Abstract: For volumetric analysis of the elemental composition of a measured sample (3) the method of three-dimensional scanning is executing using fluorescence induced by electromagnetic radiation, in which the primary beam (1) of electromagnetic radiation is flattened and is directed at the measured sample (3) in which it irradiates the measured area (6). From the measured area (6) there exits fluorescence radiation, which is almost completely shielded by the shielding means (7) to a secondary beam (9), which is released towards the shielded detector (4) through the permeable area (8) formed in the shielding means (7). The secondary beam (9) projects the image of the measured area (6) onto the shielded detector (4), which records the data of the measured area (6) and subsequently uses the data to obtain an elemental composition of the measured sample (3), including the distribution of concentration of elements in the sample volume.