Application of the Mössbauer effect in investigations of iron concentration variations with air radioactivity

The Mössbauer effect was applied in the study of concentration of iron in the atmospheric air in relation to the air radioactivity. A correlation between air radioactivity due to nuclear explosions and concentration of iron was observed. The experiments were performed by observing the resonance absorption of 14.4 keV gamma rays from 57Co by samples consisting of filters through which atmospheric air was pumped. The Mössbauer effect measurements were performed at room temperature. The concentration of iron-57 calculated using the “area method” varied from 0.54 times 10^-2 µg/m³ to 12.22 times 10^-2 µg/m³ in correlation with air activity variation from 0.05 pCi/m³ to 9.16 pCi/m³, depending on site and period of time. From the shapes of the Mössbauer spectra obtained it was inferred that iron appears in the Fe₂O₃ compound. The fresh fallout (high activity) contains a mixture of two dominating sizes of particles: small ones ( 100 à) in the form of ultrafine particles in the superparamagnetic state, and large ones, which contribute to the magnetic part of the spectra. The old fallout (low activity) contains small particles only. It testifies that large particles containing Fe₂O₃ originate mainly from the nuclear explosions.