Abstract: High efficiency X-ray irradiation device and method of using same comprising a transmission tube equipped with a high voltage cathode which faces an anode window. The anode itself is in the form of a thin metallic shell applied to the internal surface of a thin window which is transparent to X-ray radiation. The sample to be irradiated has an irradiation surface, which is placed opposite to and surrounds the face of the anode window. Both the window and the irradiation surface of the sample are formed by continuous surfaces. When performing the method, each of these surfaces is arranged such that if is bounded by a closed curve located in the plane which intersects the zone in which the window is attached to the tube envelope or casing.