The rest energy of an electron and its antiparticle,a positron,is 0.511 MeV.In order to produce an electron-positron pair,a gamma ray must have an energy larger than 1.022 MeV because of
A)time dilation.
B)length contraction.
C)the equivalence of mass and energy.
D)the principle of relativity.
E)none of the above.

Question

Quizplus · Accepted Answer

According to the principle of equivalence of mass and energy (E=mc²), the energy required to create a particle-antiparticle pair is equal to twice the rest energy of the particle, which in this case is 2(0.511 MeV) = 1.022 MeV. Therefore, a gamma ray with an energy larger than 1.022 MeV can create an electron-positron pair. The other options are not relevant in explaining this phenomenon.

The Rest Energy of an Electron and Its Antiparticle,a Positron,is