[en] The precision and accuracy attainable in direct complexometric titrations of Thsup(4+) consecutively with either lighter (La³⁺, Nd³⁺, Sm³⁺, Eu³⁺ or Gd³⁺) or heavier lanthanides (Dy³⁺) in different proportions using Semimethylthymol Blue (SMTB) as a metallochromic indicator and disodium dihydrogen ethylenediaminetetraacetate were studied. Thorium (IV) was titrated at pH 2, the Ph was adjusted to 5.5-6.0 by adding hexamethylenetetramine (hexamine) buffer and acetylacetone-acetone solution and La³⁺ (or Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺ or Dy³⁺) was then titrated. A comparison of the indicators SMTB and Methylthymol Blue (MTB) for successive titrations of Th⁴⁺ and any of the rare earth ions was carried out. The proposed titration method was applied successfully to some naturally occurring ores and minerals containing thorium and some lanthanides and the results were satisfactory. (Author)

[en] A new calixarene hydroxamic acid, 25,26,27,28-tetra-hydroxy 5,11,17,23-tetrakis(N-p-chlorophenyl)calix [4]-arene hydroxamic acid (CPCHA) is used for the extraction and spectrophotometric determination of thorium(IV). The molar absorptivity of the thorium(IV)-CPCHA-SCN complex is 2.2 x 10⁴ m² mol^-1 at 450 nm. The system obeys Beer's law over the range 1.3-13.2 ppm of thorium. The thorium-calixarene hydroxamate ethyl acetate extract was directly subjected to ICP-AES measurements which increases the sensitivity by fifteen-fold. Thorium can be estimated at the 0.1 ppm level. The method is applied for the trace determination of thorium(IV) in geological samples at the low ppb level even after a 1: 100 dilution (dissolution). (author)

[en] The optimization of alpha/beta separation in liquid scintillation using pulse shape analysis is convenient for the simultaneous determination of alpha and beta emitters in natural water and other samples. In this work, alpha/beta separation was studied for different scintillant/vial combinations and it was observed that both the optimum pulse shape discrimination level and the total interference value (that is, the summed relative interference between alpha and beta spectra) were dependent on the sample quenching and independent of the scintillant/vial combination. These results provide a simple method for modifying the counting configuration, such as a change in the cocktail, vial or sample characteristics, without the need to perform exhaustive parameter optimizations. Also, it was observed that, for our counting conditions, the combination of Ultima Gold AB scintillation cocktail with Zinsser low diffusion vials presented the lowest total interference, namely 0.94 ± 0.28%, which is insignificant for the counting of environmental samples. (Author)

[en] The underestimation (or reduction factor) of gold (¹⁹⁸Au) in ore samples due to the self-shielding of epithermal neutrons during epithermal neutron activation analysis (ENAA) was measured. Three synthetic ores with different size ranges of gold particles were prepared and analysed by NAA and ENAA. Epithermal neutron activation analysis was found to underestimate gold in synthetic ores containing gold particles with size ranges of ≤53, 53-150 and 150-250 μm by the factors 11, 31 and 33%, respectively, in comparison with NAA. A reduction factor of 5% was also measured for gold in reference ore MA-1, certified by CANMET Canada, with ≥ 80% of particles below 37 μm. (Author)

[en] Concentrations of 18 trace elements were determined in 40 samples of bottom sediments of Lake Baikal by instrumental neutron activation analysis. The absence of anthropogenic pollution of sediments by minor elements was found. The main geochemical peculiarities of Lake Baikal bottom sediments are enrichment by light rare earth elements (REEs) and a deficit of caesium and tantalum. The distribution of REEs in Lake Baikal bottom sediments is of a specific type that is intermediate between riverine and sea types. (author)

[en] The use of solvent extraction methods for the radiometric determination of boron is scarce. This work was undertaken to examine the feasibility of an indirect radiometric method for the determination of trace amounts of boron by solvent extraction. Mandelic acid was used as the complexing agent for boron and the complex anion formed was extracted as an ion associate with zinc-65-labelled bis(1,10-phenanthroline)zinc(II) into isobutyl methyl ketone. The activity of zinc in the organic layer was measured using an NaI-Tl well-type scintillation detector, and was a linear function of the concentration of boron in the aqueous phase over the range 0-10 μg in a final volume of 15 ml. A detection limit of 0.25 μg of boron in a 15 ml aqueous volume could be achieved. The interfering effect of various ions was overcome by selective distillation of boron as methyl borate. The method was applied to the determination of boron in Cr-Mo-B alloy, ointments, talcum powder and eye lotion samples. The reliability of the proposed method was checked by comparing the results obtained for the above samples with those given by ICP-AES. (author)

[en] Three radiometric methods for the determination of uranium in aqueous samples, involving the use of a liquid scintillation counter, have been studied and compared. Uranium is separated and purified by coprecipitation with iron(III) hydroxide followed by an anion-exchange process. The purified uranium in the eluate (0.1 mol 1^-1 HCl) can either be collected and stored and the Cerenkov radiation from the in-growth of the high-energy β-emitter ²³⁴Pa counted, or the uranium can be extracted from the chloride eluate into diethylhezylphosphoric acid in toluene containing appropriate scintillation materials and counted by a liquid scintillation technique. Alternatively, uranyl chloride can be converted into uranyl nitrate, which is then dissolved in 1 ml of 1,4 dioxan, and the solution is subsequently mixed with scintillation solution and counted. In the liquid scintillation methods, both ²³⁴U and ²³⁸U can be determined, but by using the Cerenkov method, ²³⁸U is measurable in isolation. Several variants of the chemical-separation procedure have been studied in relation to their effect on quenching, sensitivity and accuracy. The background count rates observed were 0.04, 0.075 and 0.213 counts s^-1 for the 1,4-dioxan, extraction and Cerenkov techniques, respectively; the lower limit of detection was taken as 3σ of the background. Chemical yields were in the range 80-90%. (Author)

[en] The possibilities for isotopic spectral gas analysis are considered. The method is based on a combination of an isotope dilution method (with or without further physico-chemical transformation of the resulting analytical mixture) and a spectroscopic measurement of the isotope composition of the element to be determined. The transformation includes various processes of isotope balancing, their accumulation and isolation. Detection limits for instrumental techniques are 100 ppb-10 ppt and for the combined techniques 1 ppm-1 ppb. Calibration of the method does not require reference gas samples based on the composition of the analysed gas. (Author)

[en] A simple radiochemical procedure has been implemented for neutron activation analysis of fluid inclusions in fluorite. Samples of 100 mg or less are irradiated in a thermal neutron flux of 1 x 10¹⁶ n m^-2 s^-1 before crushing and leaching with NaCl carrier solution. The solution is transferred with a filtered syringe and counted immediately for Na and Cl, and after at least 5h for Br. The recovery of the carrier is measured by re-irradiation of the sample. The detection limits are < 1 μg for Cl and Na, and < 10 ng for Br. (author)

[en] A radiochemical neutron activation analysis method was developed based on pyrolysis followed by double gold amalgamation for the determination of mercury in solid samples. Accurate results were obtained for mercury determinations in six standard reference materials of varying matrices certified for mercury, including coal. Linearity was demonstrated up to mercury concentrations of 10 000 ng g^-1. The method is capable of yielding precise, reproducible values with a detection limit of 5 ng g^-1 for mercury determination in coal. (author)