Reliability of Using 238u/235u and 234u/238u Ratios From Alpha Spectrometry as Qualitative Indicators of Enriched Uranium Contamination

Abstract

Alpha spectrometry is a commonly used technique for the measurement of uranium isotopes in environmental samples because it is widely available at a relatively low cost. For natural uranium the (234)U to (238)U activity ratio should be 1 and the (238)U to (235)U activity ratio should be 21.7. However, a lower (238)U to (235)U ratio is usually observed in alpha spectrometric analysis of environmental soil samples. This observation has led to the conclusion that soils from nuclear weapons facilities were contaminated with highly enriched uranium. This study was undertaken to test the reliability of using activity ratios from alpha spectrometry to infer the presence of highly enriched uranium in soil samples. The results of these experiments indicate that the (238)U to (235)U activity ratio is not a reliable indicator, but that the (234)U to (238)U activity ratio can be used to qualitatively indicate the presence of highly enriched uranium at concentrations near 10 ng g(-1) and above.

Uranium-234, uranium-235 and uranium-238 in soil near Siberian Chemical Enterprises (Tomsk-7, Seversk)

“…The 234 U/ 238 U isotope ratio equal to 1,21. However Minteer et al [3] experimentally proved that alpha-spectrometric measurements of 234 U and 238 U ratio in the range from 1,03 to 1,29 may be due to the availability of the natural uranium only. Thus, the soils samples collected at 18 sampling stations in the sanitary zone of the SCE, zone of observation and on the territory of Seversk were analyzed.…”

“…Soil samples were processed in accordance with the standard procedure "Uranium-234, 235, 238. dissolving of samples in mixture of mineral acids, uranium concentration on Fe(OH) 3 , purification on anionic resin AV-17 and preparation of the thin alpha-spectrometric source. Air dried soil samples were powdered and sieved.…”

Application of neural network method to detect type of uranium contamination by estimation of activity ratio in environmental alpha spectra

“…The measurement of the activity of radionuclides and their ratios are very interesting for determining the composition of environmental and non-environmental materials in many applications including nuclear power industry, radioactive waste management and disposal, health physics, geology, geochronology, and environmental science (Fleischer, 2008;Minteer et al, 2007;Rubio Montero et al, 2004). Among analytical methods for isotopic determination of radionuclides, Alpha-particle spectrometry with silicon detectors is known as an appropriate, precise, and low cost technique to assay alpha-particle emitting elements such as Uranium isotopes (Jia et al, 2005;García-Toraño, 2006;Kunzendorf, 1968;Minteer et al, 2007).…”

“…Among analytical methods for isotopic determination of radionuclides, Alpha-particle spectrometry with silicon detectors is known as an appropriate, precise, and low cost technique to assay alpha-particle emitting elements such as Uranium isotopes (Jia et al, 2005;García-Toraño, 2006;Kunzendorf, 1968;Minteer et al, 2007). The activity ratios, for example in nuclear power industry, depend on the extent of the enrichment process, which have caused depletion in the lighter uranium isotopes and can be used for distinguishing natural from anthropogenic sources of uranium (Minteer et al, 2007). For natural uranium, the 234 U/ 238 U activity ratio in soil typically ranges from 0.5 to 1.2 (Sansone et al, 2001;Minteer et al, 2007).…”

“…The activity ratios, for example in nuclear power industry, depend on the extent of the enrichment process, which have caused depletion in the lighter uranium isotopes and can be used for distinguishing natural from anthropogenic sources of uranium (Minteer et al, 2007). For natural uranium, the 234 U/ 238 U activity ratio in soil typically ranges from 0.5 to 1.2 (Sansone et al, 2001;Minteer et al, 2007). The corresponding 235 U/ 238 U activity ratio is approximately 0.046.…”