Assume  that  an electron and  a  positron  pair  is  formed  from a  gamma-ray  photon  having energy  3.0  MeV.Find  the total kinetic  energy  (in Mev)  of  the  positron and the electron  that are   formed

Given that an electron and a positron pair are  formed from a gamma-ray photon.
${\gamma }^{\to }-1^{e^0+}+1^{e^0}$
The energy of the gamma-ray photon =3.0MeV.
From energy –mass equivalence, the energy released during the formation of the electron-positron pair 
$E=m_e{C}^2+m_e{C}^2=2m_e{C}^2=\frac{2\times 9.1\times {10}^{-31}\times {(3\times {10}^8)}^2}{1.6\times {10}^{-19}\times {10}^6}=1.02MeV$
$\Rightarrow$ The energy released during  this process=1.02MeV.
According to the conservation of energy in nuclear
Reactions, the remaining energy of the  gamma-ray photon will be in the form of the products.
The kinetic energy of the electron –positron pair 
$=-3-1.02=1.98MeV.$