Calibration of PIXE yields using Cu as a reference

We have evaluated a systematic deviation from unity of the relative correction factor, h, for calibration of the X-ray yields in particle induced X-ray emission (PIXE). For this, we estimated the values of h for various elements in the range 22 ≤ Z ≤ 79, and with Cu as a reference material. The value of h for the elements with a characteristic X-ray energy <20 keV is close to one with an accuracy of 5%. The uncertainty on the h values is comparable to the uncertainty of the ionization cross sections and fluorescence yields.