376 



Bq/kg. The contamination is of a surface nature, and radioactivity decreases with depth; 

 its origin is not clear, but may be "technological." 



"Kristall": 0.4x0.9 km, the exposure dose up to 65 /xr/hr, the maximum 

 radioactivity on the surface, 120 fXT/hr; the total b»eta activity in soil, 1860 (950) Bq/kg; 

 strontium-90, 483 (130) Bq/kg; in vegetation (reindeer moss) the total beta activity is 

 26,290 (10,760) Bq/kg; strontium-90, 788 (220) Bq/kg; cesium-137, 386 (166) Bq/kg. 

 Radioactive contamination was caused by a near-surface underground nuclear explosion. 

 The nature of the explosive operations (stripping) makes it possible to indicate a 

 predesigned discharge of radioactivity. 



"Kraton-3": spots of radioactive contamination were revealed by airborne gamma- 

 spectrometric survey throughout the entire area investigated (7x12 km); the main trace 

 was followed for 5 km, J to 2J km wide; the exposure dose in the axial portion of the 

 trace is up to 2(*0 Mf/hi> the maximum values .lear the shaft mouth on the siuface are 

 730 Mr/hr, the total beta activity in soil is 28,340 (670) Bq/kg; strontium-90, 9990 (47) 

 Bq/kg; cesiimi-137, 5120 (87) Bq/kg; in vegetation (reindeer moss) the total beta activity 

 is 3,378,000 (19,760) Bq/kg; strontium-90, 55,460 (197) Bq/kg; cesium-137, 19,150 (310) 

 Bq^cg. Radioactive contamination of the area was caused by an accidental discharge 

 during an imderground nuclear explosion; the scale of the event is not clear, the location 

 of contamination spots and parameters of the main trace of the radioactive cloud 

 indicate that the close trace extends for tens of kilometers. 



During the operations, 148 samples were taken, including 70 of soil, 14 of 

 vegetation, 43 of water, and 21 of food. In all 253 anafyses were performed, including 

 104 for the total beta activity, 23 for the total alpha activity. 111 radiochemical anafyses, 

 12 gamma-spectral analyses, and 3 analyses using a procedure with ion-exchange resins. 



Analysis of the total alpha activity of 20 samples firom the site "Kraton-3" and 3 

 samples from the site "Sheksna" produced results within average values of alpha activity 

 of the arable sofl of Yakutia, i.e. no alpha-emitting radionuclides at the sites of 

 radioactive contaminations examined. 



Special attention was given to testing water, 43 samples were taken, including 34 

 for the total beta activity, 6 for radiochemical analysis, and 3 samples using the 

 procedure of concentration of strontium-90 on ion-exchange resins. 



"Sheksna": 16 analyses of the total beta activity were carried out, one involving 

 application of ion-exchange resins for strontium-90, and radiochemical analysis of two 

 samples for strontium-90, cesium-137, uranium-238, and radium-226. In two samples, 

 taken on June 25, 1990 from the Ulakhan-Botuobuy and Taas-Yuryakh rivers, the total 

 radioactivity of 3.3X10**" and 2.3X10'"' c/1 was found, in others it was less than 

 IXlO'^'Ci/L A sample for strontium-90 with the use of ion-exchange resins taken 

 simultaneously from the Ulakhan-Botuobuy River showed 13.2 Bq/m^ (3.2 Bq/m^) in the 



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