What is Nuclear spin quantum number, gyromagnetic ratio?

A nucleus has a spin angular momentum of quantum number $I$, its nuclear spin quantum number ($I = 0$ for $\ce{^{12}C}$, $\ce{^{16}O}$; $\frac12$ for $\ce{^1H}$, $\ce{^{13}C}$, $\ce{^{15}N}$, $\ce{^{19}F}$, $\ce{^{31}P}$; 1 for $\ce{^2H}$, $\ce{^{14}N}$), and a magnetic moment $\boldsymbol\mu = \gamma\hat{\mathbf I}$ proportional to it; $\gamma$ is the gyromagnetic ratio. Along a field $B_0$ (axis $z$), $\hat I_z$ takes the values $m_I\hbar$, $m_I = -I, \dots, I$.