Retraction bellows

To protect the sample from stray electrons from the anode, from heating effects, and from possible contamination by the source enclosure, a thin (-2 pm) window of aluminum foil is interposed between the anode and the sample. For optimum X-ray photon flux on the surface (i. e. optimum sensitivity), the anode must be brought as close to the sample as possible, which means in practice a distance of -2 cm. The entire X-ray source is therefore retractable via a bellows and a screw mechanism. 

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