With X-rays produced by protons exciting elemental and compound targets the mass attenuation coefficients have been systematicaJly measured for SiH4 in the range of X-ray energy 1.486-15.165keV, for Si in 8.041-29.109keV. Not only the validity of Bragg's additivity law in the gaseous compound was verifed by experiment, but also the mass attenuation coefficients of Si in the energy range 1.4-6 keV were obtained. The photoelectric cross sections have been obtained by subtracting thermal diffuse scattering and Compton scattering cross section from the measured total cross sections and compared with the theoretical results.