If $\left| {\overrightarrow a } \right| = 4,\left| {\overrightarrow b } \right| = 2$ and the angle between ${\overrightarrow a }$ and ${\overrightarrow b }$ is $\pi /6$ then ${\left( {\overrightarrow a \times \overrightarrow b } \right)^2}$ is equal to :