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

Abstract

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 Gd n (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.