Angular Correlation of Photons from Positron Annihilation in Light Metals

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Abstract
The angular correlation of gamma rays from positron annihilation in the light metals, Li, Be, Na, Mg, Al, K, and Ca, has been measured. The deviation of the two photons from colinearity is a measure of the total momentum of the annihilating electron-positron pair. If it is assumed that the positrons are thermalized before annihilation and that they annihilate only with electrons of a Sommerfeld free electron gas, the experimental results may be used to determine the Fermi energy of these electrons. It is interesting that the Fermi energies so determined are in good agreement with calculated values.