Positronium lifetime in polymers
  A model describing the relationship between the ortho--positronium lifetime and the volume of a void, located in a synthetic zeolite, is analyzed. Our idea, which allows us to take into account the effects of temperature, comprises the introduction of a non--hermitian term in the Hamiltonian, which accounts for the annihilation of the ortho--positronium. The predictions of the present model are also confronted against an already known experimental result. 
Abel Camacho (Dept. of Physics, Universidad Autonoma   Metropolitana-Iztapalapa, Mexico, DF, Mexico)