 Because of its low atomic number and very low absorption for X @-@ rays , the oldest and still one of the most important applications of beryllium is in radiation windows for X @-@ ray tubes . Extreme demands are placed on purity and cleanliness of beryllium to avoid artifacts in the X @-@ ray images . Thin beryllium foils are used as radiation windows for X @-@ ray detectors , and the extremely low absorption minimizes the heating effects caused by high intensity , low energy X @-@ rays typical of synchrotron radiation . Vacuum @-@ tight windows and beam @-@ tubes for radiation experiments on synchrotrons are manufactured exclusively from beryllium . In scientific setups for various X @-@ ray emission studies ( e.g. , energy @-@ dispersive X @-@ ray spectroscopy ) the sample holder is usually made of beryllium because its emitted X @-@ rays have much lower energies ( ~ 100 eV ) than X @-@ rays from most studied materials . 
