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Nuclear Decay May Vary With Earth-Sun Distance
KentuckyFC writes "We've long thought that nuclear decay rates are constant regardless of ambient conditions (except in a few special cases where beta decay can be influenced by powerful electric fields). So that makes it hard to explain two puzzling experiments from the 1980s that found periodic variations over many years in the decay rates of silicon-32 and radium-226. Now a new analysis of the raw data says that changes in the decay rate are synchronized with each other and with Earth's distance from the sun. The physicists behind this work offer two theories to explain why this might be happening (abstract). First, some theorists think the sun produces a field that changes the value of the fine structure constant on Earth as its distance from the sun varies. That would certainly affect the rate of nuclear decay. Another idea is that the effect is caused by some kind of interaction with the neutrino flux from the sun's interior which also varies with distance. Take your pick. What makes the whole story even more intriguing is that for years physicists have disagreed over the decay rates of several isotopes such as titanium-44, silicon-32, and cesium-137. Perhaps they took their data at different times of the year?"
The Voyagers was the first thing that came to my mind, too. If the rate of radioactive decay is dependent on neutrino flux from the sun, then shouldn't their RTGs have long since gone dead as the rate of decay slowed (due to increasing distance), rather than maintaining better performance than originally anticipated (due to better performance of the thermocouple than anticipated)? (NASA link) Given that both spacecraft are alive and well out past the heliosphere, I think we can safely conclude that the rate of decay of the plutonium onboard is not meaningfully influenced by solar neutrino flux.