Abstract
A summary of the procedures used to certify NBS Standard Reference Material 1960, nominal 10-μm “space beads,” is presented. Three independent micrometrology techniques were used, with the results agreeing to about 0.1%. Center distance finding, a method based on optical microscopy, gave a value of 9.89 ± 0.04 μm, which was chosen as the certified mean diameter. Two supporting measurements, made using metrology electron microscopy and resonance light scattering, yielded mean diameters of 9.886 ± 0.029 and 9.898 ± 0.029 μm, respectively. The main peak of the size distribution for this material is nearly Gaussian, with a certified standard deviation of 0.09 μm, excluding outlying particles. The SRM 1960 microspheres were grown in microgravity aboard the NASA space shuttle “Challenger,” making the material the first commercial product to be made in space.
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