In the News … very interesting ..
Accurate Avogadro constant may help redefine the kilogram
A redefining of the kilogram is considered necessary because since 1889 the international standard is based on the weight of a cylinder of 90% platinum and 10% iridium stored under glass in a vault at the International Bureau of Weights and Measures in Paris, France. The problem is the cylinder (and its six copies) gains weight from dust despite all the precautions against this, and then loses it again when subjected to a steam bath to remove the dust. It also seems to be gaining about 50 micrograms in weight per century, so scientists would prefer a definition that is defined by reference to a constant.
A new accurate determination of the Avogadro constant has used the method of "counting" the atoms in a 1 kg sample of an almost perfect silicon sphere highly enriched with the isotope 28Si. They used isotope dilution mass spectroscopy to determine the molar mass of the silicon with unprecedented accuracy, and this enabled them to obtain the most accurate value for the Avogadro constant ever obtained.
I know they've been wrestling with this problem for many years now .. Australian Scientists were involved in the creation of the Silicon sphere. The smoothness of it is truly amazing …
if the spheres were enlarged to the size of the Earth, the highest hill would stand less than three meters tall.