Positronium bubble oscillation in room temperature ionic liquids

Abstract

Positronium bubble oscillation before the stabilization of the bubble was successfully observed by the change of the triplet Ps (ortho-Ps) pick-off annihilation rate in a room temperature ionic liquid, N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI). It was reported that the Ps bubble stabilization in TMPA-TFSI took more than 500 ps. For materials having Ps formation, singlet Ps (para-Ps) gives the fastest annihilation mean lifetime of about 125 ps. Although it is intrinsic annihilation, the Ps bubble oscillation affects the para-Ps annihilation rate. The oscillation on the ortho-Ps pick-off annihilation was expected to appear at positron ages older than about 400 ps after the para-Ps annihilation fraction becomes small enough. An oscillation with 5.85 GHz frequency of the ortho-Ps pick-off annihilation rate was successfully observed at the positron ages older than 500 ps in 25 ◦C TMPA-TFSI.