356 



displayed a relatively high radioactivity of 10-15 /xr/hr. Around the site of explosions the 

 natural gamma background of rocks does not exceed 14 /xr/hr. 



We present these data as a basis for further investigation of the radiation situation 

 at sites of underground nuclear explosions, so as to identify radioactive contamination 

 spots against this background. 



The Udachny site. It was not included in the plan of operations due to lack of 

 information available to the Coordinating Council on the nuclear explosion conducted 

 there. According to the information obtained from the executive committee of the city 

 council and the sanitation and epidemiology station of the city of Udachny, an 

 underground (near-surface) nuclear explosion was conducted 2.5 km northeast of the 

 town of Udachny in 1S>74 for the construction of a water reservoir dam. A powerful 

 outburst was observed by witnesses. 



The radioactivity at the site of the explosion was 50-65 /ir/hr on the surface, and 

 up to 200 /ir/hr at a depth of 0.4 m in the excavation. 



The results of our investigation are set forth in a document attached to this report 

 (see Appendix No. 5). 



According to data from the airborne gamma-spectrometric survey conducted last 

 August, radioactive contamination was recorded both above the explosion crater and in 

 the cloud traces (Figure 11). 



In the future, the area of airborne gamma-spectrometric survey must be extended 

 for monitoring the cloud traces, and detailed surface operations must be conducted at 

 the site of the explosion and contamination spots. The fact that radioactive 

 contamination was recorded in the uranium chaimel during the airborne gamma- 

 spectrometric survey (Figure 12) also requires explanation. 



The Aykhal site (Kraton-3). 



The natural gamma background of the territory was studied during large-scale 

 prospecting for uranium by the geologists of the Amakinsk expedition in 1971-1973 

 (M.V. Gavrilyuk et al. Report on the Work of the Khalamanit Team for 1971-1973. 

 Materials for the state geological map, 1:50,000 scale, sheets 0-49-81-B, T and 0-49-82- 

 A^3- Nyurba, 1973). The radiometric survey on a scale of 1:50,000 was made over an 

 area of 1,061.7 km^ with SIT-2 radiometers; gamma profiling of a bore hole 1,323 linear 

 meters deep and 801.8 m-^ of trenches was performed. 



Procedure: Large-scale uranium prospecting was conducted simultaneously with 

 geological mapping. It involved continuous listening through a telephone with 

 measurements made after each 50 m and regardless of the interval when the rock 



