To produce an electron-positron pair, the minimum energy of γ-ray photon must be

Q: To produce an electron-positron pair, the minimum energy of γ-ray photon must be

(a) 1.02 keV

(b) 1.02 MeV

(c) 1.02 BeV

(d) 1.02 eV

Ans: (b)

Sol: Rest energy of electron = 9 .1 × 10^-31 × (3 × 10⁸)² J

= 81.9 × 10^-15 J

= 81.9 × 10^-15/(1.6 × 10^-13)

= 0.510 Me V

As mass of electron =mass of positron , hence rest mass energy is also equal .

γ → e^– + e⁺

Energy of photon = 2 × 0.51 = 1.02 Me V