Cosmic rays to throw light on pyramid

The secrets of a 2,000-year-old pyramid are set to be revealed, illuminated by the "light" cast by incoming cosmic rays. A researcher hopes particles created by the rays will identify burial chambers or hidden passageways in the Pyramid of the Sun in Mexico.

Treasure hunting in a giant pyramid was just one possible use for muons, charged particles created when cosmic rays strike our atmosphere. The AAAS meeting in Washington heard that muon detectors might also be useful for "seeing" magma rising in volcanoes or spotting radioactive materials being smuggled in trucks or shipping containers.

The earth is constantly bombarded by cosmic radiation coming from deep space, and these rays kick off huge numbers of muons. They strike the earth at rates up to 10,000 per square metre per minute, the meeting heard.

Their value is based on the muon's ability to pass effortlessly through rock or metal. Their small change makes them easy to track as they pass through large objects, whether pyramids or articulated lorries.

The pyramid, at Teotihuacan, 30 miles north of Mexico City, is a complete mystery, according to Dr Arturo Menchaca-Rocha, director of the physics institute at the National Autonomous University of Mexico.

The civilisation that built it is unknown and it was abandoned 600 years before the Aztecs arrived in the region, he said. It is colossal, measuring 740 feet across and standing 215 feet high.

He hopes to use the penetrating muons to illuminate any burial vaults or similar features inside the pyramid. He will use a muon detector about a metre square placed in an ancient tunnel that runs under the base of the pyramid.

Surplus muons striking the detector could indicate voids, open spaces or rooms that could be targeted by archaeologists. The detector will allow almost the entire pyramid to be scanned in one go.

Dr Kanetada Nagamine of the KEK Muon Science Laboratory in Japan is using muons to measure the rise and fall of volcano lava. He hopes the data may make volcanic eruptions easier to predict.