A method and apparatus for x-ray fluorescence measurement in object (1) are disclosed. The method includes (a) producing x-ray beam (2) using source device (10), wherein beam extends through object parallel to a first projection direction, (b) irradiating object with beam at scan positions in first projection plane, which are set by scanning device (20) such that source device and object are moved relative to one another, (c) detecting x-ray radiation emitted from object using detector array device (30) securely connected to source device and including spectrally selective detector elements (31) arranged to detect radiation, and stop lamellas (32) extending in radial directions relative to beam direction shielding detector elements from radiation scattered in object and arranged such that detector elements are able to detect radiation from all locations, and (d) processing detector signals to capture x-ray fluorescence of target particles in radiation and to localize target particles in object.