Question

Calculate the maximum wavelength of γ-rays which in passing through matter, can lead to the creation of electrons.

Answer 1

The minimum photon energy required for the e⁻e⁺ pair production is 2mc, 

where m is the mass of electron. Therefore 

hν = 2mc² = 2 × 0.511 = 1.022 MeV 

The corresponding wavelength 

λ = (1, 241/1.022 × 10⁶eV) nm = 1.214 × 10⁻¹²m