Washington, Sept. 22 : The news that the official kilogram – a cylinder cast made 118 years ago from platinum and iridium -- has been losing mass, about 50 micrograms at the last check at a storage facility near Paris, has prompted two U.S. professors – a physicist and mathematician to look for other ways to define the kilogram better.

The official kilogram is known as the "International Prototype Kilogram or “Le Gran K”.

Ronald F. Fox, a Regents’ Professor Emeritus in the School of Physics at the Georgia Institute of Technology and Theodore P. Hill, a Professor Emeritus in the Georgia Tech School of Mathematics, have launched a campaign aimed at redefining the kilogram as the mass of a very large – but precisely-specified – number of carbon-12 atoms.

“Our standard would eliminate the need for a physical artifact to define what a kilogram is. We want something that is logically very simple to understand,,” said Fox.

Their proposal is that the gram – 1/1000th of a kilogram – would henceforth be defined as the mass of exactly 18 x 14074481 (cubed) carbon-12 atoms.

The proposal made by Fox and Hill first assigns a specific value to Avogadro’s constant.

Proposed in the 1800s by Italian scientist Amedeo Avogadro, the constant represents the number of atoms or molecules in one mole of a pure material – for instance, the number of carbon-12 atoms in 12 grams of the element. However, Avogadro’s constant isn’t a specific number; it’s a range of values that can be determined experimentally, but not with enough precision to be a single number.

In the fall of 2006, Fox and Hill submitted a paper to Physics Archives in which they proposed assigning a specific number to the constant – one of about 10 possible values within the experimental range. The authors pointed out that a precise Avogadro’s constant could also precisely redefine the measure of mass, the kilogram.

Their proposal drew attention from the editors of American Scientist, who asked for a longer article published in March 2007.

The proposal has so far drawn five letters, including one from Paul J. Karol, chair of the Committee on Nomenclature, Terminology and Symbols of the American Chemical Society.

In September 2007, when Fox read an Associated Press article on the CNN.com Web site about the mass disappearing from the International Prototype Kilogram, he argued that the amount could be significant in a world that is measuring time in ultra-sub-nanoseconds and length in ultra-sub-nanometers.

So, he and Hill fired off another article to Physics Archive, this one proposing to redefine the gram as 1/12th the mass of a mole of carbon 12 – a mole long being defined as Avogrado’s number of atoms.

They now hope to generate more interest in their idea for what may turn out to be a competition of standards proposals leading up to a 2011 meeting of the International Committee for Weights and Measures.

At least two other proposals for redefining the kilogram are under discussion. They include replacing the platinum-iridium cylinder with a sphere of pure silicon atoms, and using a device known as the “watt balance” to define the kilogram using electromagnetic energy. Both would offer an improvement over the existing standard – but not be as simple as what Fox and Hill have proposed, nor be exact, they say.

The kilogram is the last major standard defined by a physical artifact rather than a fundamental physical property. In 1983, for instance, the distance represented by a meter was redefined by how far light travels in 1/299,792,458 seconds – replacing a metal stick with two marks on it.

While the new definition would do away with the need for a physical representation of mass, Fox says people who want a physical artifact could still have one – though carbon can’t actually form a perfect cube with the right number of atoms. And building one might take some time. (With inputs from ANI)