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2. RESULTS OF WORK 



The form of the presentation of this section was motivated by the authors' 

 intention to preserve the authenticity of the following materials and methods. 



The procedure and the results of the airborne gamma-spectrometric survey that 

 are needed for understanding the text are given here in a very condensed form, because 

 they are set forth in detail in the airborne geophysical team's reports. 



2.1. Airborne Geophysical Work 



In Jime and August of 1990, the airborne geophysical team of the Central 

 prospecting survey expedition of the Production Geological Association Yakutskgeologiya 

 conducted an airborne gamma-spectrometric survey on the sites 'Taas-Yuryakh", "Aykhal" 

 and "Udachny". The suivey was performed with an airborne geophysical station SKAT- 

 77 mounted on an AN-2 aircraft The courses, plotted in accordance with a survey scale 

 of 1:25,000 over 250 m and 1:10,000 over 100 m, were tied in by aerial photographic 

 referencing using an AFA-17 aerial camera. Flight altitude was maintained within the 

 range of 50-75 meters above the surface. From the results of these aerial operations 

 gamma field maps were made of the "Taas-Yuryakh" and "Aykhal" sites with a scale of 

 1:25,000 and of the TJdachny" site on a scale of 1:10,000, which characterize the general 

 radiation background above said sites and the distribution of radioactivity over them. 



The "Taas-Yuryakh" site. The survey was performed on three separate sectors 

 No. 1, 2, and 3 (Figure 2). 



On the map of the gamma field of sector No. 1, the isolines are drawn every 2 

 /xr/hr. The maximum activity of the gamma field, which does jiot exceed 18 /ir/hr, is 

 observed only at the southernmost boundary of the sector, and the main portion of the 

 sector, including the town Taas-Yuryakh itself, is characterized by gamma activity levels 

 no greater than 12 /ir/hr. To understand the nature of the high (up to 18 ftr/hi) gamma 

 activity, detailed surface operations are required involving soil, vegetation and water 

 sampling. The nature of the gamma field in the area of well No. 47, the site of an 

 imderground nuclear explosion, is shown in Figure 3. A radioactive contamination spot 

 revealed by sur&ce operations was not recorded by airborne gammaspectrometiy, which 

 can be explained by low radioactivity. 



On the map of the gamma field of sector No. 2, the isolines are drawn every 5 

 Mr/hr. In general, sector No. 2 is characterized by the background value of the gamma 

 field, and only in certain areas of the Telgespit River valley and in the central part of the 

 area are values up to 20 nr/ta reached. In order to understand the nature of these 

 "spots", a complex of surface operations has to be conducted. In this sector four 

 underground nuclear explosions were conducted. The nature of the ganmia field above 

 the wells is norma] (Figures 4, 5). 



