by a gamma-spectrometer. For the separation of Sr-90 and isotopes of Pu the radiochemical analysis was used. It was found that the concentration of Cs-137 increased up to 10...100 times compare with open-quotes backgroundclose quotes one even at several km from fires. The concentration of Cs-137 inside of combustion zone was estimated could exceed the Russian maximum permissible one both for population (0.49 nCi/m3) and for professionals (14 nCi/m3) if the SCD will be more than 0.5 and 7 Ci/km2, respectively. It was measured that Cs-137/Sr-90 and Cs-137/Pu-238 ratios increase in fire emissions. It is obviously, that such enrichment was a consequense of radioactive cesium evaporation at temperature more than 500 C. The experimental forest fire was carry out in August, 1993 in Bryansk region (Russia). The forest section with area 50x50 m was selected. The SCD of Cs-137 was equal to 30 Ci/km2. The Cs-137 concentration during the day before the experiment was equal to 0.16pCi/m3. The concentration was varied from 1.6 to 15 pCi/m3 during the experiment. For the determination of particle sizes the filter pack technique (Budyka et al, 1993) was used. It was found that particle size distribution was a bimodal in plume