Effect of paramagnetic particles on the lifetime of o-Ps in positron spur

Abstract

The effect of paramagnetic molecule O 2 on the lifetime of o-Ps in different kinds of organic liquids (benzene, cyclohexane and hexafluorobenzene) was studied. The spur processes are quite different in these three liquids. In pure benzene, the triplet excited molecule ( 3M ∗) in the positron spur can quench o-Ps. In cyclohexane the active radicals are the main particles which quench o-Ps. In hexafluorobenzene both the radicals and triplet excited molecules can quench o-Ps, but the last is more important. The rate constants of the reaction between O 2 and o-Ps measured in benzene, cyclohexane and hexafluorobenzene are 3.41 × 10 10 M −1 s −1, 2.93 × 10 10 M −1 s −1 and 2.97 × 10 10 M −1 s −1, respectively. By analysing the experimental results, a more realistic value of pick-off annihilation lifetime of o-Ps in these three liquids was obtained.