An electron-ositron pair can annihilate with the emission of two $\gamma$-rays. A single (isolated) $\gamma$-ray cannot disappear with the creation of an electron-positron pair because
A) momentum could not be conserved.
B) energy could not be conserved.
C) angular momentum could not be conserved.
D) Hold it! The premise is wrong: a single (isolated) $\gamma$-ray can disappear under the circumstances described.

Question

Quizplus · Accepted Answer

A single (isolated) gamma-ray cannot create an electron-positron pair in empty space because momentum conservation would be violated. The initial momentum of the gamma-ray cannot match the combined momentum of the electron and positron, which would move in opposite directions.

An Electron-Ositron Pair Can Annihilate with the Emission of Two γ\gammaγ

An Electron-Ositron Pair Can Annihilate with the Emission of Two $\gamma$