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The efficiency of removing U and Th from a liquid organic scintillator based on linear alkylbenzene (LAB) by stripping with a 0.02 M aqueous solution of aminomethylenediphosphonic acid and by sorption on aluminum oxide and silica gel was studied. A procedure was developed for purification of scintillation additives (2,5-diphenyloxazole, 2-biphenyl-5-phenyloxazole, p-terphenyl) to remove 40K.

A procedure was developed for removing uranium, thorium, and potassium from a liquid organic scintillator based on linear alkylbenzene (LAB) by stripping with water. The volume ratio of the scintillator and water in the process should be no less than 1: 5. The attenuation length (L 420) of LAB after treatment with water does not change and is as high as 13.0 ± 1.8 m. The solubility of water in LAB and of LAB in water was determined to be 46 and 5.1 ppm, respectively.

The Th content in commercially available Nd2O3 samples with the main substance content of 99.0–99.998% was found to be 2–8, and that of U, 3–230 ppb. Therefore, to obtain Nd meeting the requirements of the experiment on studying neutrinoless double β-decay, it should be purified to reduce the content of Th and U impurities by a factor of 103–104. To this end, the extraction of Nd, Th, and U from hydrochloric acid media with solutions of trioctylphosphine oxide (TOPO) in toluene was studied. The distribution ratios of Th increase with a decrease in the HCl concentration in the initial aqueous solution. With an increase in the Cl− concentration in the aqueous phase, the U distribution ratios decrease, probably because of a decrease in the concentration of the free extractant due to the extraction of Nd and HCl. On the contrary, the distribution ratios of Th increase with an increase in the Cl− concentration in the aqueous phase, with the slope of the straight line in the coordinates logDTh-log[Cl−]aq close to 7, which may be due to coextraction of Th with Nd in the form of the complex ThNdCl7. The enthalpies of formation of the extractable complexes of Th and U were determined from the temperature dependence of the extraction of Nd, Th, and U chlorides with a 0.1 M solution of TOPO in toluene. The optimal extraction system was chosen for Nd purification to remove traces of Th and U: organic phase, 0.1 M solution of TOPO in toluene; aqueous phase, 2.4 M NdCl3 + 0.1 M HCl. From the initial aqueous solution contaning 574 ppt Th and 2837 ppt U, by single extraction with an equal volume of 0.1 M TOPO in toluene, an aqueous solution containing

Complexes of Gd with carboxylic acids C4–C9 were prepared, and their properties were studied: solubility in water and organic solvents in relation to temperature, melting points, and decomposition points. A procedure was developed for removing water from gadolinium 2-methylvalerate Gd(2MVA)3 to a final content not exceeding 0.01%. To increase the solubility of Gd(2MVA)3 in low-polarity organic solvents and to stabilize the resulting organic solutions, it was suggested to add extractants such as 2-methylvaleric acid (H2MVA) or neutral organophosphorus compounds: triisoamylphosphine oxide (TIAPO) or trioctylphosphine oxide (TOPO). Liquid Gd-loaded organic scintillators based on Gd(2MVA)3 solutions with additions of H2MVA, TIAPO, and TOPO in trimethylbenzene (TMB), phenylxylylethane (PXE), and their mixtures with dodecane were prepared. Long-term tests (up to 2 years) of the stability of the optical properties of the scintillators obtained proved their stability at temperatures of up to 30°C. At elevated temperatures (40°C and higher), the scintillators degrade. The previously made suggestion that water in the scintillator negatively affects its optical properties in prolonged storage was confirm

