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Why the kilogram is getting heavier (and why a “sun tan” is the remedy)

By James Holloway

January 7, 2013

According to researchers at Newcastle University in the United Kingdom, the kilogram is very likely getting heavier. How can this be? Mainly because we’re talking about the definitive kilogram, the International Prototype Kilogram (IPK) kept at the International Bureau of Weights and Measures in Paris. But because this is the kilo against which all kilos are defined, in a theoretical sense at least, all kilograms will technically be heavier too.

The IPK is a small cylinder of platinum-iridium alloy, about 39 mm (or an inch and a half) in both height and diameter. Using a unique Theta-probe XPS machine, Professor Peter Cumpson and Doctor Naoko Sano of Newcastle University have analyzed surfaces similar to those of the IPK to quantify the build-up of hydrocarbon contaminants. Their research indicates that the IPK is likely to have gained tens of micrograms in mass since the standard was introduced in 1875.

XPS stands for X-ray Photoelectron Spectroscopy, a process which involves irradiating a material with X-rays, and analyzing the quantity and energy of the electrons that are emitted, granting insights into the surface chemistry of the material, and the differences in it before and after some process (such as cleaning). What makes the researcher’s XPS machine unique is its argon cluster ion gun which emits charged clusters of argon, each containing around a thousand atoms. It’s this component that allows analysis of the organic layer – the gunk – without damaging the underlying inorganic material.

read more http://www.gizmag.com/why-the-kilogram-is-getting-heavier-an...