MIAMI, Florida -- Lightning partly consists of X-rays which fire out just before the visible flash, scientists confirm. The discovery settles a long standing debate dating back to 1925 when it was first suggested that thunderstorms may produce high-energy radiation.

Testing the theory has been difficult because of the sporadic nature of lightning and the "electromagnetic noise" it generates. Scientists in Florida, in the United States, studied artificial lightning using a hi-tech version of ben Franklin's famous kite experiment.

In 1752 Franklin demonstrated that lightning was electric in nature by flying a child's kite in a thunderstorm. Lightning struck the kite and passed down the string to a metal key connected by metal wire to a leyden jar, a device for storing static electricity.

The scientists at the University of Florida's Lightning Research Center did something similar by firing rockets trailing a grounded copper-kevlar wire into a thundercloud. At 2000 feet, the rocket triggered a lightning bolt which vaporized the wire, and unleashed a number of natural strikes. The researchers measured intense bursts of electronic radiation -- X-rays, Gamma rays and fast-moving electrons -- just before each flash, during the non-visual phase of the lightning strike.

Each burst typically lasted less than 100 microseconds and deposited many tens of megaelectron volts into a detector. "These results provide strong evidence that the production of runaway electrons is an important process during lightning," the researchers wrote in the journal*** Science.**** The findings complement recent observations of X-ray bursts associated with natural lightning. "X-rays and other kinds of electronic radiation may be generated during the leader" phase, the phase that creates a path from clouds to the ground for lightning to follow, said the scientists.(DPA)