Abstract: The invention relates to a measuring element for a portable micro-X-ray spectrometer, said element comprising a radiation protected housing, at least an X-ray source, a detector, cooling parts for the detector and means for activating the X-ray source and the detector. In accordance with the invention, in order to advantageously guide the X-rays obtained by the X-ray source away from the radiation protected housing (1), at least one capillary tube (3) has been mounted in the X-ray source (4), said capillary tube (3), at the opposite end of the tube as seen from the X-ray source, being connected to a hole formed in the detector (5) for conducting the X-rays out of the radiation protected housing (1). The inner section of the capillary tube (3) is smaller at the end which, seen from the X-ray source, is opposite than at the end at the X-ray source (4).