Question

When an energetic $\gamma$-ray photon falls on heavy substance, an electron and positron produced. The least energy required for t process is

• A. 4.8 MaV
• B. 1.02 MeV
• C. 7.3 MeV
• D. 10 MeV

Answer 1

Answer: (B)

1.02 MeV

This phenomena is known as pair production
$hv{\to }_{+1}{\beta }^0+{\beta }^o$
Least energy required is
$E=2m{c}^2$
$E=2\times 9.1\times {10}^{-31}\times (3\times {10}^8{)}^2$
$E=1.64\times {10}^{-13}J$
$E=\frac{1.64\times {10}^{-13}}{1.6\times {10}^{-19}}=1.02MeV$