Extraction of In with solutions of 2-methylvaleric acid (H2MVA) in trimethylbenzene (TMB) was studied. Depending on pH of the equilibrium aqueous phase, the extracted indium species are In(2MVA)3 · 3(H2MVA), In(2MVA)3, [In(2MVA)x(OH)3−x]n, etc., where 2MVA is the 2-methylvalerate anion and n is the degree of polymerization. By the extraction method, In-containing liquid organic scintillators (LOSs) with the following parameters were obtained: [In] = 50–96 g l−1, transparency 2–3 m, light output 68% relative to TMB. Long-term precision trials of the scintillators in the Gran Sasso underground laboratory (Italy) confirmed that the scintillator parameters were stable and met the requirements of the LENS experiment. A procedure was developed for preparing solid anhydrous indium hydroxycarboxylates, and their properties were studied. LOSs based on solutions of solid indium hydroxycarboxylates in TMB were prepared and subjected to long-term trials in which the transparency and light output were monitored. One of the major factors responsible for the instability of indium-containing LOSs is the presence of water in the organic phase.

A comparison was made of the properties of solvents meeting the requirements posed on Gd-loaded organic liquid scintillators (transparency, light output, compatibility with the structural materials of the detector). The optical properties of the solvents were examined in relation to various factors (purity of the initial reagents, concentrations of Gd and scintillation additives). Extraction of Gd with C4 C8 carboxylic acids was examined. The composition of the extractable Gd complexes with 2-methylvaleric and 2-ethylhexanoic acids, GdR3·3HR·mH2O (where m = 1–2, depending on the solvents used), was determined. The solubility of water in 2-ethylhexanoic and 2-methylvaleric acids was examined. Scintillators based on Gd 2-methylvalerates have better parameters than those based on the other carboxylic acids tested. The instability of the optical properties of the Gd carboxylate solutions is presumably due to the presence of water in the scintillator. Possible methods of water removal from the organic phase were discussed.

The physicochemical properties of C4-C8 carboxylic acids (mutual solubility of carboxylic acids and water, ionization constants in water, distribution between water and 1,2,4-trimethylbenzene, dimerization constants in 1,2,4-trimethylbenzene) were studied. Since indium carboxylates are sparingly soluble in 1,2,4-trimethylbenzene and the second organic phase is formed in the system, In-containing scintillators can be prepared from C4-C5 acids only in the presence of neutral organophosphorus compounds. The best results were obtained with an extracting agent containing isovaleric acid (C5) and 0.25 M triisoamylphosphine oxide. The scintillator prepared in this system contained 80 g l−1 In and had a transparency of up to 2 m and a 40% light output. These parameters did not change when the sample was stored in tightly sealed dark glass vessels for 2 years at 12–34°C in an argon atmosphere. Acids C6-C8 can be used for In extraction without organophosphorus additives. The best results were obtained with methylvaleric acid (H2MVA, C6). The correlation between the transparency and light output of the scintillators, on the one hand, and the preparation conditions, on the other hand, was studied. The properties of scintillators prepared from solutions of polymeric indium hydroxy-2-methylvalerates in 1,2,4-trimethylbenzene { [In(2MVA)0.8(OH)2.2] n (n = 9–115)} were the best. A procedure for extracting indium hydroxycarboxylates and preparing scintillators suitable for LENS experiment was developed. Scintillators with a volume of 4 1, an In concentration of 50 g l−1, a light output more than 65%, and a 3-m transparency were prepared.

The main features of extraction of ytterbium chloride with dibutyl butylphosphonate (DBBP) and triisoamylphosphine oxide (TIAPO) were studied. The effects of temperature, DBBP and TIAPO concentrations in 1,2,4-trimethylbenzene (TMB), and concentrations of salting-out agents LiCl and NH4Cl and mineral acid (HCl) on the ytterbium distribution coefficient were determined. The isotherms of extraction of HCl and YbCl3 with 50% DBBP and TIAPO in TMB were obtained. The composition of the extractable complexes of ytterbium chloride with DBBP and TIAPO (S), YbCl3·3S, was determined by saturation and dilution methods. The saturation of 50% solutions of DBBP and TIAPO in TMB with ytterbium chloride was modeled. Two samples of scintillators with ytterbium concentration of 90 g l- 1 were prepared, and their physical parameters were measured. The stability of sample properties was tested for 18 months.