Effect of Paramagnetic Impurity on the Long Lifetime of Positron in Liquid Ammonia

Abstract

We have computed the paramagnetic quenching effect of lithium and sodium in liquid ammonia on the long-lifetime component of positron annihilation. The triplet-to-singlet conversion cross sections, calculated in the Born approximation, turn out to be 5.9×${10}^{-14\mathrm{}}$ ${\mathrm{cm}}^2$ for Li and 7.2×${10}^{-14\mathrm{}}$ ${\mathrm{cm}}^2$ for Na for thermalized positronium. Reasonable agreement with the meagre existing experimental data is obtained.