The world’s roundest object is a perfect Silicon Sphere which currently holds the official weight of a kilogram in a physical form.
The Avogadro project aims to redefine Avogadro’s constant (currently defined by the kilogram — the number of atoms in 12 g of carbon-12) and reverse the relationship so that the kilogram is precisely specified by Avogadro’s constant. This method required creating the most perfect sphere on Earth. It is made out of a single crystal of silicon 28 atoms. The silicon was purified in ex-Soviet centrifuges once used to refine uranium for nuclear weapons. The centrifuges separated the silicon by isotope, allowing researchers to create a remarkably pure batch of silicon-28. To shape the spheres, the Australian Center for Precision Optics pulled optical engineer Achim Leistner out of retirement, who has been creating precision spheres for decades. The small-scale roughness of the balls varies by only 0.3 nanometres, and their curvature by 60 to 70 nanometres.
By carefully measuring the diameter, the volume can be precisely specified. Since the atom spacing of silicon is well known, the number of atoms in a sphere can be accurately calculated. This allows for a very precise determination of Avogadro’s constant.
No comments:
Post a Comment