Researchers believe they've found a way of predicting solar flares more than a day before they occur, possibly helping to protect satellites, power grids and astronauts from dangerous radiation.
The system works by measuring differences in gamma radiation emitted when atoms in radioactive elements decay. This rate of decay has long been believed to be constant - but may not be, says the Purdue University team.
The new technique is based on the hypothesis that radioactive decay rates are influenced by solar activity, such as the streams of subatomic particles called solar neutrinos. This influence, say the scientists, can vary with seasonal changes in Earth's distance from the sun and also during solar flares.
"It's the first time the same isotope has been used in two different experiments at two different labs, and it showed basically the same effect," says physics professor Ephraim Fischbach.
Data was recorded over six years during the routine weekly calibration of an instrument used for radiological safety at Ohio State's research reactor - and showed a clear annual variation in the decay rate of the radioactive isotope chlorine 36. The highest rate was observed in January and February, and the lowest in July and August.
The findings agree with data previously collected at the Brookhaven National Laboratory regarding the decay rate of chlorine 36.
"When the Earth is farther away, we have fewer solar neutrinos and the decay rate is a little slower," says nuclear engineer Jere Jenkins. "When we are closer, there are more neutrinos, and the decay a little faster."
As the sun approaches its 11-year solar maximum, protection from flared is becoming more important. A good warning system could see satellites and power grids protected or temporarily shut down in advance of a solar storm.