Annihilation of Positrons in Organic Liquids

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Abstract
The mean life τ2 and fraction I2 of positrons which form 3S positronium have been measured for annihilation in 20 organic liquids—alcohols, glycols, acids, benzene derivatives, and others. By using the measured value of τ2, it is possible to calculate 〈σν〉Av where σ is the molecular cross section for annihilating 3S positronium on collision and ν is the velocity of the positronium atom. The results show that in general 〈σν〉Av is related to the ``size'' of the molecule although there are some consistent exceptions to this rule. There is also a rough correlation between τ2 and density, τ2 being shortest for the most dense liquids and longest for the least dense ones.