Irradiation growth texture factor ($G_d=1-3⟨{\cos }^2\theta ⟩$)

In an ideal axisymmetric volume-conserving crystal grain model, directional growth is proportional to $1-3⟨{\cos }^2\theta ⟩$, where $\theta$ is the angle between that direction and the crystal c-axis. Random crystallographic texture has $⟨{\cos }^2\theta ⟩=1/3$.