Slashdot Mirror
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?"
If you count the presence or absence of observation as part of "ambient conditions", there are two cases where nuclear decay rates are affected by ambient conditions: The quantum Zeno effect and the quantum anti-Zeno effect.
Scroogle
I'm more worried about the effect on Cesium decay. Did we accidentally base our definition of time on a variable rather than a constant?
Also, note that since the perihelion is right around Jan 1, only about eleven days after solstace-- this data equally well correlates with season.
http://www.geoffreylandis.com
Yeah, kdawson and I have been discussing this. This is an interesting story but of course the research needs to be duplicated and checked, objections need to be raised and addressed and so on.
Cassini is a good example... for the past 11 years it's carried 30 kg of Pu-238 from Earth (1 AU) to Saturn (10 AU), and its decay has been its only source of electrical power. If the Earth's 3% annual variation in distance from the Sun causes a 0.4% variation in the half-life of radioactive silicon, wouldn't the 900% change in Cassini's solar distance caused, at the very least, a head-scratcher for mission control?
So I'm super-skeptical about this.
The hard part about running tests to confirm this alleged effect here on Earth is that it may take years to get convincing results. One might also put a few samples of radioactive materials and sensitive detectors on HEO satellites and get a 0.1% change in solar distance every few days. If there's a detectable difference in radioactive decay it could be statistically significant in a matter of weeks. Rather expensive test, though. My guess is there's a better explanation for the observed effect (seasonal changes in temperature/humidity on the detection equipment maybe) and after a handful of grad students write papers about their inability to replicate the effect, this will be dismissed and filed away. Still interesting though.
If I understood correctly, the variance in decay rate between Earth's aphelion and perihelion is .1%. Earth's distance from the sun doesn't change by that much in astronomical terms. If we see a .1% variation over that relatively small distance, how different would the rate be at 100AU, or half-way to the nearest star? How do we know that radioactive isotopes decay at all if you get them far enough away from a star?
It's also not simply a matter of how long the power supply will last. Those generators work by converting the heat from each decay event into electricity, and if the rate of decay is less than it should be, then it will not produce continuous power.
I'm not saying that it's definitely a problem, I just think this raises interesting questions.
If fate makes you a motorcycle, you become a motorcycle.
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.
It's still a depressing thought though. You can just imagine the Bible literalists latching onto this as a way to dismiss evidence based on radioactive decay.
// MD_Update(&m,buf,j);
Could this explain Pioneer acceleration anomaly ?
The Wise adapts himself to the world. The Fool adapts the world to himself. Therefore, all progress depends on the Fool.