Abstract: Disclosed is a scanning x-ray fluorescence spectrometer for measuring accurately the content of a randomly distributed element contained in a sample. Said device comprising a linear excitation source of radioactive material in a holder which produces a beam of ionizing radiation capable of exciting the emission of primary x-rays of the said element from said sample. The sample is mechanically drawn through said beam in a direction perpendicular to the axis of said source, thus exposing the entire sample to a uniform radiation flux. A linear radiation detector is positioned on a plane parallel to said sample and said source, positioned such that its sensitive area faces said sample at the point where the most intense portion of said beam passes through said sample, thus achieving a uniform collection of x-rays from the sample.