By default, the incident beam is perfectly monochromatic and collimated.
Here we show how to set finite distributions of wavelengths and of incident angles.
The wavelength follows a log-normal distribution around the mean value of 0.1 nm with a scale parameter equal to $0.1$.
Both incident angles follow a Gaussian distribution around the average values $\alpha_i = 0.2 ^{\circ}$ and $\varphi_i = 0^{\circ}$, respectively and $\sigma_{\alpha_i} = \sigma_{\varphi_i} = 0.1^{\circ}$.
The DWBA simulation is shown for a standard sample model:
The sample is composed of monodisperse cylinders deposited on a substrate.
The cylinders are dilute and distributed at random,
hence there is no interference between scattered waves.