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Science

Nuclear Decay May Vary With Earth-Sun Distance 418

Posted by kdawson
from the not-so-fast-there dept.
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?"
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Nuclear Decay May Vary With Earth-Sun Distance

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  • by Anonymous Coward on Friday August 29, 2008 @09:11AM (#24793223)
    the sun produces a field that changes the value of the fine structure constant on Earth

    variable constant

  • by Wills (242929) on Friday August 29, 2008 @09:21AM (#24793365)

    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).

    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 [wikipedia.org] and the quantum anti-Zeno effect. [wikipedia.org]

  • Re:Carbon Dating (Score:3, Insightful)

    by Lodragandraoidh (639696) on Friday August 29, 2008 @09:25AM (#24793411) Journal

    I am more concerned about the other end of that - time-keeping --- the communications networks get their time hacks from clocks based upon the decay rate of isotopes (e.g. a cesium clock).

    The cool thing is, if this periodical effect is a constant function, then we can adjust our clocks based upon this new knowledge -- making them more accurate over the long haul.

    As for carbon dating, assuming what I said was true, I don't see why you could not apply the function to get a more accurate reading - not that carbon dating is that accurate to begin with (from a human standpoint - if you are talking about increasing your accuracy by hours or even days -- that still lays well within the realm of statistical noise when you are talking about millions of years).

  • Re:Pioneer Anomaly (Score:1, Insightful)

    by Anonymous Coward on Friday August 29, 2008 @09:35AM (#24793559)

    Well if you can get all the ejected mass to go in the same direction you just might get an effect that just migh tbe measurable with really good instruments.

    But as the ejected particles will go in random directions, the net effect will be zero.

  • Cesium decay (Score:4, Insightful)

    by mcvos (645701) on Friday August 29, 2008 @09:38AM (#24793595)

    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?

  • my pick (Score:3, Insightful)

    by mapkinase (958129) on Friday August 29, 2008 @09:39AM (#24793615) Homepage Journal

    I use my own Occam's blade to cut off the first one and pick the second one.

  • by Geoffrey.landis (926948) on Friday August 29, 2008 @09:45AM (#24793691) Homepage
    But... look at the data [arxivblog.com]. That correlation is *terrible*. The phase is off.

    Also, note that since the perihelion is right around Jan 1, only about eleven days after solstace-- this data equally well correlates with season.

  • Re:How To Test It (Score:4, Insightful)

    by jamie (78724) * Works for Slashdot <jamie@slashdot.org> on Friday August 29, 2008 @09:46AM (#24793715) Journal

    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.

  • by Colonel Korn (1258968) on Friday August 29, 2008 @09:59AM (#24793893)

    Could perhaps the distance between the earth and the sun and the relationship for nuclear decay be in some way effected by the gravitational field fluctuations that occur as well? Time is dilated by gravity, so perhaps are we seeing a further proof of Special relativity?

    Or are they simply looking for casual relationships where none actually exist. Perhaps the decay rate relates to the amount of pastafarians on earth.

    Since the measurement and the material are both in the same location, time dilation would affect them both to the same extent, meaning that the detector would not be able to measure a difference in the half life.

  • Re:Cool! (Score:3, Insightful)

    by Gewalt (1200451) on Friday August 29, 2008 @10:04AM (#24793973)
    It also means the next generation neutrino detectors are going to be nuclear decay based. That should prove interesting indeed.
  • by Gewalt (1200451) on Friday August 29, 2008 @10:06AM (#24794005)
    Unless the earth has changed orbit by a very significant factor, it doesn't make any difference at all.
  • Re:Carbon Dating (Score:3, Insightful)

    by mikael (484) on Friday August 29, 2008 @10:11AM (#24794093)

    It's actually based on the frequency of a transition in cesium, but the point is that these transitions are sensitive to the fine structure constant. If some field from the sun is changing that, it should be detectable in atomic clocks.

    Then an atomic clock in orbit around the Earth should speed up when it is nearest the Sun, and slow down when it is behind the Earth?

    Would Radioisotope thermoelectric generators [wikipedia.org] generate more energy when closer to the Sun, than away from the Sun, or simply shielded from it?

  • by Gerzel (240421) <brollyferret@NoSPaM.gmail.com> on Friday August 29, 2008 @10:14AM (#24794133) Journal

    Eh if so, then we'll just have to fix that with the next generation of probes. That's science for you.

    Learning comes more often from misses than hits as misses are far more common.

  • by blueg3 (192743) on Friday August 29, 2008 @10:31AM (#24794373)

    It seems more likely that an r^2 variation indicates that it's a field-like effect, which drops off as 1/r^2 (e.g., neutrino flux).

  • by Zenaku (821866) on Friday August 29, 2008 @10:31AM (#24794381)

    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.

  • by jschen (1249578) on Friday August 29, 2008 @10:34AM (#24794433)
    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 [nasa.gov]) 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.
  • by mooboy (191903) on Friday August 29, 2008 @10:38AM (#24794497)

    So our yellow sun... ...really can give Superman his powers!!!

  • Re:Carbon Dating (Score:4, Insightful)

    by kestasjk (933987) on Friday August 29, 2008 @11:12AM (#24795113) Homepage
    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.
  • by Yvanhoe (564877) on Friday August 29, 2008 @11:20AM (#24795243) Journal
    Could this explain Pioneer acceleration anomaly [wikipedia.org] ?
  • Re:Carbon Dating (Score:2, Insightful)

    by bigbigbison (104532) on Friday August 29, 2008 @11:29AM (#24795415) Homepage
    Exactly. That was my first thought too. Now the creationist design people will use this as more "proof" that science is wrong without really understanding what it means.
  • by goodmanj (234846) on Friday August 29, 2008 @12:07PM (#24796097)

    The authors just chose to plot vs r^2, rather than r. Since the data is noisy and Earth's orbit is only slightly elliptical, the data would correlate just as well to r.

  • by avandesande (143899) on Friday August 29, 2008 @12:12PM (#24796171) Journal

    We don't know that the neutrino flux is constant. Neutrinos are notoriously hard to detect and measure.

  • by Kupfernigk (1190345) on Friday August 29, 2008 @12:33PM (#24796561)
    This could be one of those "oh shit" moments. Nowadays, when the slightest observational anomaly gets string theorists salivating, perhaps we need to lay in a stock of Bill Ockham's finest razor blades.
  • Re:Seriously : No (Score:3, Insightful)

    by Vellmont (569020) on Friday August 29, 2008 @02:31PM (#24798449)


    Suppose the sun drifted into some cloud of dark matter a billion years ago and that messed things up?

    You can suppose a lot of things if you're ignorant enough and try hard. We don't even know if this phenomenon is real, much less if it's caused by neutrinos. Where you got "dark matter" involved I don't really understand. (We also don't really know what dark matter even is).

    A few hundred years ago you could have convinced a scientist that you could manipulate gravity (with hidden electromagnets).

    Maybe a really dumb scientist. Charlans existed a few hundred years ago, and so did magnets.

    There could be all kinds of fields at work in the universise that haven't been apparent to us simply because they're flat on the scale that we've experienced them.

    That's certainly possible. Supposing they exist before you have any real evidence for them isn't science though. Going down the road of unobserved forces leads to stuff like epicycles [wikipedia.org] (which does work if you believe in unobserved forces). You're right that we likely don't understand everything in physics. You're wrong that we should start speculating in ignorance about what those things might be. Science works best at filling in the gaps of knowledge, not supposing gaps that we don't even know are there.

I cannot conceive that anybody will require multiplications at the rate of 40,000 or even 4,000 per hour ... -- F. H. Wales (1936)

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