Question

Electron-positron pair man be created by $\gamma$ rays. In this process the minimum energy $\gamma$-rays should be -

• A. $5.0MeV$
• B. $4.02MeV$
• C. $15.0MeV$
• D. $1.02MeV$

Answer 1

The correct option is D $1.02MeV$

An electron positron pair can be created by r rays. This phenomena is called pair production. The minimum energy that must be possessed by r rays for the same is the rest mass-energy possessed by the particles.

Electrons and positron have same mass.

So, total mass energy

$E=E_{e^{-}}+E_{e^{+}}$

$=2me{C}^2$

$=2\times 9.1\times {10}^{-31}\times (3\times {10}^8{)}^2$

$=1.638\times {10}^{-13}J$

$E=\frac{1.638\times {10}^{-13}}{1.6\times {10}^{-19}}=1.022$MeV

This is the minimum energy r rays should possess.