Measurement of Density Inhomogeneity for Source Masses in Time-of-Swing Method of Measuring

A method with scanning electron microscopy (SEM) is presented to measure the density inhomogeneity of the stainless steel (SS316) sphere prepared for measuring G using time-of-swing method. The experimental result shows that the relative density inhomogeneity of the sphere is better than 5.9×10^-4 over the volume of 0.272×0.234×0.005mm³. If we assume that the density inhomogeneity of the spheres used in our G measurement is the same as that of the sphere destroyed in testing, it will contribute to G value with an uncertainty of less than 0.034ppm in our G measurement. Furthermore, the mass centre offset from the geometric centre of the sphere will be less than 4.3×10-4,μm due to this inhomogeneity.