Hyperfine energy splitting of positronium measured in water

TLDR: For the positronium-free atom in the ground state, the hyperfine structure energy splitting is ΔW0, 0, 8.34, 1.5, 12.5 kG.

Abstract: In order to investigate the behavior of positronium in water, magnetic quenching measurements have been performed at various temperatures from 0 to 45 °C and with applied fields up to 12.5 kG. From these measurements it has been possible to evaluate the effect of the water. In fact, while for the positronium-free atom in the ground state the hyperfine structure energy splitting is ΔW0 = 8.34 × 10−4 eV, for positronium in water we find two consistent values, ΔW = (6.32 ± 0.20) × 10−4 eV and ΔW = (7.30 ± 0.80) × 10−4 eV, obtained by considering the magnetic-field effect on the positronium component which decays by pickoff and on its decay rate.