In the first Born approximation for a delta-function potential \( V_{\vec{r}} = g \delta^3(\vec{r}) \), the scattering amplitude is proportional to the Fourier transform of the potential. For a spherically symmetric potential such as \( \delta^3(\vec{r}) \), the differential cross section \( \frac{d\sigma}{d\Omega} \) is independent of both the scattering angles \( \theta \) and \( \phi \), since the delta-function potential is rotationally invariant. This results in an isotropic scattering cross section.