Positron lifetimes in crystalline solids exposed to γ rays with energies above the electron–positron pair formation threshold and a weak magnetic field

Abstract

Abstract Theory predicts that positrons in crossed motional electric and magnetic fields form long-lived positronium in vacuum. It follows that binding of the electron to anions of dielectric solids may prevent fast annihilation by forming electric positron–electron dipole oscillators with lifetimes of hundreds of minutes. To test this hypothesis, lifetime distributions of time-coincident, 180° γ-rays from crystalline alkali halides and a polycyclic hydrocarbon were measured in 12 and 95 G magnetic fields. Gamma-ray sources with energies above the electron–positron pair formation threshold were used to make positrons.