Alpha-Recoil Effects of Uranium Isotopes in Radioactive Minerals

Abstract

Alpha-recoil effect / Uranium isotopes I Radioactive minerals / Leaching/Radioactive disequilibriumAbstract A series of leaching experiments with H 2 0, HCl, HN0 3 and HF were carried out on pitchblende samples from Canada, Africa and China, a sample of uranotemnite from China and a sample of carnotite from Colorado, U. S. A. Marked enhancements of the 234 U/ 238 U ratio over the radioactive equilibrium value of 1.00 (Ci/Ci) were observed in some of the uranium fractions obtained from these radioactive minerals. (For example, a value of 23.8 ± 3.8 (Ci/Ci) was obtained for the J34 U/ 238 U ratio in a leaching fraction of carnotite.) However, the 23 5 U/ 238 U ratios were found to remain close to the normal value of 0.046 (Ci/Ci) within the experimental uncertainties.

Variation of the Isotopic Composition of Uranium in the Atmosphere

“…The 234 U/ 238 U ratios observed for the rain samples collected on 14 September, 27 September, 16 October, 18 November and 31 December 1984 were 0.50 ± 0.03, 0.60 ± 0.05, 0.52 ± 0.03, 0.57 ± 0.12 and 0.57 ± 0.11 (Ci/Ci), respectively. These values are similar to the value of 0.65 ± 0.02 (Ci/Ci) observed for a sample of Chinese uranotemnite [9], which is a grey-colored fluffy secondary uranium mineral. The 234 U/ 238 U ratios of six samples of uranium extracted from this mineral in the acid-leaching experiments ranged from the minimum value of 0.60 ± 0.03 and the maximum value of 1.88 ± 0.02 (Ci/Ci).…”

“…It is well known that a wide variation in the 234 U/ 238 U ratio occurs in nature due to the alpha-recoil effects of uranium atoms [8][9][10]. The 234 U/ 238 U ratios which we have observed for a few selected samples of natural waters, such as river, lake, well water and hot springs, and also some of the uranium minerals and their acid residues [8,9] are plotted in Fig. 2 for comparison.…”

Chemical Weathering (U-Series)

“…. Later work would explore how these processes could account for radioactive disequilibrium in geological materials with a focus on recoil and preferential leaching effects (Kigoshi 1971, Fleischer and Raabe 1978b, Fleischer and Raabe 1978a, Fleischer 1980, Fleischer 1982a, Fleischer 1982b, Fleischer 1983, Sheng and Kuroda 1984, Hussain and Lal 1986, Dran et al 1988, Adloff and Roessler 1991. Despite a large body of early work on U-series isotope fractionation during chemical weathering, the 1980's and 1990's saw a decrease in interest for this application.…”