a) a continuous spectrum consisting of bremsstrahlung ("braking radiation") and
b) emission lines characteristic for electronic transitions caused in the anode material. The characteristic X-ray emissions, which are important for crystallography, have an intensity that is several orders of magnitude higher than the bremsstrahlung. The Ka1 and Ka2 components of the X-rays emission are cut out from the bremsstrahlung and other emission lines by filters, monochromators or X-ray mirrors, and the resulting monochromatic X-rays are collimated and focused onto the crystals. When X-rays are produced by a rotating anode, the cathode and anode are housed under vacuum, in which the anode target rotates at high speed to efficiently distribute and dissipate heat. The wavelength of an in-house source such as a tube or rotating anode generator is fixed by the choice of anode target material and not tunable, as is the case at a synchrotron, and the intensity of the source is less than that of a synchrotron.