N. A. Danilov

Performances and stability of a 2.4 ton Gd organic liquid scintillator target for bar nue detection

In this work we report the performances and the chemical and physical properties of a 2 1:2 ton organic liquid scintillator target doped with Gd up to 0:1%, and the results of a 2 year long stability survey. In particular we have monitored the amount of both Gd and primary uor actually in solution, the optical and uorescent properties of the Gd-doped liquid scintillator (GdLS) and its performances as a neutron detector, namely neutron capture eciency and average capture time. The experimental survey is ongoing, the target being continuously monitored. After two years from the doping time the performances of the Gd-doped liquid scintillator do not show any hint of degradation and instability; this conclusion comes both from the laboratory measurements and from the in-tank measurements. This is the largest stable Gd-doped organic liquid scintillator target ever produced and continuously operated for a long period.

Extraction methods in development of Gd-loaded liquid scintillators for detection of low-energy antineutrino: 1. gadolinium extraction with carboxylic acids

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.

Physicochemical study of linear alkylbenzene as base component for scintillation neutrino detectors

Properties of domestic linear alkylbenzene were subjected to a physicochemical study in order to enable use of this compound as the main solvent in large-volume liquid organic scintillators intended for neutrino experiments. New compositions of Gd-containing liquid scintillators based on linear alkylbenzene were suggested and examined.

Measuring the C-14 isotope concentration in a liquid organic scintillator at a small-volume setup

A low-background scintillation setup situated in the Gran Sasso National Laboratory is described. The facility is composed of nine identical cells, each 2 L in volume. The 14C content of a PXE-based scintillator has been measured using this setup; the value obtained is R(14C/12C) = (12.6 ± 0.4) × 10−18. This result can be used for comprehensive investigation of possible 14C production channels in organic scintillators.

Exhaustive removal of thorium and uranium traces from neodymium by liquid extraction

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 <10 ppt Th and 31 ppt U (detection limit 10 ppt) was obtained. By semicountercurrent extraction, from the initial aqueous NdCl3 solution containing 200 ppb Th, the raffinate containing <10 ppt Th was obtained in one extraction step. The results obtained confirm the possibility of exhaustive removal of Th and U impurities (to the level of ≤1 ppt) from Nd by extraction with TOPO solutions from chloride solutions.

Scintillators Based on Ytterbium Chloride Adducts with Neutral Organophosphorus Extractants for Detecting Solar Neutrino for LENS (Low-Energy Neutrino Spectroscopy) Experiment

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.

Extraction of Mineral Acids with Neutral Organophosphorus Extractants

Extraction of HNO3, HCl, H2SO4, H3PO4, H3AsO4, HF, and H2C2O4 with triisoamyl phosphate (TiAP), diisooctyl methylphosphonate (DiOMP), isoamyldialkyl(C7-C9)phosphine oxide (DRPO), and cyclohexyldialkyl(C7-C9)phosphine oxide (DRPO-1Ts) was studied, and the extraction isotherms were obtained. The solvation numbers of certain acids and extractants were determined by dilution and saturation methods. Purification of wet-process phosphoric acid to remove arsenic was studied. Distribution of Cu, Zn, Ni, Co, Fe, and Mn microamounts in the oxalic acid-neutral organophosphorus compound (NOPC) extraction systems was measured, and the feasibility of purification of oxalic acid to remove these metals to a 10-7% content was demonstrated.

A Nd-loaded liquid organic scintillator for the experiment aimed at measuring double β decay

A new Nd-loaded liquid organic scintillator based on pseudocumene (PC) solvent was developed for the experiment aimed at searching for 0νββ decay of a 150Nd nucleus. The optical characteristics of the scintillator were measured for several Nd concentrations. The measurements taken using two modules 1 and 2 m in length have made it possible to determine the effective attenuation length of the PC scintillator containing Nd (6.5 g/L). It was demonstrated that the scintillator characteristics remained unaltered over 1 year. The content of radioactive contaminants was analyzed, and the sensitivity of the experiment to effective Majorana neutrino mass 〈mν〉 ∼ 0.05–0.10 eV was estimated for a detector containing a 12-ton scintillator.

Formation of coordination compounds in gadolinium-loaded liquid organic scintillators (GdLS): Use of mixed-ligand gadolinium complexes in GdLS preparation

The formation of coordination compounds between gadolinium 2-methylvalerate (Gd(2MVA)3) and trioctylphosphine oxide (TOPO) in a gadolinium-loaded liquid scintillator (GdLS) solution was studied by MALDI-TOF MS. The most abundant gadolinium-containing compound in the GdLS solution in the presence of TOPO is the monomer complex Gd(2MVA)3 · (TOPO)2. In the absence of TOPO, the solution contains only Gdn(2MVA)3n (n = 2–5) association species. Therefore, TOPO prevents carboxylate polymerization in the solution and can be used as a stabilizer of the gadolinium compounds in GdLS. The existence of the Gd(2MVA)3 · TOPO complex is confirmed by IR spectroscopy. The possibility of coordination between Gd(2MVA)3 and 2,5-diphenyloxazole (PPO), the most common scintillation admixture, has been investigated. No complexes between Gd(2MVA)3 and PPO have been detected by MALDI-TOF MS in the scintillator solution. IR spectroscopic data also do not provide any unambiguous indication of coordination between Gd(2MVA)3 and PPO.

Extraction methods in development of Gd-loaded liquid organic scintillators for antineutrino detection: 2. Scintillators based on solutions of gadolinium 2-methylvalerate

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