Chernobyl fallout studied by Mössbauer spectroscopy V. Rusanov V. Gushterov Department of Atomic Physics, University of Sofia, Bulgaria H. Winkler A.X. Trautwein University of Lübeck, Germany Computer simulation of the radioactive contamination distribution over the northern hemisphere shortly after the accident. “Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal 2009”

Air photograph of the destroyed reactor block of the nuclear plant in Tschernobyl, Ukraine. About people were exposed to heavy irradiation. Among the rescue teams about 7000 people died. According to information from WHO people were severely falling sick. Because of danger due to radioactivity people had to be resettled. Even today inhabitants are suffering from the remainders of the accident. Children in Belarus experience the highest rate of cancer of the thyroid gland world wide. Altogether in Ukraine, Belarus and Russia an area as large as one third of the area of Germany is contaminated. Source and Photo: DPA V. Rusanov, V. Gushterov, H. Winkler and A. X. Trautwein, Chernobyl fallout studied by Mössbauer spectroscopy

Gross beta radioactivity of the atmospheric aerosols in Sofia Year Tests (courtesy of Mrs. B. Veleva) Jan Apr Jul Oct mBq/m mBq/m mBq/m mBq/m mBq/m 3 - background values Dec

V. Rusanov, V. Gushterov, H. Winkler and A. X. Trautwein, Chernobyl fallout studied by Mössbauer spectroscopy , Sofia , Sofia1994, Sofia Top left - mean value of the beta radioactivity of atmospheric air based on 5 different sampling regions in Bulgaria; top right and bottom left: autoradiography of air filters dated as shown, the bright spots are “hot particles” with very high specific radioactivity; bottom right - autoradiography of a tree leaf grown on 90 Sr contaminated soil near Sofia Mean value of gross beta radioactivity of the atmospheric aer, Bq/m 3 Days after the "zero" day of the Chernobyl accident

V. Rusanov, V. Gushterov, H. Winkler and A. X. Trautwein, Chernobyl fallout studied by Mössbauer spectroscopy Mössbauer spectra of an air filter collected during taken at 293 K and 77 K. This sampling time coincides with the maximum contaminating fallout due to the Chernobyl accident detected in Bulgaria. Measurements confirmed the presence of large quantities of magnetite Fe 3 O 4, mixtures of various oxyhydroxides mainly γ-FeOOH, a superparamagnetic component, and Fe 3+ in clay and silicate minerals. The Mössbauer spectrum taken at liquid nitrogen temperature shows that a considerable part of the ultra fine particles of α-Fe 2 O 3 (particle size less than 20 nm) had been in superparamagnetic state at room temperature. The iron concentration in air of 3.69 μg/m 3 was high and typical for days with large air pollutions.

V. Rusanov, V. Gushterov, H. Winkler and A. X. Trautwein, Chernobyl fallout studied by Mössbauer spectroscopy Mössbauer spectra of an air filter collected during taken at 293 K and 77 K. Change in the chemical composition including the presence of α-Fe 2 O 3 and oxyhydroxides, as well as absence of magnetite, were detected. The iron concentration remained high – 3.61 μg/m 3.

V. Rusanov, V. Gushterov, H. Winkler and A. X. Trautwein, Chernobyl fallout studied by Mössbauer spectroscopy Mössbauer spectra of an air filter collected during taken at 293 K and 77 K. In the Mössbauer spectra a magnetically split component was not detected at room temperature. Small quantities of α-FeOOH and γ- FeOOH were measured in the liquid nitrogen temperature spectrum. The measured iron concentration was extremely low, 0.79 μg/m 3, which is typical for days of small air pollution.

Fit results from the sum of three Mössbauer spectra of air filters collected between and The consecutive measurements showed clearly that after the first wave of radioactive contaminations from May 1 st to May 5 th the concentration of iron in the air dropped considerably. The overall pollution was not caused by a single radioactive wave. New contaminations and redistribution of the radioactive fallout had been detected. V. Rusanov, V. Gushterov, H. Winkler and A. X. Trautwein, Chernobyl fallout studied by Mössbauer spectroscopy

The results from the first air filter of Chernobyl fallout (black) were compared to results from air filters collected long after the accident on days of high (red) pollution (windy summer days) and low (blue) pollution (winter days after snowfall). The comparison confirms the major conclusion that the aerosols collected right after the Chernobyl accident contain magnetite, Fe 3 O 4. Magnetite is, as usual, nonstoichiometric and partially oxidized to maghemite, γ-Fe 2 O 3. Such contamination of the air over Sofia is not unusual. In days of high air pollution we detect magnetite, which most probably originates from the steel production plant near Sofia. Nevertheless, the magnetite concentration in the filter from right after the accident is 2-3 times higher and, therefore, is mainly a result of the polution due to the accident. V. Rusanov, V. Gushterov, H. Winkler and A. X. Trautwein, Chernobyl fallout studied by Mössbauer spectroscopy

Conclusion The increase of iron-containing material in the air pollution as a result of the Chernobyl reactor accident was expected. B. and M. Kopcewiczs were the first to use Mössbauer spectroscopy for such studies of air filters from Warsaw [1]. Our own results obtained with the filters from Sofia [2] confirm that for the initial filters, collected during the contaminating fallout ( ), the iron concentration was highest and magnetite Fe 3 O 4 was present. This is most likely due to the fact that during the accident large amounts of iron-construction materials were destroyed, evaporated and transported together with the radioactive fallout. The presence of magnetite particles of industrial origin in air pollutions in Sofia is not exceptional and originates mostly from the steel plant situated nearby. Nevertheless, the major Chernobyl fallout in Bulgaria happened during four consecutive holidays after May 1 st, and we could assume that on these days the industrial plants had worked on minimal power. During these days the magnetite concentration in the air filter was 2-3 times higher compared to that from days with high air pollution in Sofia. This finding confirms that the large part of the iron-containing contaminations was caused by release from the reactor accident. A definite conclusion about an increase of the isotope abundance of 57 Fe in the Chernobyl fallout cannot be based on Mössbauer spectroscopy only. Additional mass-spectroscopic measurements are needed. [1] B. Kopcewicz and M. Kopcewicz, Hyperfine Interactions, Mössbauer study of iron-containing atmospheric aerosol collected during the Chernobyl accident, 139/140, (2002). [2] V. Rusanov, V. Gushterov, H. Winkler and A. X. Trautwein, Iron-containing atmospheric aerosols in the Chernobyl fallout, Hyperfine Interactions, 166, (2005). V. Rusanov, V. Gushterov, H. Winkler and A. X. Trautwein, Chernobyl fallout studied by Mössbauer spectroscopy Acknowledgements The authors are indebted to Mr. V. Mavrodiev for providing the filters. Thanks are due to the Alexander von Humboldt Foundation, special program Stability Pact for South Eastern Europe (V. R. and A. X. T.).