According to some aspects, a carrier configured for use with a broadband x-ray source comprising an electron source and a primary target arranged to receive electrons from the electron source to produce broadband x-ray radiation in response to electrons impinging on the primary target is provided. The carrier comprising a housing configured to be removeably coupled to the broadband x-ray source and configured to accommodate a secondary target capable of producing monochromatic x-ray radiation in response to incident broadband x-ray radiation, the housing comprising a transmissive portion configured to allow broadband x-ray radiation to be transmitted to the secondary target when present, and a blocking portion configured to absorb broadband x-ray radiation.
