Ndependence of coherent radiation from crystals

The total intensity averaged over all angles of short-wavelength radiation either scattered or spontaneously emitted nearly isotropically from each of a system of N radiators or scatterers is shown to vary linearly with N for large N. Although coherent effects can give intensities proportional to ${\mathrm{N}}^2$ in certain directions (e.g., Bragg angles), this enhancement is mainly at the expense of radiation otherwise emitted in other directions and does not appear in the overall angular distribution.