Three-photon annihilation of the positron with a negatron has been determined quantitatively as well as qualitatively by the simultaneous observation of the emitted photons with scintillation counters. The ratio of the reaction cross sections for two- and three-photon annihilation has been determined as $\frac{{\sigma }_{2k}}{{\sigma }_{3k}}=402\mathrm{}\pm 50$. This is in agreement with the theory of Ore and Powell but definitely differs from the theoretical values obtained by Lifshitz and by Ivanenko and Sokolov.

• Received 11 January 1954

DOI:https://doi.org/10.1103/PhysRev.96.691