Numbers

The convenient unit of energy (mass and momentum too) is the electron volt.

$$\bgroup\color{black}1 eV = 1.602 \times 10^{-12} \mathrm{erg}=1.602 \times 10^{-19} \mathrm{Joule}\egroup$$

Use the fine structure constant to avoid CGS units which are used in the textbook.

$$\bgroup\color{black}\alpha = {e^2\over \hbar c} = 1/137\egroup$$

This combination saves a lot of work.

$$\bgroup\color{black}\hbar c = 1973 \mathrm{eV \AA} = 197.3 \mathrm{MeV F}\egroup$$

$$\bgroup\color{black} 1 \AA = 1.0 \times 10^{-10} \mathrm{m}\egroup$$

$$\bgroup\color{black} 1 \mathrm{Fermi} = 1.0 \times 10^{-15} \mathrm{m}\egroup$$

The Bohr radius gives the size of the Hydrogen atom.

$$\bgroup\color{black} a_0 = {\hbar\over \alpha m_e c} = 0.529 \times 10^{-10} \mathrm{m}\egroup$$

$$\bgroup\color{black}m_p = 938.3 \mathrm{MeV/c}^2\egroup$$

$$\bgroup\color{black}m_n = 939.6 \mathrm{MeV/c}^2\egroup$$

$$\bgroup\color{black}m_e = 0.511 \mathrm{MeV/c}^2\egroup$$