Abstract With X-rays produced by protons exciting elemental or compound targets, the mass attenuation coefficients have been systematically measured for SiH 4 in the range of X-ray energies 1.486–15.165 keV, for Si between 8.041 keV and 29.109 keV. Not only the validity of Bragg's additivity law in the gaseous compound was verified by experiment, but also the mass attenuation coefficients of Si between 1.4 keV and 8 keV were obtained. The photoelectric cross sections have been obtained by subtracting the thermal diffuse scattering and Compton scattering cross sections from the measured total cross sections and compared with the theoretical results.