Calculated initial vacancy ratios (<em>I</em>_L = <em>I</em>_{{ m KL}^{1}}:<em>I</em>_{{ m KL}^{0}}), extrapolated x-ray intensity relative to the main line (<em>R</em>_L = <em>X</em>_{{ m KL}^{1}}:<em>X</em>_{{ m KL}^{0}}) and to the total intensity (<em>R</em>_T = <em>X</em>_{{ m KL}^{1}}:<em>X</em>_{{ m KL}^{0}+{ m KL}^{1}}), average differences in <em>X</em>_{{ m KL}^{1}} intensity between oxides and pure elements extracted from the literature (ΔR_L), and the product effect on the total x-ray yield

<p><b>Table 1.</b> Calculated initial vacancy ratios (<em>I</em>_L = <em>I</em>_{{\rm KL}^{1}}:<em>I</em>_{{\rm KL}^{0}}), extrapolated x-ray intensity relative to the main line (<em>R</em>_L = <em>X</em>_{{\rm KL}^{1}}:<em>X</em>_{{\rm KL}^{0}}) and to the total intensity (<em>R</em>_T = <em>X</em>_{{\rm KL}^{1}}:<em>X</em>_{{\rm KL}^{0}+{\rm KL}^{1}}), average differences in <em>X</em>_{{\rm KL}^{1}} intensity between oxides and pure elements extracted from the literature (ΔR_L), and the product effect on the total x-ray yield. Absolute uncertainties are listed in parentheses.</p> <p><strong>Abstract</strong></p> <p>Proton-induced x-ray emission (PIXE) was used to assess the accuracy of the National Institute of Standards and Technology XCOM and FFAST photo-ionization cross-section databases in the low energy region (1–2 keV) for light elements. Characteristic x-ray yields generated in thick samples of Mg, Al and Si in elemental and oxide form, were compared to fundamental parameters computations of the expected x-ray yields; the database for this computation included XCOM attenuation coefficients. The resultant PIXE instrumental efficiency constant was found to differ by 4–6% between each element and its oxide. This discrepancy was traced to use of the XCOM Hartree–Slater photo-electric cross-sections. Substitution of the FFAST Hartree–Slater cross-sections reduced the effect. This suggests that for 1–2 keV x-rays in light element absorbers, the FFAST predictions of the photo-electric cross-sections are more accurate than the XCOM values.