Question

A gamma ray photon creates an electron-positron pair. If the rest mass energy of an electron is 0.5 MeV and the total kinetic energy of the electron-positron pair is 0.78 MeV, then the energy of the gamma ray photon must be

• A. 0.78 MeV
• B. 1.78 MeV ​
• C. 1.28 MeV ​
• D. 0.28 MeV

Answer 1

The correct option is B 1.78 MeV ​

Energy of $\gamma$ -rays photon =rest mass energy + kinetic energy= 0.5 + 0.5 +0.78 = 1.78 MeV