Ranges of α-recoil 234Th atoms in uranium oxides

Abstract In order to interpret the anomalous activity ratios of 234 U/ 238 U observed widespreadly in natural waters, much attention has been paid on the direct α-recoil effect during the 238 U → α234 Th decay process. In the present work, the direct recoil of 234 Th from the surface of some uranium sources was studied as a function of the source thickness as well as their chemical composition. The sources used were shown to be amorphous UO 2 or crystalline U 3 O 8 by X-ray diffractometry. The α-recoil atoms, 234 Th and 231 Th, which originate in the decay of the parent nuclides, 238 U and 235 U, on the electrodeposited sources, were effectively collected on an aluminum plate collector placed opposite each source in a low pressure of about 10 −2 tort. The 234 Th-activity transferred to the collector was found to reach a limiting value for uranium-oxide thicknesses greater than 50 μg/cm 2 . Using these results, the recoil 234 Th ranges were determined to be 13.2 and 16.9 μg/cm 2 in the UO 2 and U 3 O 8 deposits, respectively. These ranges are compared with the ones calculated from the LSS-equation.