Positron annihilation lifetime spectroscopy of dodecaborate cage molecules in aqueous nitrate solutions

A fast-fast PALS spectrometer incorporating two BaF₂ scintillation detectors was characterized. The PALS spectrometer was employed to measure a model explosives system having nitrate oxidizing sites and B₁₂H₁₂ ^-2 reducing sites. Positron annihilation lifetimes and intensities were measured for nitrogen-purged aqueous solutions containing various concentrations of potassium dodecahydrododecaborate K₂B₁₂H₁₂ and potassium nitrate with added carrier-free ²²NaCl. Data analysis was accomplished using the PALSfit software program. The influence of electron scavenging and competition by nitrate ions was measured for various concentrations of potassium nitrate. Suppression of positronium formation by nitrate ions at 5 M concentration was greater for o-Ps than for p-Ps in 0.42 M dodecahydrododecaborate solution. At concentrations above 10^-2 M dodecahydrododecaborate only solutions the B₁₂H₁₂ ^-2 anion suppressed p-Ps formation.