Planes in thunderstorms cop gamma ray bursts

It's long been known that flying exposes people to more cosmic rays than land-lubbers, but new research suggests another source of airborne irradiation: high-energy “dark lightning” that gives rise to gamma radiation.

Florida Institute of Technology researcher Joseph Dwyer outlined the idea at a meeting of the European Geosciences Union in Vienna recently, with the comforting news that such bursts don't produce enough radiation to be dangerous.

Whereas normal lightning is caused by a relatively slow movement of electrons, leading to a charge build-up that's sufficient to break down the insulating properties of air, the “dark lightning” is released by much higher-energy electrons, Dwyer told LiveScience.

The high-energy electrons give rise to gamma radiation when they collide with air particles, Dwyer says, in turn creating new electron/positron pairs that keep the cycle going with further collisions. However, the large amounts of energy released each time mean the cycle is short, and the electric fields “can collapse in a few tens of microseconds”.

Dwyer's model suggests that at 40,000 feet (about 12,000 metres) – near the tops of thunderstorms – radiation doses would be equivalent to a person's normal annual background radiation. In the middle of a storm, at about 16,000 feet (about 5,000 metres) the dose would be much higher.

However, these are conditions that airline pilots routinely avoid unless it's impossible to do so, and a passenger would only get a high dose if they were in exactly the wrong place at the wrong time. He told LiveScience that doses “never seem to reach truly dangerous levels”.

Discovery notes that the National Science Foundation is working on an armoured plane to fly through thunderstorms, which could carry instruments to get an accurate fix on gamma radiation released by dark lightning. ®