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The Sun is changing the rate of radioactive decay, and breaking the rules of chemistry

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The Sun is changing the supposedly constant rates of decay of radioactive elements, and we have absolutely no idea why. But an entirely unknown particle could be behind it. Plus, this discovery could help us predict deadly solar flares.

It's one of the most basic concepts in all of chemistry: Radioactive elements decay at a constant rate. If that weren't the case, carbon-14 dating wouldn't tell us anything reliable about the age of archaeological materials, and every chemotherapy treatment would be a gamble. It's such a fundamental assumption that scientists don't even bother testing it anymore. That's why researchers had to stumble upon this discovery in the most unlikely of ways.


A team at Purdue University needed to generate a string of random numbers, a surprisingly tricky task that is complicated by the fact that whatever method you use to generate the numbers will have some influence on them. Physics professor Ephraim Fischbach decided to use the decay of radioactive isotopes as a source of randomness. Although the overall decay is a known constant, the individual atoms would decay in unpredictable ways, providing a random pattern.

That's when they discovered something strange. The data produced gave random numbers for the individual atoms, yes, but the overall decay wasn't constant, flying in the face of the accepted rules of chemistry. Intrigued, they checked out long range observations of silicon-32 and radium-226 decay, both of which showed a slight but definite variation over time. Intriguingly, the decay seemed to vary with the seasons, with the rate a little faster in the winter and a little slower in the summer.


At first, the researchers tried to rationalize the seasonal fluctuations as the result of instrument error, perhaps caused by changing heat and humidity. But that idea fell apart when nuclear engineer Jere Jenkins noticed the decay rate of the short-lived isotope manganese-54 dropped slightly during a solar flare. In fact, the decrease began a good 36 hours before the flare occurred.

That suggests two things: one that's theoretically puzzling, and another that's hugely exciting from a practical perspective. If decay rates really are affected by solar flares before the flares even occur, that could provide the first truly reliable early warning system for flares. Considering severe solar flares can wreak havoc on electrical grids and even kill astronauts who aren't properly protected, that would be a huge benefit for humanity.

But practical pluses aside, why is this happening? The seasonal fluctuations suggested the Sun could be involved somehow, and the solar flare connection confirmed it. The scientists speculated that solar neutrinos, the nearly massless particles created as byproducts of the sun's fusing of hydrogen atoms into helium, might be causing these variations. The fact that these neutrinos pass straight through the Earth with ease fit well with the fact that the decay rates were changing even at night, when the entire planet was between the radioactive isotopes and the Sun.

Once the researchers conclusively ruled out environmental influences, that left the Sun as the only possible cause of the decay variations. They also found that the amount of change varied in time with the Earth's orbit - the effect was greater when the orbit brought the Earth closer to the Sun and thus into contact with more neutrinos.


That's where renowned Stanford physics professor Peter Sturrock entered the picture. Confronted with this mystery, he advised the researchers to test how the decay fluctuations correlated with the Sun's own rotation. They found the decay rates recurred every 33 days, which didn't quite fit with the Sun's known surface rotation length of 28 days. But the neutrinos wouldn't be coming from the surface - they would be coming from deep inside the core. Unlikely as it might seem, the sun's core must be rotating a little slower than its surface, apparently once every 33 days.

All of this relies on some unlikely assumptions and the occasional bold intuitive leap, but the model they propose seems to hang together. And yet one mystery remains - how are the neutrinos managing to interact with the radioactive particles in this way? It doesn't fit with the known behavior of neutrinos, and it opens up the very real possibility that some previously unknown subatomic particle is actually behind this bizarre effect.


As Peter Sturrock explains:

"It's an effect that no one yet understands. Theorists are starting to say, 'What's going on?' But that's what the evidence points to. It's a challenge for the physicists and a challenge for the solar people too. [If it's not neutrinos,] it would have to be something we don't know about, an unknown particle that is also emitted by the sun and has this effect, and that would be even more remarkable."


If these new discoveries hold up, then we've discovered that the sun changes rates radioactive decay, that we can predict solar flares before they happen, that the sun's core rotates slower than its surface, and maybe even that an entirely unknown particle exists and is affecting our world in a tangible way. Not a bad set of results for what was supposed to be a simple search for some random numbers.

[Symmetry Breaking]