Positronium in Room Temperature Ionic Liquids

Positronium (Ps) bubble oscillation was observed in room temperature ionic liquids (RTILs). The frequency of the oscillation was quite stable up to positron age of 1-1.5 ns and the oscillation could be reproduced by the cosine curve from the positron age of zero. It indicated that the oscillation was caused by the repulsive force of the structure by ionic interactions and that Ps formation was occurred in very short time as 10-20ps like in usual liquids such as water. Therefore it was possible to conclude that the precursors of Ps, i.e. freely moving excess electrons and positrons, were solvated or pre-solvated within very short time in RTILs. Temperature dependence of the ortho-Ps pick off annihilation lifetime was very small in RTILs. Ps bubble size might not be affected by the surface tension of RTILs. The size of the non-ionic parts where Ps bubble forms in RTILs probably affects the Ps bubble size.