Abstract
Alpha spectrometry using pulse height analysis has been used for the determination of uranium concentrations in different environmental samples. The concentration of 238U was measured by both destructive and non-destructive techniques with a detection limit of less than 1.8 mBq/kg. However, because of the extremely low 234U concentrations in environmental samples, it was necessary to use a destructive technique to separate U from the sample matrices as well as remove interfering elements from the sample solution to determine 238U/234U ratio. In this study, the uranium was separated from the environmental samples using anion exchangers in (Dowex 1 × 8 Cl? form) and purified via co-precipitation with Lanthanum fluorides (LaF3) and the alpha source prepared by electrodeposition. The results obtained were validated using some certified reference samples.
Highlights
Uranium is a widely distributed lithophile metallic element
The natural uranium consists of three radioisotopes; 238U, 235U and 234U with atomic abundances of approximately 99.275%, 0.72%, and 0.0055% respectively
The non-destructive techniques are mostly achieved by γ-spectrometry (e.g. NaI- and HPGe-detectors)
Summary
Uranium is a widely distributed lithophile metallic element. It may be present as a significant constituent in some minerals (e.g. uraninite, brannerite and carnotite) or as an accessory element in others (e.g. zircon, apatite, allanite and monazite). Its detection limit is typically 100 to 1000 times lower than γ-spectrometry [4] This technique is mostly used for detection and analysis of U as well as Th radioisotopes, in the environmental samples, such as natural waters, which are characterized with low radioactivity concentration levels [3,5]. Sample preparation aims to convert the sample into a thin layered, chemically isolated form that can be placed into the spectrometer and counted with a minimum alpha particle energy interferences and self absorption, and alpha peak broadening due to energy straggling with thick sources It is often an extensive process and requires several steps including: 1) sample digestion (preliminary treatment); 2) uranium separation and purification 3) alpha source preparation, and 4) alpha counting over extended periods for low detection limits. Several methods and flow charts have been reported in different literatures for sample preparation for U-analysis using α-spectrometry [6,10,11]
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