SUMMARY
Uranium is a radioactive element with a special presence in the rocks, waters, sediments, soils, and plants at the state of Chihuahua. The activity ratio of 238U/234U is used to explain the uranium transport by surface water and its deposition in arid environments. In this work, the activity concentration of natural U isotopes is determined by PERALS liquid scintillation and high-resolution alpha spectrometry (AS, Canberra camera 7401VR) in the Environmental Radiological Surveillance Laboratory (LVRA) at CIMAV, Chihuahua. Uranium is extracted from soils through the scintillating liquid extractor URAEX for PERALS, with chemical recovery (CR) of 80 - 85 %, and through the ion exchange resin UTEVA + electrode position by the Hallstadius method, with CR of 85 - 90 %, for AS. The procedures of 234U and 238U activity concentration (AC) determination in soils were validated by their application to the certified reference material IAEA-375. The resulting values were in the reference range of the certified or informative values. Both procedures were applied to 6 representative soil samples, with AC of the same order of magnitude or greater, and similar CR and compatible results. Both procedures are satisfactory for the purposes of LVRA research and in general.