Scientists find tiny new ways to measure up

We've come a long way from the days when the length of the king's forearm was used to determine an object's size.

Then, it was called the cubit, but the succession of short- and long-limbed kings made uniformity difficult. More modern standardized measures have helped. But these days, even those aren't enough.

That's why the agency that sets measurement standards for the United States - the National Institute of Standards and Technology - is asking American technologists to assess the needs for new ones. With 80 percent of world trade dependent on such standards, NIST wants to be up to speed.

What may sound like tedious nitty gritty is an awesome challenge, especially in today's nanotechnology era, where some machines are the size of pollen grains.

A couple of recent announcements make the point. Paul Alivisatos and colleagues at the University of California in Berkeley are developing a way to measure the distance between molecules across arrays of proteins. They bind tiny gold particles to molecules. Then, by watching how these particles scatter light, the researchers estimate their separation distance. The changing color of scattered light reveals changing separation. This, in effect, is a "ruler" for measuring distances on a molecular scale.

Meanwhile, another research team has come up with a different kind of atomic-scale ruler.

Team members at JILA, an institute established jointly by NIST and the University of Colorado on the university's Boulder campus, use laser-generated ultraviolet (UV) light to create a ruler.

The laser pulses are so precisely timed and so finely spaced that they look like evenly spaced teeth in a hair comb when represented by a graph. NIST compares the fast, accurate laser pulsing to a camera with superfast shutter speeds and consistent shot-to-shot performance. The device should enable scientists to take what NIST calls "real-time pictures" of atomic- and molecular-scale events.

To get a feel for these events, consider this: An atom can be in different energy states. When it changes from one energy level to another, it emits or absorbs light of a precise frequency. That process happens very fast.

Scientists have been measuring these transitions and identifying atoms by them for over a century. Yet they have not been able to do this with extremely high precision.

The new "UV ruler," based on laser pulses that last just a few millionths of a billionth of a second, makes it possible to see what NIST calls "more precise differences than ever before" between an atom's energy levels.

The need for 21st-century weights and measurement standards is not felt by the nanotech crowd alone. It's a necessity for all sizes and shapes of things that enter into scientific research and into commerce.

NIST acting director Hratch Semerjian calls these standards "a vital element of our innovation infrastructure." He adds that the US measurement system should sustain the economy "at world-class levels in the 21st century."

Why, then, does the US stick so tenaciously to what a Dutch observer called "your crazy foots and pounds?"

The rest of the world - including neighboring Canada and Mexico - works on the metric system.

Indeed, why doesn't the US fully adopt that system when it already is a legally authorized alternative?

Staying above the fray, the politically astute NIST does not raise this sensitive issue in announcing its project to "road map" the nation's future measurement needs.

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