A sample inspection apparatus includes a source of electromagnetic radiation, a beam former for producing a plurality of coaxial and substantially conical shells of radiation, a detection surface and a set of conical shell slot collimators. Each conical shell has a different opening angle. The detection surface is arranged to receive diffracted radiation after incidence of one or more of the conical shells upon the sample to be inspected. The set of conical shell slot collimators is provided at or close to the detection surface which each stare at different annular regions of different corresponding conical shells.