Fig. 3

a Measured energy spectra of the primary X-rays from the Ge target for PIXRF (blue) and the X-ray tube for conventional XRF (green). The absorption characteristics of Cu as the sample element were plotted as a function of the X-ray energy (red). b Measured energy spectra of the primary X-rays from the Cu target for PIXRF (blue). The absorption characteristics of Co as the sample element were plotted, as well (red). The proton and electron charges shown in the ordinates indicate the total charges (current × time) of these particles impinged on the targets for PIXRF and the anode in the X-ray tube, respectively