Current determination of Avogadro's constant

The Avogadro project aims to redefine the kilogram by evaluating the number of atoms in a spherical volume, to the nearest atom. The aim is to manufacture a sphere of silicon 28, whose lattice regularity enables precise evaluation of the number of atoms per unit volume.

This method has the distinct advantage of presenting the general public with a palpable object representing the kilogram. It is also easier to grasp than the complex Watt balance. From a scientific point of view, it should be noted that this project is the result of even closer cooperation between national research organizations than in the case of the Watt balance, insofar as the various elements leading to the creation of the silicon sphere are carried out in laboratories all over the world (Australia, Japan, Italy, Sweden...).

Silicon is preferred to carbon because the...