Science 1663

Spotlight

Terrorists Beware, Big City's Life on the Line, Protons, Camera—Action, A Big SCORE, High-Altitude Dowsing

Terrorists Beware!

Now and then, there really is such a thing as a free lunch. This one—served up by Mother Nature—could foil terrorist attempts to smuggle an atomic bomb, or its parts, into the country.

In collaboration with Decision Sciences Corporation, Los Alamos researchers have found a way to use cosmic-ray muons— subatomic particles that constantly stream down from the heavens—to detect plutonium or uranium hidden in a vehicle or shipping container. Unlike current x-ray inspection methods, which expose a vehicle’s occupants or a container’s contents to a manufactured dose of x-rays, muon inspection involves only the natural muon exposure from cosmic rays that are already part of background radiation.

About 10,000 cosmic-ray muons rain down on every square yard of Earth’s surface each minute. Most of them have enough energy to penetrate several feet of lead, which means they are only slightly deflected from their downward path as they pass through the thin steel roof of a car or truck. However, chunks of plutonium or uranium deflect the muons more noticeably: their highly charged atomic nuclei produce large electrostatic forces that bend the path of the electrically charged muons.

A vehicle-scanning system, including panels of charged-particle detectors above, below, and at the sides of a vehicle, determines the path of each muon before and after it passes through the vehicle. Computers analyze the paths, looking for bomb materials and their tell-tale deflections and flagging many suspicious objects in about a minute or more. The panels can be built into a structure and/or otherwise camouflaged so that smugglers will not even know they’re being scanned.

Big City’s Life on the Line

A “New York minute,” slang for “a very short time,” refers to the common feeling that life is faster in big cities. This perception was recently borne out in studies that show how urban indicators, which include “social currencies” such as wealth creation, innovation, and information, but also crime rates and how fast people walk, vary with urban population size.

Using data from hundreds of cities worldwide, a team of researchers, including two Los Alamos theorists, found that social currencies increase per capita with population, while material infrastructure (the size of the energy grid, transportation network, etc.) grows more slowly than population. These findings apply to all urban systems studied, from the U.S. to China.

The researchers also introduced a new “urban growth equation” that relates urban population to the availability of resources and their consumption. The equation shows that, as populations grow, social life accelerates because many more contacts become possible between people.

Furthermore, the researchers found that when urban development is driven by social interactions, the relative growth rate steadily increases, which leads inexorably to crises. Sustainable growth can nevertheless be achieved through periodic resetting of the growth trajectory via major adaptations, leading to successive growth cycles. Historically in the U.S., such adaptations have resulted from shifts in immigration, the Civil War, the Great Depression, and the result of urban interventions.

The study’s conclusions—that cities are predictable accelerators of social life and that the rate of urban population growth periodically undergoes abrupt changes, which must occur more often as the city’s population increases—are confirmed by the analysis of New York City’s historic growth. Such insights could help guide new policies on sustainable development in a world that is becoming predominantly urbanized. The work is published in the Proceedings of the National Academy of Sciences, Vol. 104, pp. 7301–7306, 2007.

Protons, Camera—Action!

Lab researchers, working with Teledyne Imaging Sensors, have built the world’s fastest camera, and it has just won an R&D 100 Award from R&D Magazine as one of the 100 most technologically significant products of 2007.

Made from two bonded microelectronic chips, the “Camera on a Chip” can capture 2.8 million frames per second. A normal motion picture camera captures 24 frames per second.

The camera produces movies of ultra-short (sub-microsecond) processes, mostly induced by powerful high explosives. These processes are studied using a remarkable imaging technique known as proton radiography, in which high-energy protons pass through an explosives-driven object to a screen, where they produce a blue “shadowgraph,” essentially a two-dimensional representation of the object.

The camera takes pictures of the shadowgraphs in as little as 50 billionths of a second per frame, freezing images of the object’s high-speed motions and storing up to three of them “on-chip” at one time. Several cameras can be used together to make a movie of tens of frames or more.

With very high sensitivity in both the visible and near-visible frequencies, the camera can also be used for many other applications, including studies of internal-combustion engines, vehicle-impact tests, and armor-penetration experiments; laser-beam identification of minerals on Mars; and location of fast-moving targets in space.

A Big SCORE

Across the globe, two billion people use open fires as their primary cooking method—with 93 percent of the energy produced going up in smoke. A simple appliance being developed by a consortium that includes Los Alamos scientists could change all that.

Photo credit: Paul Reilly, www.score.uk.com/research/

The Stove for COoking, Refrigeration, and Electricity supply (SCORE) would employ thermoacoustic technology to capture some of the energy left in the flue gases after cooking to provide refrigeration and electricity. The flue gases from the burning biomass will unevenly heat air contained in specially shaped pipes; some in the stove’s chimney and others behind the stove. Temperature differences produced by the uneven heating will cause the air in the pipes to oscillate, generating intense sound waves. These will produce electricity by moving a diaphragm attached to a coil of wire near a permanent magnet—like a loudspeaker in reverse.

Other sections of the piping form an acoustically powered refrigerator. The sound waves entering those pipes provide cooling by compressing and expanding the air while moving it between cold and ambient heat exchangers.

Led by the University of Nottingham in the United Kingdom, the consortium also includes other universities, industry, and a charity. Scott Backhaus, at Los Alamos, says the consortium would like to produce about a million SCOREs within five years for about $40 per unit and train villagers to build most of the stove’s parts themselves—largely from local sources of scrap metal—and then maintain the appliance.

Backhaus notes that SCORE will improve cooking efficiency and provide refrigeration for rural inhabitants of Africa, Asia, and other parts of the world. But by providing enough electricity to charge cell-phone batteries and run computers, SCORE may actually help the Third World catch up to the First.

High-Altitude Dowsing

Since forever, dowsers have searched for groundwater by walking through fields and observing the twitchings of a Y- or L-shaped divining rod. Los Alamos scientists have advanced that ancient art by replacing the rod with large, electrically energized coils of wire, carried not by hand, but aboard a four-engine aircraft.

In 2001, the scientists flew the coils over parts of the Pajarito Plateau in northern New Mexico, the Laboratory’s home base, and conducted an electromagnetic survey to characterize local aquifers and contamination pathways. They collected data on the electrical resistivity of Earth’s surface layer, a measurement that is highly sensitive to groundwater. When that data was combined with existing geochemical and geophysical borehole data, the results revealed “wet” and “dry” areas of the plateau to depths of 1,000 feet or more. The survey, an important case study of the method, is published in Geophysics, Vol. 72, pp. B31–B45, 2007.