354 



the helicopter waits with its engines running prevents investigating an adequately 

 representative area around the shaft in which the Srst nuclear explosion was conducted 

 (shaft No. 61), not to mention the increased levels of gamma radiation recorded by 

 airborne gamma-spectrometric survey in marshy river floodplanes, where only a few 

 measurements and random sampling could be made (sector No. 2 of the airborne 

 gamma-spectrometric survey, the Telgespit River valley). 



As a result, in the sector 'T»feva-3" one profile was made through shaft No. 61, 400 

 m long with azimuth 20* (fixed measurements at 20 m intervals, gamma radiation values 

 fi-om 8 to 12 /ir/hr and beta radiation values of 1 to 4 particles/min.cm^). During three 

 landings in the Telgespit River valley, 7-11 /ir/hr and 2-4 beta-particles/min.cm^ were 

 recorded within the boundaries of the gamma fields from the data of the airborne 

 gamma-spectrometric survey with an intensity of up to 20 /xr/hr (in each case, one 100- 

 120 meter long profile was passed). 



The 'Taas-Yuryakh" site, (town of Taas-Yuryakh, shaft No. 47). 



The shaft is located 7 km from the town Taas-Yuryakh up the Taas-Yuryakh 

 River on its right bank. According to the information provided by the Production 

 Geological Association Lenaneftegazgeologiya, an underground nuclear explosion was 

 conducted in shaft No. 47 in 1979. There is a sign at the shaft mouth saying "Shaft No. 

 47, started July 1981, completed February 1986." There is no clear reason for this 

 discrepancy. 



The sector was not investigated in detail, the trunk line (800 m) ran through 

 shafts No. 47 and No. 55 (located 100 m at azimuth 50*, started October 1981, completed 

 January 1986), three profiles at 100 meter intervals, 280 m long, and a route along the 

 river bank. The natural rock gamma background was 9-11 /ir/hr. 



A spot of radioactive contamination was found 100 m from shaft No. 47 at 

 azimuth 315* with an intensity of gamma radiation on the surface of 113 /ir/hr against 

 the background of 11 lit/hr and a beta radiation flux of 22 particles/cm^ -min against the 

 background of 2-4 particles/cm^ min. During detailed study of a 50 x 50 m square area 

 at a scale of 1:500, a maximum radioactivity of 230 /xr/hr was recorded (on the surface) 

 [illegible] tit/hr as well as the 33 particles/cm^ -min flux of beta radiation against the 

 background of 6 particles/cm^ -min (Figure 13). 



Gamma radiation was caused by cesium- 137, the spectrum of which was read out 

 by RSI-IOIM (Figure 11). 



Sofl sample No. 47/1 was taken from a point with maximum activity. On the 

 outline of the spot (98 Mr/hr), in a 0.5-m deep bore hole, two samples were taken from 

 the siuface of No. 47/2 and at a depth of 0-5 m in No. 47/3. The total beta activity of 

 the samples was 148.3, 32.4 and 16.4 x 10'^ Ci/g, respectively, which permits the 

 conclusion that the contamination did not go iar below the surface. 



