Determination of uranium and thorium isotopes in soil samples by coprecipitation

The paper presents a procedure to prepare soil samples for U and Th isotope measurement by alpha-spectrometry after coprecipitation with LaF3. In this procedure the reduction of U(VI) to U(IV) was performed by Zn metal in 4M HCl solution. The recoveries of chemical separation equal to e(U-chemistry) = 78 +/- 4% for uranium and e(Th-chemistry) = 82 +/- 4% for thorium. Canberra alpha-spectrometer was used with PIPS detectors of A-1200-37-AM Model of 1200 mm(2) active area. The counting efficiency of the measuring system equals to e(counting) = 18% and the total efficiencies were e(U) = e(counting) (.) e(U-chemistry) = 14.0 +/- 0.7% for uranium and e(Th) = e(counting) (.) e(Th-chemistry) = 14.7 +/- 0.7% for thorium. The recoveries of chemical separation were rather high (about 80%), that leads to the use of a small weight of soil sample (about 0.5 g). The efficiencies were also stable, that allows analyzing the soil sample without using radiotracers. They are advantages of the sample preparation procedure of this work.