Reactions between ortho-positronium and spur reactants in water

Hirade, Tetsuya  ; Oka, Toshitaka   

Pick off annihilation lifetime of ortho-positronium (o-Ps) depends on the size of the bubble formed by the positronium itself. The lifetime is longer at higher temperatures, because of the larger bubble size. However, only water shows reversed temperature dependence and it is considered that there exist more reactions of o-Ps with spur reactants at higher temperatures. Here, we tried to obtain the experimental evidence of these reactions of o-Ps by use of Age-Momentum Correlation measurement of annihilation -rays (AMOC). Obtained S(t) curves indicated in Fig.2 show that there were larger S values for higher temperatures at older positron age region. Larger S values indicate that there exist more spin conversion reactions of o-Ps.