Scientists at the German National Metrology Institute in Braunschweig said they are attempting to develop a new, pure silicon sphere 10-centimeters (four inches) in diameter as a standard of measure to replace the existing one.

Currently, a kilogram -- which is equal to 1,000 grams -- corresponds to the mass of a platinum-alloy cylinder stored in a highly protected vault in Sevres, just outside of Paris.

The problem is that the prototype of the kilogram is gradually losing weight, and scientists cannot explain why.

Counting atoms

Now, researchers are turning to the weight of silicon atoms to create a standard measure for the kilogram.

"We want to count the atoms, but we can't count one by one," Peter Becker, who leads the project, told the AFP news agency. "So we have to use some kind of trick, and the trick is to have a perfect structure where we know where all the atoms are."

Researchers said they will be able to calculate all the atoms in the new, more stable silicon container, which was produced in Russia, Australia and Germany, and that by knowing the exact number of atoms, they will no longer need to protect a single kilogram measure in a Paris vault.

The sphere was created at a cost of 2 million euros ($3.17 million) and took some five years to make, AFP reported.

However, Becker said it only weighs "approximately" a kilogram. He added that it does not need to weigh precisely a kilogram because the researchers will calculate the exact number of silicon atoms in a kilogram once they determine how many atoms are in the sphere.

Any changes to the kilogram measure as we know it would be so minor, that it would only interest scientists, he said.