US scientists plan to harness the by-products of cosmic rays to detect hidden nuclear material, probe Mexican pyramids and predict eruptions in volcanoes in Japan.

Several research groups speaking at the annual meeting of the AAAS (American Association for the Advancement of Science), suggest using muons, charged particles formed when cosmic rays hit the atmosphere, to scan dense objects. A team in Mexico is already using so-called muon radiography to look for burial chambers in the Pyramid of the Sun in Teotihuacan, and Japanese researchers are using a similar technique to look into the interior of volcanoes, to assess how likely they are to erupt. Meanwhile, scientists at the Los Alamos lab in New Mexico are exploring muon tracking as a way of seeing into closed containers going through customs.

Muons strike the Earth at a rate of about 10,000 per square metre every minute, and their courses are deflected by the material they pass through. Researchers can tell what kind of material they have passed through by how much their course changes, and because they are charged, these deflections are easy to track. All groups are tracking the paths of naturally occurring muons to obtain their data, a fact the US team sees as a big advantage over other scanning technologies, such as potentially harmful X-Rays or neutrons.

According to the Los Alamos researchers, truck drivers could remain in their vehicles while they are scanned. Christopher Morris, a member of the Los Alamos team explained that each scan lasts between 30 and 60 seconds, and the detectors can spot a four by four by four inch cube of uranium in a metal container full of sheep.

"We've been fighting the general perception that there are not enough muons to measure," Morris said. "There really are." The team is developing better software techniques to allow rapid 3-dimensional images of the volumes being screened, he added.

The detectors are still in a developmental phase, and are likely to cost around a million dollars a piece when they are ready for market. However, Morris says he is confident of the contribution the technology will make to the security of the US' borders. ®

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