Research and systematization of 'hot' particles in the Semipalatinsk nuclear test site soils - methodology and first results

Full text: Sources of soil activity in Semipalatinsk Nuclear Test Site (SNTS) could be both 'hot' particles dimensions from tens microns to units millimeters and sub-microns particles determining a matrix activity of soil samples. The fractionating of radionuclides and formation of 'hot' particles radionuclide composition arose from temperature changes and complicated nuclear-physical and thermodynamics processes occurring in a fire ball and cloud of nuclear explosion. Knowledge of 'hot' particles physical-chemical properties is needed for evaluation of radioactive products migration in the environment and danger level of the people external and internal exposure. Moreover, minute information about the structure and compound of 'radioactive' particles can be useful for specification of processes occurring in a fiery sphere when conducting explosions of different phylum and also for specification of radioactive fallout forming mechanism. The main polluted spots of SNTS could be divided into the four the species depending on nuclear explosion phylum. Species of radionuclide and their distribution for the different nuclear explosions are able to differ considerably. Therefore, several most typical areas for the each phylum test were selected and twenty soil samples were collected to reveal their radionuclide pollution peculiarities. Collected soil samples were separated into the five granulometric fractions: 1 mm - 2 mm, 0.5 mm - 1 mm. 0.28 mm-0.5 mm, 0.112 mm - 0.28 mm and <0.112 mm. Main objectives of the carried put works were confirmation of hypothesis of the 'hot' particles presence in SNTS soil samples and determination of soil samples fractions and single 'hot' particles activities. For this goal compelled fission and visual identification methods of the 'hot' particles separation and selection were development. Isotope compositions of the selected 'hot' particles were determined by the γ-spectrometric method. Carried out works have preliminarily shown that for researched soil samples bulk soil fraction activity is concentrated in 'hot' particles. At present 59 'hot' particles of first fraction (f>1 mm), 210 'hot' particles of second fraction (1>f>0.5 mm) and 154 'hot' particles of third fraction (0.5>f>0.28 mm) have been selection from the twelve SNTS soil samples by the compelled fission and visual identification methods. Main sources of soil samples and 'hot' particles activities are 239+240Pu, 241Am, 137Cs and 152Eu isotopes.In addition to the described works the special sampling of large 'hot' particles (dimension more than 2 mm) was carried out in areas of the ground and air tests. The 'hot' particles search was also based on the difference of 'hot' and soil particles shapes. There are two species of large 'hot' particles: 1. 'hot' particles with regular contours and flowed shapes looked like on the earlier selected 'hot' particles from the first and second fractions of soil samples. 2. 'hot' particles with irregular shape. Preliminary results of the researches are presented in this paper