Patent Number: 
Section: claims

1. An X-ray fluorescence, XRF spectrometer, for measuring X-ray fluorescence emitted by a target, the XRF spectrometer comprising:an X-ray tube with an anode to emit a divergent X-ray beam;a capillary lens configured to focus the divergent X-ray beam on the target;an aperture system positioned between the anode of the X-ray tube and the capillary lens and comprising at least one pinhole; anda detector configured for detecting X-ray fluorescence radiation emitted by the target,wherein the at least one pinhole is configured for being inserted into the divergent X-ray beam and for reducing a beam cross section of the divergent X-ray beam between the anode and the capillary lens; andthe XRF spectrometer further comprising a control unit configured for adapting the focal depth dF of the XRF spectrometer by controlling the beam cross section of the divergent X-ray beam via the aperture system and based on a topography of the target and/or while scanning the target in at least one selected from among X- and Y-directions. 2. The XRF spectrometer of claim 1, wherein a front focal point of the capillary lens is placed at the anode. 3. The XRF spectrometer of claim 1, wherein the X-ray tube is a microfocus tube and/or wherein the XRF spectrometer is a micro XRF spectrometer. 4. The XRF spectrometer of claim 1,wherein the capillary lens has an entrance aperture, a front focal length, and a front aperture angle α that obey the equation:            tan      ⁢                          ⁢      α        =                  entrance        ⁢                                  ⁢        aperture        ⁢                                  ⁢                  (          11          )                            front        ⁢                                  ⁢        focal        ⁢                                  ⁢        length              ,and wherein the front focal length corresponds to a distance between the entrance aperture and the anode, and/orwherein the capillary lens has an exit aperture, a rear focal length, and a rear aperture angle β that obey the equation:            tan      ⁢      β        =                  exit        ⁢                                  ⁢        aperture        ⁢                                  ⁢                  (          12          )                            rear        ⁢                                  ⁢        focal        ⁢                                  ⁢        length              ,and wherein the rear focal length corresponds to the distance between the exit aperture and the target. 5. The XRF spectrometer of claim 1, wherein the aperture system comprises at least one pinhole of adjustable size. 6. The XRF spectrometer of claim 1, wherein the aperture system comprises a revolver or a slider, each with a plurality of pinholes of different sizes that are each configured for being individually inserted into the divergent X-ray beam. 7. The XRF spectrometer of claim 6, wherein the revolver or the slider further comprises at least one filter for spectrally modifying the divergent X-ray beam. 8. The XRF spectrometer of claim 6, further comprising an additional revolver or slider with at least one filter for spectrally modifying the divergent X-ray beam. 9. A method for adjusting the focal depth dF of an X-ray fluorescence, XRF, spectrometer comprising an X-ray tube with an anode to emit a divergent X-ray beam, a capillary lens configured to focus the divergent X-ray beam on a target, an aperture system positioned between the anode of the X-ray tube and the capillary lens and comprising at least one pinhole, and a control unit configured for controlling the aperture system and for performing the steps of:inserting one of the at least one pinhole in the divergent X-ray beam between the anode and the capillary lens;reducing a cross section of the divergent X-ray beam and a front aperture angle α of the capillary lens with one of the at least one pinhole;increasing the focal depth dF of the XRF spectrometer;estimating a required target focal depth based on a topography of the target; andsetting the focal depth dF of the XRF spectrometer based on the estimated target focal depth. 10. A method for adjusting the focal depth dF of an X-ray fluorescence, XRF, spectrometer comprising an X-ray tube with an anode to emit a divergent X-ray beam, a capillary lens configured to focus the divergent X-ray beam on a target, an aperture system positioned between the anode of the X-ray tube and the capillary lens and comprising at least one pinhole, and a control unit configured for controlling the aperture system and for performing the steps of:inserting one of the at least one pinhole in the divergent X-ray beam between the anode and the capillary lens;reducing a cross section of the divergent X-ray beam and a front aperture angle α of the capillary lens with one of the at least one pinhole;increasing the focal depth dF of the XRF spectrometer;scanning the target in at least one selected from among X- and Y-directions; andadapting the focal depth dF of the XRF spectrometer while scanning the target.