Measurement of vapor pressures using X-ray induced fluorescence

►A new method for measuring vapor pressures has been demonstrated. ► The method is based on high-energy X-ray induced fluorescence. ► It is applicable to pressures on the upper end of the Knudsen cell range and higher. ► Measurements of the total densities of Dy over DyI3 and Tm over TmI3, and their corresponding vapor pressures are reported.